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  • General Chemistry  (77.717)
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  • 1
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    Quantification of bone surface textures: exploring a new method of ontogenetic ageing (2023)
    In:  Journal of Analytical Science and Technology vol. 14 no. 1
    Details
    Publikationsdatum: 2024-02-26
    Beschreibung: Identifcation of ontogenetic age classes plays an important role in the felds of zoology, palaeontology and archaeology, where accurate age classifcations of (sub)fossil remains are a crucial component for the reconstruction \nof past life. Textural ageing\xe2\x80\x94the identifcation of age-related bone surface textures\xe2\x80\x94provides a size-independent \nmethod for age assessment of vertebrate material. However, most of the work so far is limited to qualitative results. \nWhile qualitative approaches provide helpful insights on textural ageing patterns, they are heavily subject to observer \nbias and fall short of quantitative data relevant for detailed statistical analyses and cross-comparisons. Here, we present a pilot study on the application of 3D surface digital microscopy to quantify bone surface textures on the long \nbones of the grey heron (Ardea cinerea) and the Canada goose (Branta canadensis) using internationally verifed \nroughness parameters. Using a standardised measuring protocol, computed roughness values show a strong correlation with qualitative descriptions of textural patterns. Overall, higher roughness values correspond to increased numbers of grooves and pits and vice versa. Most of the roughness parameters allowed distinguishing between diferent \nontogenetic classes and closely followed the typical sigmoidal animal growth curve. Our results show that bone \ntexture quantifcation is a feasible approach to identifying ontogenetic age classes.
    Schlagwort(e): General Physics and Astronomy ; General Environmental Science ; General Biochemistry ; Genetics and Molecular Biology ; General Materials Science ; General Chemistry ; Roughness ; Surfaces ; Taphonomy ; Topography ; Bone ; Ontogeny ; Digital microscopy
    Repository-Name: National Museum of Natural History, Netherlands
    Materialart: info:eu-repo/semantics/article
    Format: application/pdf
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  • 2
    Digitale Medien
    Digitale Medien
    Self-Assembly of Bisurea Compounds in Organic Solvents and on Solid Substrates (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1238-1243 
    Details
    ISSN: 0947-6539
    Schlagwort(e): gels ; electron microscopy ; scanning tunneling microscopy ; self-assembly ; ureas ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: New low molecular weight gelators based on the structure R—NHCONH—X—NHCONH—R have been synthesized and tested for their ability to cause gelation of organic solvents. Compounds 2 (R = n-dodecyl, X = -(CH2)9-), 3 (R = n-dodecyl, X = -(CH2)12-), 4 (R = n-dodecyl, X = 4, 4′-biphenyl), and 5 (R = benzyl, X = -(CH2)9-) form thermoreversible gels with a wide range of organic solvents, at concentrations well below 10 mgmL-1. Depending on the nature of the R and X groups, the solvents that undergo gelation include hexadecane, p-xylene, 1-octanol, n-butyl actetate, cyclohexanone, and tetralin. The gels are stable up to temperatures well above 100°C, but are easily disrupted by mechanical agitation. Light microscopic investigations revealed that compounds 2-5 spontaneously aggregate to form thin flat fibers, which can be several hundreds of micrometers long and only 2-10 μm wide. Depending on the solvent, multiple twists in the fibers are observed. In the gels, these fibers form an extended three-dimensional network, which is stabilized by multiple mechanical contacts between the fibers. Electron microscopy and X-ray powder diffraction revealed that the fibers consist of stacks of sheets. The thickness of the sheets is 3.65 and 3.85 nm for 2 and 3, respectively. Scanning tunneling microscopic investigations of 2 absorbed on graphite showed that 2 forms long ribbons with a width of 5.0 nm. In the ribbons the molecules have a parallel arrangement, with the long molecular axis perpendicular to the long ribbon axis. The two urea groups within a given molecule are each part of mutually parallel extended chains of hydrogen bonds. Based on these observations a model is proposed for the arrangement of the molecules in the fibers. In this model the bisurea molecules aggregate through hydrogen-bond formation into long ribbons, which assemble into sheets. In these sheets the ribbons are tilted. Finally, the sheets stack to form long thin fibers. This model is supported by molecular dynamics simulations.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970030811
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  • 3
    Digitale Medien
    Digitale Medien
    Tripodal Synthetic Peptide BundlesDedicated to Professor Wolfgang Beck on the occasion of his 65th birthday (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1254-1268 
    Details
    ISSN: 0947-6539
    Schlagwort(e): peptide bundles ; peptides ; pseudo-peptides ; template synthesis ; tripodal ligands ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The stereochemical course of the formation of the two diastereomers of trimethyl 2,2′,2″-nitrilotris[2-(benzoylamino)acetate], 2a and 2b, is described. The structures of both isomers were confirmed by X-ray diffraction studies. Diastereomer 2b could be obtained in larger quantities by epimerisation of 2 a to 2 b with catalytical amounts of NaOMe. The (RRR/SSS)-triester 2 b is a suitable template for the synthesis of tripodal peptide bundles. Saponification of 2 b yielded the C3-symmetrical racemic triacid 4 b, which was coupled with amino acid methyl esters and dipeptide esters to give pseudo-hexapeptides and pseudo-nonapeptides, respectively. The resulting mixtures of diastereomers were easily separated by crystallisation. Their absolute configuration at the template unit (RRR or SSS) was established by means of the CD spectra. The pseudo-hexapeptide (SSS)N(BzGly*ValOMe)3 (14) was saponified to yield the optically pure triacid (SSS)N(BzGly*ValOH)3 (23). Compound 23 is an ideally preorganised template for the production of longer tripodal peptides. This was illustrated by the synthesis of two pseudo-pentadecapeptides. Peptide bundles with polar side chains (histidine and serine) or end groups (catechol or hydroxamate units) were synthesised by using the templates 4 b, 22 and 23 as anchors.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970030813
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  • 4
    Digitale Medien
    Digitale Medien
    Noncovalent Assembly of Functional Groups on Calix[4]Arene Molecular Boxes (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1823-1832 
    Details
    ISSN: 0947-6539
    Schlagwort(e): calixarenes ; hydrogen bonds ; molecular boxes ; noncovalent assembly ; supramolecular chemistry ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Calix[4]arenes diametrically substituted at the upper rim with two melamine units spontaneously form well-defined box-like assemblies in the presence of two equivalents of 5,5-diethylbarbituric acid. These assemblies, consisting of nine different components, are held together by 36 hydrogen bonds and are stable in apolar solvents at concentrations of up to 10-4M. This paper reports the first X-ray crystal structure, and the MALDI TOF mass spectra together with the complete 1H NMR spectroscopic characterization of these hydrogen-bonded assemblies. The crystal structure clearly shows that the assemblies are stereogenic, as a result of the antiparallel orientation of the two rosette motifs. Furthermore, the synthesis of twelve new 1,3-bis(melamine)calix[4]arenes carrying different numbers and types of functionalities at the upper rim is described. Detailed 1H NMR spectroscopic studies on the assembly behavior of these functionalized calix[4]arenes shows that 1) polar substituents (e.g. nitro, cyano) hardly affect the stability of the hydrogen-bonded assembly; 2) hydrogen bond donating or accepting groups, like amino and acetamido, can disturb assembly of the boxes under certain conditions by destabilizing the calix[4]arene pinched cone conformation as a result of intramolecular hydrogen bond formation; and 3) sterically bulky groups (e.g. tBu) can significantly inhibit the formation of the hydrogen-bonded assembly, but this effect very much depends on the exact positions of the groups.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031115
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  • 5
    Digitale Medien
    Digitale Medien
    Zinc(II)-Catalyzed Disproportionation in Rubber: The mechanism of Sulfur Vulcanization Revisited (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1846-1851 
    Details
    ISSN: 0947-6539
    Schlagwort(e): disproportionations ; dithiocarba-mate ; homogeneous catalysis ; vulcanization ; zinc ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Model studies have shown that cross-link precursors, that is, intermediates in the sulfur vulcanization of rubber, are transformed into cross-links by a nonsymmetric but regioselective disproportionation mechanism. Thus, two equivalents of the crosslink precursor of the type R—S—S—X are transformed into X—S—X and the actual cross-link R—S—S—S—R. Exchange of sulfur atoms is a prerequisite. A mechanism involving an SNi′ reaction with an allylic moiety, suggested in the literature, has not been observed. The disproportionation reaction is catalyzed by rubber-soluble zinc-dithiocarbamate complexes, an important class of vulcanization accelerators. By virtue of ligand-functional-group exchange reactions these complexes serve to transport and exchange sulfur atoms.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031117
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  • 6
    Digitale Medien
    Digitale Medien
    A Quintupled Superstructure of the KHg2 Type Realized for the New Stannide EuAuSn (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1852-1859 
    Details
    ISSN: 0947-6539
    Schlagwort(e): conductivity ; europium ; gold ; magnetic properties ; superstructures ; tin ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The title compound was prepared from the elements by reaction in a sealed tantalum tube at 1320 K followed by slow cooling to 970 K. EuAuSn crystallizes with a pronounced subcell of space group Imma (KHg2 type). Additional very weak reflections required a quintupled b axis. The superstructure was refined from single-crystal four-circle diffractometer data (Imm 2, a = 479.1(1) pm, b = 3833.6(5) pm, c = 820.1(1) pm, Z = 20, wR2 = 0.0834, 3675 F2 values and 94 variables). Six crystallographically different europium sites occur in the superstructure. Each europium site has an ordered near-neighbour environment of six gold and six tin atoms in the form of two tilted hexagons. Magnetic susceptibility measurements show Curie-Weiss behaviour above 50 K with an experimental magnetic moment of 7.6(1) μB/Eu, indicating divalent europium. EuAuSn orders antiferromagnetically at about 12 K and undergoes a metamagnetic transition at a critical field of 2.0(2) T. Electrical conductivity measurements show metallic behaviour with a room temperature value of 260 μΩcm. 151Eu and 119Sn Mössbauer spectroscopic experiments are compatible with divalent europium and show complex magnetic hyperfine field splitting at low temperature.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031118
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  • 7
    Digitale Medien
    Digitale Medien
    Electronic and Geometrical Structures of Dialuminoxane, Diboroxane, and Their Sulfur Analogues: Ab Initio Study of H2X-Y-XH2 (X = Al, B; Y = O, S) Compounds (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1860-1865 
    Details
    ISSN: 0947-6539
    Schlagwort(e): ab initio calculations ; aluminum ; boron ; pi interactions ; sulfur ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The structures of H2X—Y—XH2 compounds (X = B, Al; Y = O, S) have been studied by means of ab initio calculations at the MP4/6-311 G**/MP2/6-311G** level. The potential energy surface (PES) of the aluminoxane species H2Al—O—AlH2 is rather flat: the energy differences between the various located extrema are less than 1.5 kcal mol-1, and this shows that the observed geometrical preference is not due to electronic factors. For the sulfur analogues H2X—S—XH2 (X = B, Al), three minima are located on the PES: a planar C2v structure, a Cs structure in which one hydrogen atom bridges the two X atoms, and a C2v structure with two bridging hydrogen atoms. For H2Al—S—AlH2, the Cs structure is the most stable, and the planar C2v and the dibridged structures lie 3.2 and 6.7 kcal mol-1 higher, respectively. Qualitatively similar results are obtained for H2B—S—BH2: the Cs and planar C2v structures are nearly isoenergetic, and the dibridged minimum lies 19.4 kcal mol-1 above the planar C2v minimum. These results are rationalized by analyzing the ability of these systems to bend, depending on the nature (oxygen or sulfur) of the central Y atom. The conjugation in these species is also discussed, and calculations on model systems H2X—YH (X = B, Al; Y = O, S) are presented.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031119
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  • 8
    Digitale Medien
    Digitale Medien
    Stoichiometric and Catalytic Reactions of the Polysiloxane-Bound (Ether-Phosphine)Rhodium(I) Complex [ClRh(PO)(P ∼ O)] in InterphasesSupported organometallic complexes part 14. Part 13: E. Lindner, A. Jäger, F. Auer, W. Wielandt, P. Wegner, J. Mol. Catal. in press.Dedicated to Professor H. D. Kaesz on the occasion of his 65th birthdayNotation used in this paper: Fn = functionality; D, T, and Q denote alkoxysilanes with two, three, and four Si-O bonds, respectively; the superscript denotes the number of Si—O—Si bonds formed during the sol-gel process and is a measure of cross-linkage; for example, T0 = MeSi(OMe)3. P∼O: η1-P-coordinated ether-phosphine ligand; PO: η2-O,P-chelating ether-phosphine ligand. Cy = cyclohexyl, COE = cyclooctene, Py = pyridine. (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1833-1845 
    Details
    ISSN: 0947-6539
    Schlagwort(e): immobilized catalysts ; polysiloxanes ; P ligands ; rhodium ; sol-gel processes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reaction of four equivalents of the monomeric trimethoxysilyl(T)-functionalized ether-phosphine ligand CyP(CH2CH2OCH3)(CH2)3SiR3 (R = OMe [1 a(T0)], Me [1 b]) with [{μ-ClRh(COE)2}2] yielded the monomeric pseudo 14 electron rhodium(I) complexes [ClRh(PO)(P∼O)] (2a(T0)2, 2 b). For the sol-gel process the complex 2 a(T0)2 was protected by introduction of the volatile, reversibly binding ligand pyridine. Thus, the monomeric compound 2 a(T0)2 was co-condensed with two and eight equivalents of the co-condensation agent MeSi(OMe)2(CH2)6(MeO)2SiMe (D0-C6-D0) to give the polysiloxane-bound congeners 2(Tn)2(Di-C6-Di)y (y = 2 and 8, respectively; i = 0-2; n = 0-3). The polysiloxane-bound complex 2(Tn)2-(Di-C6-Di)2 was treated with a variety of small molecules in the gas/solid and liquid/solid interphases. It was shown that a facile cleavage of the Rh-O bond in the ether-phosphine chelate occurred even in the solid state. The reaction of 2(Tn)2-(Di-C6-Di)2 with carbon monoxide, carbon disulfide, and diphenylacetylene resulted in the irreversible coordination of the molecule to the metal. In the presence of pyridine, the polysiloxane-bound complex 2(Tn)2-(Di-C6-Di)2 oxidatively added hydrogen to give the octahedrally configurated complex [ClRhH2(Py)(P ∼ O)2] [6(Tn)2(Di-C6-Di)2]. Treatment of dry 2(Tn)2-(Di-C6-Di)2 with ethene led to the reversible formation of the corresponding complex. Although the materials display low surface areas, at least 75% of the rhodium centers within the matrix are accessible to the rather bulky tolan molecules. The complexes 2(Tn)2(Di-C6-Di)y (y (y = 2, 8) show high activities and selectivities in the hydrogenation of tolan. The conversion was found to depend markedly on the amount of co-condensate (D0-C6-D0) and on the polarity of the solvent. The polysiloxane-bound complexes 2(Tn)2(Di-C6-Di)y are more active than their monomeric congener 2 a(T0)2.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031116
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  • 9
    Digitale Medien
    Digitale Medien
    A Study of the Gas-Phase Reactivity of Neutral Alkoxy Radicals by Mass Spectrometry: α-Cleavages and Barton-type Hydrogen MigrationsDedicated to Sir Derek H. R. Barton (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1866-1883 
    Details
    ISSN: 0947-6539
    Schlagwort(e): alkoxy radicals ; Barton reaction ; density functional calculations ; mass spectrometry ; radicals ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reactivity of neutral alkoxy radicals in the absence of any interfering intermolecular interactions is investigated by means of the recently introduced method of neutral and ion decomposition difference (NIDD) spectra. These are obtained from quantitative analysis of the corresponding neutralization-reionization (NR) and charge reversal (CR) mass spectra. The following trends emerge: alkoxy radicals with short (C1—C3) or branched alkyl chains give rise to α-cleavage products, whereas longer-chained alkoxy radicals undergo 1,5-hydrogen migrations from carbon to oxygen, that is, Barton-type chemistry. This facile rearrangement has been studied in detail for n-pentoxy radicals by isotopic labeling experiments and computation at the Becke 3 LYP/6-31 G* level of theory. Further, the NIDD spectra of 3-methylpentoxy radicals permit for the first time the identification of the diastereoselectivity of the gas-phase hydrogen migrations. The results from the NIDD method are compared to those from earlier studies in the condensed phase. This new mass spectrometric approach is suggested as a tool for the examination of intramolecular reactions of free alkoxy radicals which can usefully complement theoretical studies.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031120
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  • 10
    Digitale Medien
    Digitale Medien
    Asymmetric Addition Reactions with Optimized Selenium Electrophiles (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1894-1902 
    Details
    ISSN: 0947-6539
    Schlagwort(e): asymmetric synthesis ; chirality ; diselenides ; selenium ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis of various nonracemic diselenides by different methods is described. These diselenides are precursors for optically active selenium electrophiles. Their facial selectivity upon addition to styrene was investigated with respect to the chiral moiety neighboring the selenium. Diselenides 1 i, 1 n, and 1 v yielded addition products 7 with diastereomeric excesses up to 95%. Some diselenides, intermediates, and products of the addition reaction were investigated by 77Se NMR spectroscopy.
    Zusätzliches Material: 2 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031123
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  • 11
    Digitale Medien
    Digitale Medien
    2,3,7,8,12,13,17,18-Octafluoro-5,10,15,20-Tetraphenylporphyrin: First Synthesis and X-Ray Crystal Structure of the ZnII Complex (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1890-1893 
    Details
    ISSN: 0947-6539
    Schlagwort(e): heterocycles ; fluorine ; porphyrinoids ; zinc ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 2,3,7,8,12,13,17,18-Octafluoro-5,10,15,20-tetraphenylporphyrin has been prepared from 3,4-difluoropyrrole and benzaldehyde under Lindsey conditions. An X-ray crystal structure study of its ZnII complex has shown that the macrocycle core is nonplanar, a result in apparent contradiction with a blue-shifted UV/Vis spectrum. The results reported here demonstrate that a wide range of β-octafluoro-meso-arylated porphyrins, a new class of highly electron-deficient ligands, are potentially accessible from 3,4-difluoropyrrole, thus opening the door to, inter alia, efficient and robust oxidation catalysts.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031122
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  • 12
    Digitale Medien
    Digitale Medien
    Cover page (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. cpi 
    Details
    ISSN: 0947-6539
    Schlagwort(e): Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031201
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  • 13
    Digitale Medien
    Digitale Medien
    Structure and Properties of Ba6Ni25S27 (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1884-1889 
    Details
    ISSN: 0947-6539
    Schlagwort(e): conducting materials ; electronic structure ; magnetic properties ; phase transitions ; sulfur ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Ba6Ni25S27, synthesized by solid-state reaction of BaS, NiS, and Ni at 675°C, is cubic (Pm3m, a = 10.057(1) Å). The structure was refined by using powder X-ray diffraction and Rietveld methods with Rp = 6.28%, Rwp = 8.13%, χ2 = 3.120. The structure, isotypic with Ba6Co25S27, consists of an extended network of Ni8S14 pseudo-cube clusters, NiS6 octahedra, and Ba6S octahedra. Extended Hückel calculations of this compound indicate the band structure near the Fermi level to be composed mostly of d-character orbitals of tetrahedral Ni, and reveal a peak in the density of states slightly below the Fermi level. The temperature dependence of the electrical resistivity exhibits a local maximum with thermal hysteresis at around 230 K. Above and below this transition, the slope of the resistivity is positive, with a room-temperature resistivity (ρ = 0.23 mωcm) in the range for that of a poor metal conductor. Magnetic susceptibility measurements from 4 to 900 K indicate a sharp change in slope at around 225 K, with a steadily increasing susceptibility up to 900 K. The susceptibility below 225 K suggests Pauli paramagnetic behavior. Low-temperature powder X-ray diffraction and subsequent structure refinement shows that the lattice parameter, a, undergoes a slight change in slope at temperatures of around 235 K.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031121
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  • 14
    Digitale Medien
    Digitale Medien
    Masthead (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997) 
    Details
    ISSN: 0947-6539
    Schlagwort(e): Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031202
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  • 15
    Digitale Medien
    Digitale Medien
    Graphical abstract (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1911-1916 
    Details
    ISSN: 0947-6539
    Schlagwort(e): Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031203
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  • 16
    Digitale Medien
    Digitale Medien
    Metallic Hydrogen at High Pressures and Temperatures in JupiterFrom a lecture delivered at the meeting of the British Association for the Advancement of Science at the University of Birmingham, September 9-13, 1996. (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1921-1924 
    Details
    ISSN: 0947-6539
    Schlagwort(e): high-pressure chemistry ; high-temperature chemistry ; hydrogen ; Jupiter ; metallic hydrogen ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Electrical conductivities of hydrogen were measured recently at 93-180 GPa (0.93-1.8 Mbar), 0.28-0.36 mol cm-3, and 2000-4000 K. Shock temperatures were measured up to values of 5200 K at 0.83 Mbar. The conductivities indicate a continuous transition from a semiconducting to metallic fluid at 140 GPa and 3000 K. The results indicate that hydrogen becomes metallic much closer to the surface of Jupiter than thought previously and that Jupiter has no core-mantle boundary.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031205
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  • 17
    Digitale Medien
    Digitale Medien
    Drug Discovery by Combinatorial Chemistry - the Development of a Novel Method for the Rapid Synthesis of Single CompoundsFrom a lecture delivered at the meeting of the British Association for the Advancement of Science at the University of Birmingham, September 9-13, 1996. (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1917-1920 
    Details
    ISSN: 0947-6539
    Schlagwort(e): combinatorial chemistry ; compound libraries ; drug research ; solid-phase synthesis ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Through the advantages conferred in the speed of synthesis, combinatorial chemistry is making a significant impact on the process of drug discovery. The mix-and-split paradigm has been an effective method for the production of compound mixtures, although there is now a need for new, fast library approaches to generate well-characterised single compounds. Having already demonstrated the successful preparation and application of library mixtures, we have now developed a novel combinatorial method for the production of single compounds.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031204
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  • 18
    Digitale Medien
    Digitale Medien
    Molecules in SpaceFrom a lecture delivered at the meeting of the British Association for the Advancement of Science at the University of Birmingham, September 9-13, 1996. (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1929-1932 
    Details
    ISSN: 0947-6539
    Schlagwort(e): gas-phase chemistry ; interstellar chemistry ; ion-molecule reactions ; star formation ; surface chemistry ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The distribution and nature of interstellar matter in the Galaxy is described. The chemical processes by which the rich variety of molecular species arise are briefly sketched. The importance of interstellar molecules in influencing the evolution of the Galaxy is emphasized.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031207
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  • 19
    Digitale Medien
    Digitale Medien
    Gas-Phase Reactions at Low Temperatures: Towards Absolute ZeroFrom a lecture delivered by I. W. M. S. at the meeting of the British Association for the Advancement of Science at the University of Birmingham, September 9-13, 1996. (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1925-1928 
    Details
    ISSN: 0947-6539
    Schlagwort(e): gas-phase chemistry ; interstellar chemistry ; kinetics ; low-temperature chemistry ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Very recently, methods have been developed for studying the rates of chemical reactions between electrically neutral species in the gas phase at temperatures as low as 13 K. Here we review this exciting development in gasphase chemical kinetics. Emphasis is placed on the importance of the information which the experiments have provided, both from the viewpoint of posing new questions about the factors which control chemical reactivity and because of their relevance to the modelling of molecular synthesis in interstellar clouds.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031206
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  • 20
    Digitale Medien
    Digitale Medien
    Opposite Stereochemical Effects Exerted by CeCl3 and TiCl4 on the Lewis Acid Mediated Reduction of α-Alkyl-β-ketophosphine Oxides with Metallic Hydrides: A Highly Stereoselective Protocol for the Synthesis of syn and anti α-alkyl-β-Hydroxyphosphine Oxides (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1941-1950 
    Details
    ISSN: 0947-6539
    Schlagwort(e): alkenes ; asymmetric synthesis ; natural products ; Lewis acids ; phosphane oxides ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A general, highly efficient methodology for obtaining both syn and anti β-hydroxyphosphine oxides by reduction of the corresponding β-ketophosphine oxides is described. The nature of the Lewis acid was found to be pivotal in determining the outcome of these reactions. Strongly chelating TiCl4 led to the anti isomer in high diastereoisomeric excess in noncoordinating solvents (CH2Cl2) at -78°C with BH3/py as reducing agent, while nonchelating CeCl3 gave a high excess of the syn isomer in coordinating solvents (THF) at the same temperature with LiBH4 as reducing agent. In the latter case, CeCl3 is essential in achieving high yields and stereoselectivity, since it allows the reaction to be performed at low temperatures. Otherwise, higher temperatures (0°C) are required, which lower both yields and selectivities. Moreover, each step of the protocol for the synthesis of stereodefined disubstituted olefins from alkylphosphine oxides (Warren's modification of the Horner procedure) has been optimized, and the optimized procedure has been applied to the synthesis of muscalure, the pheromone of the domestic fly.
    Zusätzliches Material: 4 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031209
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  • 21
    Digitale Medien
    Digitale Medien
    Total Synthesis of Oxazole- and Cyclopropane-Containing Epothilone A Analogues by the Olefin Metathesis Approach (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1957-1970 
    Details
    ISSN: 0947-6539
    Schlagwort(e): epothilone ; oxazoles ; cyclopropanes ; metathesis ; total synthesis ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: For structure-activity relationship studies, two series of epothilone A (1) analogues have been designed and synthesized, one containing an oxazole moiety instead of the thiazole heterocycle and the other containing a spirocyclopropane moiety in place of the gem-dimethyl group at position C-4 (4,4-ethano-epothilones). The olefin metathesis strategy in solution was utilized for the chemical synthesis of these compounds starting with key building blocks 7-9 for the oxazole series (compounds 2, 14-18, 21-26) and building blocks 8, 30, and 31 for the 4,4-ethano series (compounds 3,39-43, 46-51). The convergent strategy towards the designed epothilone A series involved a) an aldol condensation reaction, b) an esterification reaction, c) an olefin metathesis reaction catalyzed by [RuCl2(=CHPh)-(PCy3)2], and d) epoxidation of the macrocycle double bond.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031211
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  • 22
    Digitale Medien
    Digitale Medien
    Controlling Self-AssemblyFrom a lecture delivered by J. F. S. at the meeting of the British Association for the Advancement of Science at the University of Birmingham, September 9-13, 1996. This paper is Part 26 in the series “Molecular Meccano” for Part 25, see S. Menzer, A. J. P. White, D. J. Williams, M. Belohradsky, C. Hamers, F. M. Raymo, A. N. Shipway, J. F. Stoddart, Macromolecules, in press. (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1933-1940 
    Details
    ISSN: 0947-6539
    Schlagwort(e): catenanes ; molecular recognition ; pseudorotaxanes ; supramolecular chemistry ; translational isomerism ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: As a result of cooperative noncovalent bonding interactions (namely, π-π stacking, [CH…O] hydrogen bonding, and [CH…π] interactions) supramolecular complexes and mechanically interlocked molecular compounds - in particular pseudorotaxanes (precatenanes) and catenanes - self-assemble spontaneously from appropriate complementary components under thermodynamic and kinetic control, respectively. The stereoelectronic information imprinted in the components is crucial in controlling the extent of the formation of the complexes and compounds in the first place; moreover, it has a very significant influence on the relative orientations and motions of the components. In other words, the noncovalent bonding interactions - that is, the driving forces responsible for the self-assembly processes - live on inside the final superstructures and structures, governing both their thermodynamic and kinetic behavior in solution. In an unsymmetrical [2]catenane, for example, changing the constitutions of the aromatic rings or altering the nature of substituents attached to them can drive an equilibrium associated with translational isomerism in the direction of one of two or more possible isomers both in solution and in the solid state. Generally speaking, the slower the components in mechanically interlocked compounds like catenanes and rotaxanes move with respect to each other, the easier it is for them to self-assemble.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031208
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  • 23
    Digitale Medien
    Digitale Medien
    Gold Clusters and Colloids in Alumina NanotubesDedicated to Professor Achim Müller on the occasion of his 60th birthday (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1951-1956 
    Details
    ISSN: 0947-6539
    Schlagwort(e): clusters ; colloids ; gold ; nanostructures ; quantum wires ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The fabrication of a supported and insulated quantum wire would be of great interest, especially if electronic information could be accessed to determine charging and conductivity profiles. The feasibility of forming one-dimensional configurations of ≈ 15 nm gold colloids and 1.4 nm gold clusters via template methods of synthesis has now been demonstrated. The template host material consisted of porous alumina membranes formed by an electrochemical anodic process. The pores of the membrane, and hence the parallel pore channels, were packed in a hexagonal array. Alumina membranes are excellent template materials because of their high degree of order, thermal and chemical stability, and optical clarity. Pore diameter was controlled by regulation of the applied anodic potential (ca. 1.4 nm V-1). The pore channels were filled by one of three methods: vacuum induction (colloids only), electrophoresis (clusters only), or immersion (clusters, which were then converted into colloids by heating). Rudimentary wires consisting of colloids and clusters were successfully formed. In both cases, the diameter of the pore channel exceeded that of the clusters or colloids. The wires thus formed conformed to the pore channel by forming helical secondary structures. It was not possible to form contiguous wires of clusters by immersion, or of colloids formed from clusters after heating. Composites (consisting of the gold-alumina system) were a bright scarlet color with an absorption maximum (λmax) at 519.5 nm. This is an unexpected result for spherical and small-diameter (10 nm) gold colloids, which normally absorb at λmax 525-530 nm, a ruby-red color. Possible causes of this small but remarkable blue shift are discussed below. A new Au55 cluster ligand system consisting of a silsesquioxane-derivatized thiol is also described.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031210
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  • 24
    Digitale Medien
    Digitale Medien
    Total Synthesis of Oxazole- and Cyclopropane-Containing Epothilone B Analogues by the Macrolactonization Approach (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1971-1986 
    Details
    ISSN: 0947-6539
    Schlagwort(e): epothilone ; oxazoles ; cyclopropanes ; total synthesis ; macrolactonizations ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In order to probe structure-activity relationships in the epothilone area, two series of epothilone B analogues have been designed and synthesized. The first series containing an oxazole moiety in place of a thiazole on the side chain was constructed by utilizing key intermediates 7-9 or 10, 12, and 13 (Scheme 1), whereas the second series containing an ethano group instead of the gem-dimethyl group at position 4 was synthesized from fragments 42 and 43. A Yamaguchi-type macrolactonization reaction was used to construct the macrocycle from a secoacid, which was assembled, in both cases, by means of a) an aldol reaction, b) an Enders alkylation, and c) a Wittig-type reaction. This convergent strategy provided access to oxazole analogues 2,4,29-32 and 4,4-ethano derivatives 3,40,60-63 for biological studies.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031212
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  • 25
    Digitale Medien
    Digitale Medien
    Polymeric [(Me3Sn)3Rh(SCN)6]: A Novel “Super-Prussian-Blue” Derivative Containing the Nonlinear -SCN-Sn-NCS- SpacerDedicated to Professor Gottfried Huttner on the occasion of his 60th birthday (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1987-1991 
    Details
    ISSN: 0947-6539
    Schlagwort(e): coordination polymers ; Prussian blue ; rhodium ; structure elucidation ; tin ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The new coordination polymer [(Me3SnIV)3RhIII(SCN)6] = 3∞[Rh{μ-(SCNSnMe3NCS)}3] (5) is readily accessible by straightforward self-assembly of [Rh(SCN)6]3- and (dehydrated) {Me3Sn}+aq ions. The architecture of 5 is strongly reminiscent of “super-Prussian-blue” systems reported earlier: there is a three-dimensional (3-D) framework involving {Rh8} pseudocubes as the basic building blocks, the Rh3+ ions being held apart by novel, nonlinear {SCN-SnMe3-NCS} spacers (d(Rh…Rh) = 1.27 nm). The complete lattice consists of two equivalent and independent, ideally interwoven 3-D frameworks. Three homologues of 5 with slightly modified R3Sn units (R = Et, nPr and nBu) have been prepared as well, but display X-ray powder diffraction patterns notably different from that of 5.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031213
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  • 26
    Digitale Medien
    Digitale Medien
    Electrochemically Induced Molecular Motions in Pseudorotaxanes: A Case of Dual-Mode (Oxidative and Reductive) Dethreading (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1992-1996 
    Details
    ISSN: 0947-6539
    Schlagwort(e): cyclic voltammetry ; logic gates ; molecular devices ; pseudorotaxanes ; spectroelectrochemistry ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The electrochemical and spectroscopic properties of a pseudorotaxane formed in acetonitrile solution by self-assembly of a wire-type electron donor based on the tetrathiafulvalene unit and the cyclobis(paraquat-p-phenylene) tetracationic electron acceptor have been investigated. We show that a) reversible dethreading/rethreading cycles of the pseudorotaxane can be performed by either oxidation and successive reduction of the electron-donor wire or reduction and successive oxidation of the electron-accepting tetracationic cyclophane, and b) because of this special behavior, the input (electrochemical)/output (absorption spectrum) characteristics of this molecular-level system correspond to those of an XNOR logic gate.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031214
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  • 27
    Digitale Medien
    Digitale Medien
    Oligonucleotide Analogues with 4-Hydroxy-N-Acetylprolinol as Sugar Substitute (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1997-2010 
    Details
    ISSN: 0947-6539
    Schlagwort(e): antisense agents ; chiral recognition ; oligonucleotides ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Modified oligonucleotides incorporating trans-4-hydroxy-N-acetyl-L-prolinol (trans-4-HO-L-NAP) or its D-analogue as sugar substitute were synthesised with adenine and thymine as nucleobases. All-adenine oligonucleotides built from (2S,4S) or (2R,4R)-cis-4-hydroxy-N-acetylprolinol were likewise prepared. Hybridisation studies revealed that heterocomplexes formed between polyU and homochiral trans-4-hydroxy-N-acetylprolinol-based oligomers of the same as well as of opposite chirality (polyU/trans-DA*13 and polyU/trans-LA*13). The former, however, were triple-stranded. Other complexes with ribonucleic acids were polyA/trans-LT*13 and polyU/cis-LA*13. Heteroduplexes with deoxynucleic acids were formed between trans-LA*13 and oligothymidylate. Interaction was also observed for cis-LA*13 and oligothymidylate, but not with the D-hydroxyprolinol analogues. Microcalorimetry proved this interaction to be the formation of a triple-stranded complex. Two heteroduplexes, trans-LA*13/dT13 and trans-LA*13/polyU, had similar or slightly increased stability when compared to the natural dA13/dT13 or dA13/polyU systems. Microcalorimetry clearly indicated the formation of a duplex, in contrast to interactions with N-acetylprolinol oligonucleotides of different stereochemistry. Moreover, the enthalpy change was of the same magnitude but the association constant was slightly lower. Natural nucleic acids thus clearly prefer hybridisation with L-hydroxyprolinol oligomers over D-hydroxyprolinol oligomers. For the series investigated, the L-trans oligomers (Figure 1) seem best to mimic natural oligonucleotides. These modified oligonucleotides formed homocomplexes if both strands were of the same chirality, that is, homocomplexes formed between trans-LA* and trans-LT* and between trans-DA* and trans-DT*, reflecting the isochiral pu-py pairing found in natural nucleic acids. Once more, however, calorimetry proved these to be triplex interactions. Heterochiral pairing was not observed between modified oligonucleotides, but only between modified oligonucleotides and natural polyU. The thermal stabilities of these heterochiral complexes differed clearly.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031215
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  • 28
    Digitale Medien
    Digitale Medien
    Rapid Coupling of Methyl Iodide with Aryltributylstannanes Mediated by Palladium(0) Complexes: A General Protocol for the Synthesis of 11CH3-Labeled PET Tracers (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 2039-2042 
    Details
    ISSN: 0947-6539
    Schlagwort(e): arylphosphanes ; C-C coupling ; isotopic labeling ; palladium ; tin ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reaction of methyl iodide and (excess) aryltributylstannane to give a methylarene has been studied with the focus on the realization of rapid coupling for incorporation of short-lived radionuclides into bioactive organic compounds. The coupling of methyl iodide with tributylphenylstannane (40 equiv) is accomplished in 〉90% yield within 5 min at 60°C with a tri-o-tolylphosphine-bound, coordinatively unsaturated Pd0 complex together with a CuI salt and K2CO3 in DMF. This protocol is applicable to a variety of homo- and heteroaromatic tin compounds, to give the corresponding methylated derivatives. The effects of the tri-o-tolylphosphine ligand, a Cu(I) salt, and DMF are discussed. This new protocol provides a firm chemical basis for the synthesis of 11CH3-incorporated PET tracers.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031219
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  • 29
    Digitale Medien
    Digitale Medien
    Some Remarks on the Occurrence and Properties of Knödel (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 2081-2081 
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    ISSN: 0947-6539
    Schlagwort(e): carbohydrates ; correspondence ; dendrimers ; micelles ; nanospheres ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031225
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  • 30
    Digitale Medien
    Digitale Medien
    Mechanisms and Stereochemistry of Acid-Induced Ring Opening of Optically Active 1,2-Propene Oxides in the Gas PhaseChiral ions in the gas phase, part 3. Parts 1 and 2: ref. [1]. (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 2063-2070 
    Details
    ISSN: 0947-6539
    Schlagwort(e): chirality ; gas-phase chemistry ; ion-molecule reactions ; regioselectivity ; ring-opening reactions ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The acid-induced ring opening of (S)-( - )-1,2-propene oxide (1S) and (R)-(+)-1,2-propene oxide (1R) has been investigated in gaseous CH4 and CH3F at 720 torr and in the presence of a nucleophile, NuOH (Nu = H or CH3). The mechanism of the ring-opening reaction has been assessed by modulating the composition of the gaseous mixture. Two reaction pathways are operative in the gas phase, both proceeding through complete inversion of configuration of the reaction center. A first process is detectable only in the CH3F/H2O systems and takes place within a persistent proton-bound complex generated by interaction of the epoxide with the CH3OH+2 ion, formed by methylation of H2O with (CH3)2F+. Such an intracomplex ring-opening pathway proceeds through proton transfer from the CH3OH+2 ion to the epoxide followed by motion of the neutral CH3OH moiety around the 1-H-oxonia-2-methyl-cyclo-propane structure (H-1R or H-1S) (k〈108 s-1) before attacking the ring carbons from the rear. In all the other systems with added CH3OH, this intracomplex pathway is preceded by a faster “extracomplex” pathway involving the attack of an external CH3OH molecule on the proton-bound adduct. The regioselectivity of the intracomplex process is similar to that of the extracomplex pathway. Both are characterized by a slight preference for the Cβ center of H-1 R (or H-1S) (extra-complex path regioselectivity: α/β = 0.72±0.05; intracomplex path regioselectivity: α/β = 0.71±0.05). The regioselectivity of H-1 R (or H-1S) is substantially different from that of the 1-Me-oxonia-2-methyl-cyclopropanes (Me-1 R or Me-1 S) toward the same nucleophile NuOH (α/β = 4.1±0.35 (Nu = H); 2.28±0.16 (Nu = CH3)). This difference is attributed to a transition structure wherein the Cα-O bond rupture increases from H-1 R (or H-1 S) to Me-1 R (or Me-1 S) and in passing from CH3OH to H2O. The regioand stereoselectivity of the gas-phase acid-induced ring opening of 1 S and 1 R are compared with those of related reactions carried out in solution.
    Zusätzliches Material: 3 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031223
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  • 31
    Digitale Medien
    Digitale Medien
    Reaction of „Jordan′s Cation“ [Cp2ZrCH3(thf)]+ with Amino Acid-Derived Isocyanates - A First Synthetic Route to Oligopeptide-Modified Group 4 Bent Metallocene Cation SystemsDedicated to Professor Waldemar Adam on the occasion of his 65th birthday (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1521-1525 
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    ISSN: 0947-6539
    Schlagwort(e): isocyanates ; „Jordan′s cation“ ; metallocenes ; peptides ; zirconium ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The organometallic cation [Cp2ZrCH3(thf)]+, employed as the tetraphenylborate salt (1), reacts cleanly in 1:1 stoichiometry with the isocyanates 2 derived from valine methyl ester or valylvaline methyl ester, respectively. In each case addition of the Zr-CH3 group to the isocyanate sp-carbon center is observed with formation of a functionalized zirconocene cation derivative containing a chelating N-metallated N-acetylvaline methyl ester (3a) or N-acetylvalylvaline methyl ester (3b) moiety, respectively, coordinated in the bent metallocene s̰-ligand plane. The spectroscopic data of 3, supported by an X-ray crystal structure analysis of the zirconated dipeptide derivative 3b, have revealed the presence of chelating (η1-O:η1-N)-coordination of the terminal N-acetyl groups in addition to a Zr-O=C interaction with the adjacent valyl amido group.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970030921
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  • 32
    Digitale Medien
    Digitale Medien
    Cover page (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. cpi 
    Details
    ISSN: 0947-6539
    Schlagwort(e): Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031001
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  • 33
    Digitale Medien
    Digitale Medien
    Masthead (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997) 
    Details
    ISSN: 0947-6539
    Schlagwort(e): Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031002
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  • 34
    Digitale Medien
    Digitale Medien
    Formal [4 + 3], [4 + 2], [4 + 1] cycloadditions and acid-base reaction of 2-methyl-1,3-dimorpholino-1,3-butadiene with Fischer carbene complexes (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1629-1637 
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    ISSN: 0947-6539
    Schlagwort(e): C-H activation ; carbene complexes ; cycloadditions ; 1,3-diamino-1,3-butadiene ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 2-Methyl-1,3-dimorpholino-1,3-butadiene 1 reacted with α,β-unsaturated Fischer carbene complexes to give a wide range of different products depending on the substitution pattern. Thus, sevenmembered rings (4, 5 and 6) could be obtained from chromium complexes 2 with aromatic or vinylic groups at the β position. Similar results were observed when α-methyl-substituted carbene complex 7 a was used. Six-membered carbocycles (derivatives of cycloadducts 12 and 13) were isolated after reaction with both chromium and tungsten complexes bearing one or two alkyl groups at the β position (10 and 11). Moreover, cyclopentenones 20 were the main products when the starting carbene complexes were alkyl-substituted at both α and β positions (19a, b) or when aromatic (19c, d) instead of vinylic complexes were used. A bicyclo[4.1.0]heptene system 18 has also been obtained in the special case of reaction with β,β-dimethylvinylchromium complex 13b; its formation could be explained as a formal carbene insertion into a C-H bond. The behaviour of diene 1 towards alkoxymethylcarbene complexes 22 was unusual. The different reaction products (cyclopentadienes 23, bicyclo[3.1.0]hexenes 24, aromatic amine 25 and metallatrienes 26) imply a mechanism in which the deprotonation of the carbene complex by the diene is followed by Michael addition to the iminium salt formed.
    Zusätzliches Material: 5 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031012
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  • 35
    Digitale Medien
    Digitale Medien
    In Search for Mononuclear Helical Lanthanide Building Blocks with Predetermined Properties: Triple-stranded Helical Complexes with N,N,N',N'-tetraethylpyridine-2,6-dicarboxamide (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1646-1659 
    Details
    ISSN: 0947-6539
    Schlagwort(e): carboxamides ; helical structures ; lanthanides ; luminescence ; tridentate ligands ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The ligand N,N,N',N'-tetra-ethylpyridine-2,6-dicarboxamide (L9) reacts with trivalent lanthanide ions (LnIII) to give stable mononuclear triple-stranded helical complexes [Ln(L9)3]3+ (Ln = La to Lu). The crystal and molecular structures of [La(L9)3](ClO4)3.2.5C2H5CN (8) and [Eu(L9)3](TfO)3.2THF (9) show that the three ligand strands are each meridionally tricoordinated to produce a pseudo-tricapped trigonal prismatic arrangement of the nine donor atoms (six amide O and three pyridine N) around LnIII. The distortions in the LaIII coordination sphere of 8 are more significant than for EuIII in 9, and the photophysical studies on Eu-doped (2%) La, Gd, and Lu complexes confirm a better structural match of L9 for the heavy LnIII ions. The separation of contact and pseudo-contact contributions to the induced lanthanide paramagnetic NMR shifts in [Ln(L9)3]3+ shows that the triple-helical structure is maintained in acetonitrile, but a minor structural change relative to that observed in the solid state occurs between TbIII and ErIII leading to two distinct isostructural series for Ln = La-Tb and Ln = Er-Lu. The origin of this effect together with its consequences for the dynamic helical (P→M) interconversion and stability of [Ln(L9)3]3+ in solution are discussed. A detailed investigation of the emission properties of [Ln(L9)3]3+ (Ln = Eu, Tb) shows that mixed pyridine-carboxamide ligands can be used to simultaneously optimize the structural and photophysical properties in mononuclear triple-helical lanthanide building blocks.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031014
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  • 36
    Digitale Medien
    Digitale Medien
    Type B Semiconductor Photocatalysis: The Synthesis of Homoallyl Amines by Cadmium Sulfide-Catalyzed Linear Photoaddition of Olefins and Enol/allyl Ethers to N-Phenylbenzophenone ImineHeterogeneous Photocatalysis, part XVI. Part XV: W. Schindler, H. Kisch, J. Photochem. Photobiol. A: Chem., 1997, 103, 257. (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1638-1645 
    Details
    ISSN: 0947-6539
    Schlagwort(e): cadmium sulfide ; catalysis ; photochemistry ; semiconductors ; unsaturated amines ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Homoallyl amines were synthesized by visible-light irradiation of CdS powder in the presence of N-phenylbenzophenone imine and cyclohexene, 2,3-dihydrofuran, 2,5-dihydrofuran, 3,4-dihydropyran, 2-pentene, cyclopentene, 1-methylcyclohexene, or α-pinene. The structures of the products from the last three olefins were determined by single-crystal X-ray analysis to prove that C-alkylation of the imine had occurred. Thus, the reaction is formally an insertion of the imine into an allylic C-H bond of the olefin. It is proposed that a photogenerated electron-hole pair reduces the imine to an α-aminodiphenylmethyl radical and oxidizes the olefin with concomitant deprotonation to the corresponding allyl radical. Heterocoupling of these intermediates affords the final addition product. The overall reaction is therefore classified as type B semiconductor photocatalysis. The presence of acetic acid accelerates the reaction by rendering the reduction potential of the imine more positive. In the series 2,5-dihydrofuran/cyclopentene/3,4-dihydropyran, the decrease in apparent quantum yield with increasing driving force of olefin oxidation points to a significant contribution of secondary back electron transfer.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031013
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  • 37
    Digitale Medien
    Digitale Medien
    A Highly Convergent Total Synthetic Route to Glycopeptides Carrying a High-Mannose Core Pentasaccharide Domain N-linked to a Natural Peptide Motif (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1617-1628 
    Details
    ISSN: 0947-6539
    Schlagwort(e): glycals ; glycopeptides ; glycosylations ; β-mannosides ; oligosaccharides ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: N-Linked glycopeptides were synthesized by condensation of a highmannose anomeric amine bearing a pentasaccharide with aspartic-acid-containing tri- and pentapeptides through the agency of IIDQ. The pentasaccharide portion, corresponding to the „core“ region of all asparagine-linked glycoproteins, was assembled by means of glycal-derived thioethyl donors and glycal acceptors. The central mannose residue was established by inversion of the C2 hydroxyl of a glucosyl precursor in the pentasaccharide. The protecting-group scheme employed allows the extension of the pentasaccharide through the terminal mannose units. While a fully convergent coupling of the high-mannose carbohydrate to the peptide domain has thus been accomplished for the first time with a fully synthetic sugar, the stereochemical integrity of the anomeric center of the carbohydrate domain was not maintained and a mixture of glycopeptides was obtained.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031011
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  • 38
    Digitale Medien
    Digitale Medien
    A Square As4 and a Prismatic As6 Structure as Complex Ligands (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1494-1498 
    Details
    ISSN: 0947-6539
    Schlagwort(e): arsenic ; cobalt ; density functional calculations ; structural elucidation ; Zintl anions ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: [As7(SiMe3)3] reacts with [(Cp*CoCl)2] to give black crystals of the ionic compound [(Cp*Co)3As6][CoCl4] (1). The cation [(Cp*Co)3As6]2+ consists of an As6 prism, with squares capped by [Cp*Co] fragments. When [(CptBuCoCl)2] is used instead of [(Cp*CoCl)2] in the reaction, dark red crystals of [(CptBuCo)3As6][CoCl3(thf)]2 (2) and green-black crystals of [(CptBuCo)2As4][Co3Cl8(thf)2] (3) can be obtained. The cation in 2 shows a structure very similar to that of 1. The [(CptBuCo)2As4]2+ cations in 3 can be described as a triple-decker sandwich complex with two [CptBuCo]+ fragments bridged by an As4 ligand. Density functional calculations reproduce the experimental data of 1 and 3 and allow an interpretation of molecular electronic structure and bonding in these and related compounds with As replaced by P and Co by Fe.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970030917
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  • 39
    Digitale Medien
    Digitale Medien
    1′,5′-Anhydrohexitol Oligonucleotides: Hybridisation and Strand Displacement with Oligoribonucleotides, Interaction with RNase H and HIV Reverse Transcriptase (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1513-1520 
    Details
    ISSN: 0947-6539
    Schlagwort(e): duplex ; gel mobility ; nucleic acids ; oligonucleotides ; strand displacement ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Hexitol nucleic acids (HNAs) with four natural bases form stable and sequence-selective duplexes with RNA. This was investigated by Tm determinations and gel shift experiments. The CD spectra of an HNA-RNA duplex show similarities with the CD spectra of the A-form of dsRNA. Single-stranded HNAs are able to induce strand displacement in a double-stranded RNA sequence. An HNA-RNA duplex is a poor substrate for RNase H, and can inhibit the RNase H-mediated cleavage of a natural DNA-RNA substrate. The HNA-RNA hybrid enhances the activity of HIV reverse transcriptase.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970030920
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  • 40
    Digitale Medien
    Digitale Medien
    Relaxometric Determination of the Exchange Rate of the Coordinated Water Protons in a Neutral GdIII Chelate (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1499-1504 
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    ISSN: 0947-6539
    Schlagwort(e): gadolinium ; NMR spectroscopy ; prototropic exchange ; rare earth compounds ; water exchange rate ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The exchange rate of the coordinated water molecule in the neutral complex [Gd(DTPA-BBA)(H2O)] (DTPA-BBA = 1,7-bis[(N-benzylcarbamoyl)methyl]-1,4,7-triazaheptane-1,4,7-triacetate or diethylenetriaminopentaacetate N,N′-bis(benzylamide)) is slower than in the parent complex [Gd(DTPA)(H2O)]2-. From the analysis of the temperature dependence of the solvent 17O NMR transverse relaxation time in an aqueous solution of the paramagnetic complex, a value of 4.5 × 105 s-1 (at 298 K) is obtained for the exchange rate of the coordinated water molecule. This rate constant does not vary in the pH range 7-12. Conversely, over the same pH range and at 298 K and 20 MHz, the longitudinal water proton relaxivity increases from 4.8 to 6.5 s-1 mM-1. The analysis of the dependence of the longitudinal water proton relaxation rate on magnetic field and temperature at pH 7 and pH 12 shows that the increase in relaxivity at basic pH has to be assigned to the contribution of the prototropic exchange at the water molecule in the inner coordination sphere of the metal ion. This exchange process is catalyzed by OH- ions (kP = 1.7 × 109 M-1 s-1 at 298 K) and causes an increase in the observed relaxivity when it occurs at a rate larger than the exchange rate of the entire water molecule. At pH 12 the limiting effect of the slow exchange rate for the coordinated water molecule is removed, and the longitudinal water proton relaxivity measured at this pH then represents the maximum value attainable for this complex.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970030918
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  • 41
    Digitale Medien
    Digitale Medien
    Poly(triacetylene) Oligomers: Synthesis, Characterization, and Estimation of the Effective Conjugation Length by Electrochemical, UV/Vis, and Nonlinear Optical MethodsDedicated to Professor Dieter Seebach on the occasion of his 60th birthday (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1505-1512 
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    ISSN: 0947-6539
    Schlagwort(e): conjugation length ; electrochemistry ; nonlinear optics ; oligomers ; poly-(triacetylene)s ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Poly(triacetylene)s [PTAs, —(C≡C—CR=CR—C≡C)n-] are a new class of linearly conjugated polymers with a nonaromatic all-carbon backbone. To explore structure-property relationships in PTAs, we prepared a series of monodisperse oligomers ranging from monomer to hexamer by oxidative Glaser-Hay coupling of a bifunctional („chain-forming“) (E)-hex-3-ene-1,5-diyne in the presence of an endcapping unit. All six oligomers are amazingly stable towards exposure to light, air, and temperatures beyond their melting points. They have been fully characterized and are readily soluble in a wide range of solvents. The conjugated rods are reversibly reduced in one-electron transfer steps and cannot be oxidized below +1.23 V vs. Fc/Fc+. The effective conjugation length in PTAs was estimated from the electronic absorption (UV/Vis) data, and various evaluation methods yielded convergence of the optical properties in the range of 7 to 10 monomer units. The nonresonant second-order molecular hyperpolarizability γ was measured in CHCl3 by means of the third harmonic generation (THG) at Δ = 1.907 μm. A plot of γ/n vs. n revealed a power law γ ≈ na for γ with a fitted exponent a = 2.5 ∓ 0.1. From the THG measurements, an effective conjugation length of about 10 monomer units was found, in surprisingly good agreement with the value obtained from UV/Vis spectroscopy data.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970030919
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  • 42
    Digitale Medien
    Digitale Medien
    Graphical abstract (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1552-1556 
    Details
    ISSN: 0947-6539
    Schlagwort(e): Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031003
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  • 43
    Digitale Medien
    Digitale Medien
    The Ineluctable Need for in Situ Methods of Characterising Solid Catalysts as a Prerequisite to Engineering Active Sites (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1557-1562 
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    ISSN: 0947-6539
    Schlagwort(e): enzyme catalysis ; EXAFS spectroscopy ; heterogeneous catalysis ; synchrotron radiation ; X-ray absorption spectroscopy ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Ultimate success in the design of solid oxide catalysts as well as other covalently bonded or heterogenised organometallic catalysts predicates knowledge of precisely what structure it is that has to be targetted. This, in turn, demands the greatest possible precision in determining, under operating conditions, the structure of the catalyst in general and of the active site in particular. Combined X-ray absorption spectroscopy and X-ray diffraction are ideal tools for such in situ investigations. Examples of such studies and of engineered catalysts, the structure of which have been determined in atomic detail, are given.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031004
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  • 44
    Digitale Medien
    Digitale Medien
    Strong Binding of Alkylguanidinium Ions by Molecular Tweezers: An Artificial Selective Arginine Receptor Molecule with a Biomimetic Recognition Pattern (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1537-1541 
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    ISSN: 0947-6539
    Schlagwort(e): arginine ; guanidines ; molecular recognition ; receptors ; supramolecular chemistry ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Bisphosphonates 2 and 3 represent the first artificial receptor molecules for alkylguanidinium ions. They bind to the guanidinium moiety by forming a 1:1 chelate complex, stabilized by a planar network of electrostatic interactions and hydrogen bonds. This hydrogen bonding configuration is identical to the „arginine fork“ postulated by Frankel as a key element in RNA-protein recognition of the AIDS virus. Our guanidinium-bisphosphonate complexes thus constitute the first synthetic model for this important biological interaction and demonstrate that the high binding energy can be a driving force for a conformational change in the receptor (induced fit, e.g., in the RNA). Although binding of monosubstituted alkylguanidines is generally strong (Ka ≈ 10 000 in DMSO), molecular tweezer 3 recognizes N- and C-amide-protected arginine derivatives especially well (Ka ≈ 300 000 in DMSO), because an additional hydrogen bond is formed between the amide and the phosphonate. Since 3 does not bind amines effectively, it is highly selective for arginine, even in the presence of lysine or other amino acids. For di-, tri-, and tetrasubstituted guanidines the association constant remains low (Ka≤1000 in DMSO) reflecting the increase in the steric bulk of the guest.
    Zusätzliches Material: 2 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970030923
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  • 45
    Digitale Medien
    Digitale Medien
    Chirality in Dendritic ArchitecturesThis concepts article is a personal reflection on the many issues raised by the combination of chirality and dendrimers. The concepts presented here are partly based on several recent reports in the published literature and partly on the highly appreciated discussions with colleagues on as yet undisclosed results. In particular Bert Meijer would like to express his gratitude to Professor Hans Wynberg who stimulated him to explore all aspects of stereochemistry.Dedicated to Professor Hans Wynberg on the occasion of his 75th birthday (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1563-1570 
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    ISSN: 0947-6539
    Schlagwort(e): catalysis ; chirality ; dendrimers ; molecular recognition ; surfaces ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: At first glance the topic of chiral dendrimers seems to be a contradiction in terms. However, recent studies reveal that both the building blocks of the dendrimer and the overall dendritic architecture can be chiral and that chirality can be introduced at various levels. The expression of optical activity in these enantiomerically pure dendrimers as a result of conformational (dis)order has proven to be of special interest. In this Concepts article we present the different approaches to introducing chirality in dendritic architectures, organized through their possible impact in fields such as biocompatibility, catalysis, molecular recognition, and surface chemistry. Also, the relation between molecular chirality of core or building block and the macroscopic chirality of dendritic objects is discussed.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031005
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  • 46
    Digitale Medien
    Digitale Medien
    Development of Tools for the Design of Selectin AntagonistsDedicated to Professor Hans Paulsen on the occasion of his 75th birthday (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1571-1578 
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    ISSN: 0947-6539
    Schlagwort(e): carbohydrates ; molecular modeling ; preorganization ; sialyl Lewisx ; selectins ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A molecular modeling tool for the rational design of E-selectin antagonists based on the lead structure sialyl Lewisx has been developed. The binding affinity to the receptor is considerably influenced by the entropy and consequently by the antagonist's ability to place its pharmacophores in an optimal spatial arrangement, i.e., by its preorganization for binding. The computational model assesses the preorganization of a potential selectin antagonist with the aid of Monte Carlo (jumping between wells)/stochastic dynamics [MC(JBW)/SD] simulations. The model has been validated by correlating preorganization and bioactivity of several selectin antagonists. The results suggest that only preorganized compounds are likely to bind to E-selectin.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031006
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  • 47
    Digitale Medien
    Digitale Medien
    Complex Formation of the Antiviral 9-[2-(Phosphonomethoxy)Ethyl]Adenine (PMEA) and of Its N 1, N 3, and N 7 Deaza Derivatives with Copper(II) in Aqueous SolutionAbbreviations and definitions: 2′-AMP2-, adenosine 2′-monophosphate; 3′-AMP2-, adenosine 3′-monophosphate; ATP4-, adenosine 5′-triphosphate; M2+, divalent metal ion; PA2- = PME2-, PMEA2-, and its twofold negatively charged deaza derivatives; R-PO2-3, simple phosphate monoester or phosphonate ligand with R representing a noncoordinating residue (see also Figure 1); TuMP2-, tubercidin 5′-monophosphate (=7-deaza-5′-AMP2-). Although the IUPAC nomenclature for the deazaadenine compounds is 3H-imidazo[4,5b]pyridine-7-amine (1-deazaadenine), imidazo[4,5c]pyridine-4-amine (3-deazaadenine), and pyrrolo[2,3d]pyrimidine-4-amine (7-deazaadenine), the trivial names and the numbering system for purines are retained in the present study to facilitate the comparison with the parent compound, PMEA2-, and other adenine derivatives. For example, 1-deaza-PMEA is thus named 9-[2-(phosphonomethoxy)ethyl]-1-deazaadenine. In mathematical expressions and tables, 1-, 3-, and 7-deaza-PMEA are written as 1d-, 3d-, and 7d-PMEA. In the text the expression „PMEAs“ encompasses PMEA as well as its three deaza derivatives. Species written without a charge either do not carry one or represent the species in general (i.e., independent of their protonation degree); which of the two possibilities applies is always clear from the context. (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1526-1536 
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    ISSN: 0947-6539
    Schlagwort(e): adenine ; isomerizations ; NMR spectroscopy ; nucleotides ; stability constants ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The stability constants of the 1:1 complexes formed between Cu2+ and the anions of the N 1, N 3, and N 7 deaza derivatives of 9-[2-(phosphonomethoxy)-ethyl]adenine (PA2-), Cu(H;PA)+ and Cu(PA), were determined by potentiometric pH titration in aqueous solution (25 °C; I = 0.1 M, NaNO3) and compared with previous results for 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA2-) and (phosphonomethoxy)ethane (PME2-). A microconstant scheme reveals that in Cu(H;PA)+ Cu2+ is coordinated to the nucleobase, H+ being at the phosphonate group, in about 90% of the Cu(H;PMEA)+ and Cu(H;1-deaza-PMEA)+ species, but only in about 37% and 12% of the corresponding complexes with H(3-deaza-PMEA)- and H(7-deaza-PMEA)-, respectively. Straight-line plots of log KCuCu(R-PO3) versus pKHH(R-PO3) for simple phosph(on)ate ligands show that all the Cu(PA) complexes, including those with PMEA2- and PME2-, are more stable than expected simply from the basicity of the -PO2- group; to some extent five-membered chelates (Cu(PA)cl/O) involving the ether oxygen of the -CH2-O-CH2-PO2-3 chain are formed, and in all complexes an additional nucleobase-metal-ion interaction occurs. Based on 1H NMR line-broadening measurements and structural considerations it is concluded that in Cu(3-deaza-PMEA) the interaction occurs with N7 whereas in Cu(7-deaza-PMEA), Cu(1-deaza-PMEA), and Cu(PMEA) it occurs with N3. The proof of a metal ion-N3 interaction is important (and also of relevance regarding DNA) because so far this interaction has received little attention. In all Cu(PA) systems three major isomeric species are in equilibrium; for example, 17(∓3)% of Cu(PMEA) exists as an isomer with a sole Cu2+-phosphonate coordination, 34(∓10)% as Cu(PMEA)cl/O, and in 49(∓10)% the Cu2+ is bound to the phosphonate group, the ether O, and N3. In contrast, 54(∓8)% of Cu(5′-AMP) occurs as an isomer with sole Cu2+-phosphate coordination and 46(∓8)% as a macrochelate involving N7 too.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970030922
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  • 48
    Digitale Medien
    Digitale Medien
    The Versatility of Lithium Reagents in Synthetic Organometallic Chemistry: Their differing reactions with [Cp*Mo(NO)(CH2SiMe3)2] (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1579-1587 
    Details
    ISSN: 0947-6539
    Schlagwort(e): alkylidene complexes ; lithium ; molybdenum ; nitric oxides ; tungsten ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: [Cp*Mo(NO)(CH2SiMe3)2] exhibits three principal types of reaction with the various lithium reagents investigated during this study, namely: regioselective deprotonation, reduction, and addition. Deprotonation of the reactant, achieved by treatment with lithium amide reagents, leads ultimately to the formation of the alkylidene „ate“ complex [Cp*Mo(NO)(CH2SiMe3)2(=CHSiMe3)]2-[Li2(thf)3] (1). While LiN(SiMe3)2 effects this conversion directly with no detectable intermediates, reaction with 1 equiv of LDA in THF for 15 min deprotonates the Cp* ligand to form the lithium salt of the „tucked-in“ ate complex [(η5,η1-C5Me4CH2)Mo(NO)(CH2SiMe3)2]-[Li(thf)3] (2) in 40% isolated yield. Complex 2 slowly converts to the thermodynamically more stable 1 when left as a THF or C6D6 solution at ambient temperature for 48 h. Reaction of the dialkyl starting material with either tBuLi or PhLi leads to the production of the alkylidene complex 1 in irreproducible yields (10-50% NMR; not isolable). A kinetic analysis of the reaction of [Cp*Mo(NO)(CH2SiMe3)2] with LiN(SiMe3)2 indicated that the reaction was first-order in both the lithium and molybdenum reagents, and the activation parameters of ΔH* = 7.3∓1.0 kcal mol-1 and ΔS* = - 34∓3 e.u. suggest an associative process. Treatment of the neutral dialkyl with 1 equiv of LiPPh2 in THF results in a one-electron reduction and production of {[Cp*Mo(NO)(CH2SiMe3)2[Li2(thf)3] (3). If left in solution, the 17e- dialkyl anion 3 is converted to the 18e- alkylidene anion 1 by the Ph2P-PPh2 coproduct, which effects the requisite hydrogen-atom abstraction. Finally, addition of a sterically undemanding alkyllithium reagent such as MeLi to the 16e- dialkyl reactant leads to the formation of the 18e- trialkyl anionic complex [[Cp*Mo(NO)(CH2SiMe3)2(=CHSiMe3)]2-[Li2(thf)3](Me)][Li(thf)3] (4). Warming of 4 in a C6D6 solution results in loss of methane and production of 1. In most cases, the chemistry exhibited by the Mo system is duplicated by the analogous W congener, [Cp*Mo(NO)(CH2SiMe3)2(=CHSiMe3)]2-[Li2(thf)3]. The solid-state molecular structures of complexes 1 and 4 have been established by single-crystal X-ray crystallographic analyses.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031007
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  • 49
    Digitale Medien
    Digitale Medien
    Cope Rearrangements versus Retro Diels-Alder ReactionsAzo Bridges from Azines, part 25; for part 24 see U. Brand, S. Hünig, K. Peters, F. Prokschy, H. G. von Schnering, Liebigs Ann. 1997, 785-789.Dedicated to Professor Dr. Dieter Seebach on the occasion of his 60th birthday (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1588-1599 
    Details
    ISSN: 0947-6539
    Schlagwort(e): azo compounds ; cycloadditions ; hydropyridazines ; pyrazolines ; rearrangements ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The two isomeric [4+2] cyclo-adducts from two different 1,3-dienes may result from direct cycloadditions as well as from Cope rearrangements (Scheme 1). This general question is tackled by employing two energetically different types of dienes, protonated pyrazolines (1H+, 2H+) or dihydropyridazines (3H+), prepared in situ from their trimers and alicyclic (4-6) or aliphatic (7-9) 1,3-dienes. Depending on structural features and conditions (amount of acid, reaction time), various ratios of the two isomeric [4+2] cycloadducts A and B are obtained; A and B are azo compounds 10, 14, 16, 20, 22, 24, 27, 32, 34, 36-39, 41, 42, pyrazolines endo-11, endo-13, endo-15, endo-endo-17, endo-18, endo-19, 21, 23, 25, 26, 28, and hydropyridazines 31, endo-33, endo-35, 40 and 43 (Schemes 3, 4). These results were backed by others from acid-catalyzed isomerizations, trapping experiments, and calculations of the equilibria (ΔΔH) between the isomers (by analogy with the corresponding olefins). A critical discussion reveals: a) Azo compounds 20, 22, 24, 27, 34, 38, and 42 must result from a [4++2] cycloaddition with inverse electron demand, whereas hydropyridazines endo-33, endo-35, 40, and 43 originate from a [4+2+] cycloaddition with normal electron demand. b) All isomerizations occur by a [3,3] sigmatropic rearrangement; [4+2] cycloreversion is energetically disfavored. c) A clear-cut distinction between the [4++2] or [4+2+] cycloaddition reaction routes to the energetically well-balanced systems 10→endo-11 and 12→endo-13 is not possible. d) The two cycloadditions may well favor a nonconcerted reaction through an allylic cationic intermediate which also governs the [3,3] rearrangements (Scheme 8).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031008
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  • 50
    Digitale Medien
    Digitale Medien
    The Nature of the Metal - Silicon Bond in [M(SiR3)H3(PPh3)3] (M = Ru, Os) And the Crystal Structure of [Os{Si(N-pyrrolyl)3}H3(PPh3)3] (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1608-1616 
    Details
    ISSN: 0947-6539
    Schlagwort(e): ab initio calculations ; hydrides ; osmium ; ruthenium ; silicon ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The compounds [M(SiR3)H3(PPh3)3] (1: M = Ru, R = 1 - NC4H4 = pyr; 2a-c: M = Os, R = pyr, Et, Ph) are prepared through reaction of either [RuH2(PPh3)4] or [OsH4(PPh3)3] with the appropriate silane HSiR3 (3a-c: R = pyr, Et, Ph). The X-ray structure analysis of compound 2 a and ab initio calculations on the model compounds [Os(SiR3)H3(PH3)3] (4a-c: R = H, NH2, pyr) reveal a trigonal distortion along the Os-Si axis from an idealised tetrahedral geometry for the central OsSiP3 heavy-atom skeleton. The structure can be described as two face-shared octahedra, one based on osmium (OsH3P3) and the other based on silicon (SiH3N3). Studies of the bonding situation in 2 a reveal that the N-pyrrolyl substituents have a marked shortening effect on the osmium-silicon distance (229.3(3) pm) and that each of the three hydride ligands participates in partial three-centre bonding involving osmium, silicon and hydrogen. 1H, 13C, 29Si and 31P NMR spectra were used to determine the solution structures of complexes 1 and 2 a.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031010
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  • 51
    Digitale Medien
    Digitale Medien
    A Pyrrole-Imidazole Polyamide Motif for Recognition of Eleven Base Pair Sequences in the Minor Groove of DNADedicated to Dieter Seebach on the occasion of his 60th birthday (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1600-1607 
    Details
    ISSN: 0947-6539
    Schlagwort(e): DNA recognition ; hydrogen bonds ; ligand design ; molecular recognition ; sequence-specificity ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A new upper limit of binding site size is defined for the 2:1 overlapped polyamide: DNA motif. Eight-ring polyamides composed of four-ring subunits containing pyrrole (Py) and imidazole (Im) amino acids linked by a central β-alanine (β) spacer („4-β-4 ligands“) were designed for recognition of eleven base pair sequences as antiparallel dimer (4-β-4)2.DNA complexes in the minor groove. The DNA binding properties of three polyamides, ImPyPyPy-β-PyPyPyPy-β-Dp, ImImPyPy-β-PyPyPyPy-β-Dp, and ImImImPy-β-PyPyPyPy-β-Dp, were analyzed by footprinting experiments on DNA fragments containing the respective match sites 5'-AGTAATTTACT-3', 5'-AGGTATTACCT-3', and 5'-AGGGATTCCCT-3' (Dp = dimethylaminopropylamide). Quantitative footprint titrations reveal that each polyamide binds its respective target site with subnanomolar affinity and 7-fold to over 30-fold specificity over double-base-pair mismatch sites. A 20-fold decrease in binding affinity is observed for placement of a side-by-side β-β pairing opposite G.C/C.G relative to placement opposite a A.T/T.A base pair. The use of side-by-side antiparallel β-alanine residues as an A.T/T.A-specific DNA binding element provides a new pairing rule for polyamide design. Expanding the DNA binding site size targeted by pyrrole-imidazole polyamides represents an important step in the development of cell-permeable synthetic ligands for the control of gene-specific regulation.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031009
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  • 52
    Digitale Medien
    Digitale Medien
    Toxicity and biodegradation of formaldehyde in anaerobic methanogenic culture (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 727-736 
    Details
    ISSN: 0006-3592
    Schlagwort(e): acetate ; anaerobic ; biodegradation ; formaldehyde ; methanogenic ; toxicity ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Formaldehyde is present in several industrial wastewaters including petrochemical wastes. In this study, the toxicity and degradability of formaldehyde in anaerobic systems were investigated. Formaldehyde showed severe toxicity to an acetate enrichment methanogenic culture. As low as 10 mg/L (0.33 mM) of formaldehyde in the reactor completely inhibited acetate utilization. Formaldehyde, however, was degraded while acetate utilization was inhibited. Degradation of formaldehyde (Initial concentration ≤30 mg/L) followed Monod model with a rate constant, k, of 0.35-0.46 d-1. At higher initial concentrations (≥60 mg/L), formaldehyde degradation was inhibited and partial degradation was possible. The initial formaldehyde to biomass ratio, S0/X0, was useful to predict the degradation potential of high formaldehyde concentrations in batch systems. When S0/X0 ≤ 0.1, formaldehyde was completely degraded with initial concentration of up to 95 mg/L; when S0/X0 ≥ 0.29, formaldehyde at higher than 60 mg/L was only partially degraded. The inhibition of formaldehyde degradation in batch systems could be avoided by repeated additions of low concentrations of formaldehyde (up to 30 mg/L). Chemostats (14-day retention time) showed degradation of 74 mg/L-d (1110 mg/L) of influent formaldehyde with a removal capacity of 164 mg/g VSS-day. A spike of 30 mg/L (final concentration in the chemostat) formaldehyde to the chemostat caused only a small increase in effluent acetate concentration for 3 days. But a spike of 60 mg/L (final concentration in the chemostat) formaldehyde to the chemostat resulted in a dramatic increase in acetate concentration in the effluent. The results also showed that the acetate enrichment culture was not acclimated to formaldehyde even after 226 days. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 727-736, 1997.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 53
    Digitale Medien
    Digitale Medien
    Linear scale ultrafiltration (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 737-746 
    Details
    ISSN: 0006-3592
    Schlagwort(e): ultrafiltration ; scale-up ; scale-down ; linear scale ; proteins ; membrane fouling ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Tangential flow filtration has traditionally been scaled up by maintaining constant the filtrate volume to membrane surface area ratio, membrane material and pore size, channel height, flow path geometry and retentate and filtrate pressures. Channel width and the number of channels have been increased to provide increased membrane area. Several other parameters, however, have not been maintained constant. A new comprehensive methodology for implementation of linear scale up and scale down of tangential flow filtration processes has been developed. Predictable scale up can only be achieved by maintaining fluid dynamic parameters which are independent of scale. Fluid dynamics are controlled by operating parameters (feed flow rate, retentate pressure, fed batch ratio and temperature), geometry (channel length, height, turbulence promoter and entrance/exit design), materials (membrane, turbulence promoter, and encapsulant compression), and system geometry (flow distribution). Cassette manufacturing procedures and tolerances also play a significant role in achieving scale independent performance. Extensive development work in the aforementioned areas has resulted in the successful implementation of linear scale up of ultrafiltration processes for recovery of human recombinant DNA derived pharmaceuticals. A 400-fold linear scale up has been achieved without intermediate pilot scale tests. Scale independent performance has a direct impact on process yield, protein quality and product economics and is therefore particularly important in the biotechnology industry. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 737-746, 1997.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 54
    Digitale Medien
    Digitale Medien
    Thermodynamic analysis of solvent effect on substrate specificity of lyophilized enzymes suspended in organic media (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 340-344 
    Details
    ISSN: 0006-3592
    Schlagwort(e): subtilisin ; chymotrypsin ; substrate specificity ; organic solvents ; lyophilized enzymes ; stereoselectivity ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A simple methodology has been successfully employed to explain the solvent dependence of the substrate specificity of enzymes in organic media. This methodology, which does not require the knowledge of the enzyme structure and is thus applicable to lyophilized and other noncrystalline enzyme preparations, predicts that the kcat/KM ratio for two substrates should be proportional to their Raoult's law activity coefficients. This approach has been validated for two enzymes, subtilisin Carlsberg and α-chymotrypsin, catalyzing the propanolysis of unnatural (in addition to natural) ester substrates in a variety of anhydrous solvents. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 340-344, 1997.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 55
    Digitale Medien
    Digitale Medien
    Influence of Primatone RL supplementation on sialylation of recombinant human interferon-γ produced by Chinese hamster ovary cell culture using serum-free media (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 353-360 
    Details
    ISSN: 0006-3592
    Schlagwort(e): Primatone RL ; sialylation ; interferon-γ ; serum substitutes ; cell ; CHO cell culture ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Although serum-free media have been widely used in mammalian cell culture for therapeutic protein production, the effects of serum-substitutes on product quality have not been extensively examined. This study observed an adverse effect of Primatone RL, an animal tissue hydrolysate commonly used as a serum-substitute to promote cell growth, on sialylation of interferon-γ (IFN-γ) derived from Chinese hamster ovary (CHO) cell culture in both batch and fed-batch modes. In batch cultures, decreased sialylation was observed at each of the glycosylation sites (i.e., Asn25 and Asn97) of IFN-γ with the use of elevated concentrations of the peptone. Although poorest sialylation was obtained with the use of a growth-inhibiting concentration of Primatone RL, diminished sialylation was observed at the optimal peptone concentration for cell growth and product yield. Since incubation of the product in Primatone RL-supplemented acellular medium did not result in decreased sialylation, the negative effect of Primatone RL could not be attributed to extracellular desialylation of IFN-γ by components of the peptone. In the fed-batch mode, a culture utilizing a serum-free feeding medium supplemented with Primatone RL demonstrated poorer sialylation than a similar culture not fed the peptone. The results of both the batch and fed-batch experiments indicate that the adverse effect of the peptone was not due solely to ammonia accumulation. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 353-360, 1997.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 56
    Digitale Medien
    Digitale Medien
    bcl-2 expression in Spodoptera Frugiperda Sf-9 and Trichoplusia Ni BTI-Tn-5B1-4 insect cells: Effect on recombinant protein expression and cell viability (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 380-390 
    Details
    ISSN: 0006-3592
    Schlagwort(e): insect cells ; baculovirus ; bcl-2 ; recombinant proteins ; cell viability ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The effect of bcl-2 expression on cell viability and recombinant protein synthesis was investigated in the Spodoptera frugiperda Sf-9 and Trichoplusia ni BTI-Tn-5B1-4 (High Five™) insect cell lines. It was found that coinfection with a baculovirus expressing bcl-2 [Autographa californica nuclear polyhedrosis virus (AcNPV)-bcl2] extended the life span of High Five™ cells but not Sf-9 cells when compared to infection with recombinant baculoviruses expressing either human tissue plasminogen activator (AcNPV-tPA) or Escherichia coli β-galactosidase (AcNPV-βgal). Similar results were obtained in coinfection experiments; i.e., AcNPV-bcl2 coinfection increased the life span of High Five™ cells over that of cells infected with either AcNPV-tPA or AcNPV-βgal alone, but they did not affect the life span of coinfected Sf-9 cells. Coinfection of Sf-9 cells with AcNPV-bcl2 and AcNPV-βgal resulted in a decrease in the maximum β-gal expression levels of over 90% when compared to infection with AcNPV-βgal alone. A similar trend was found in the β-gal mRNA levels. Coinfection also resulted in a reduced β-gal expression level in High Five™ cells, but the reduction was consistent with what would be expected when two recombinant viruses compete for use of the cellular machinery. In contrast to the inhibitory effect of AcNPV-bcl2 coinfection on βgal expression, t-PA expression levels were either not affected (Sf-9 cells) or were increased 50% (High Five™ cells) over those obtained by infection with AcNPV-tPA alone. These results support the hypotheses that bcl-2 can inhibit transcription of genes under polyhedrin promoter control and that β-gal expression levels, but not t-PA expression levels, are controlled at the transcriptional level. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 380-390, 1997.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 57
    Digitale Medien
    Digitale Medien
    Simple dissolution-reaction model for enzymatic conversion of suspension of solid substrate (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 433-440 
    Details
    ISSN: 0006-3592
    Schlagwort(e): simple dissolution-reaction model ; enzymatic conversion ; solid substrate suspension ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Although reactions in substrate suspension are employed in industry for several bioconversion processes, there appears to be no quantitative model available in the literature to rationalize the optimization of these processes. We present a simple model that incorporates the kinetics of substrate dissolution and a simultaneous enzymatic reaction. The model was tested in the α-chymotrypsin-catalyzed hydrolysis of an aqueous suspension of dimethyl benzylmethylmalonate to a homogeneous solution of enantiomerically pure monoester. This reaction occurs in the bulk phase, so catalysis by enzyme absorbed at the solid-liquid interface plays no role. The value of the parameters in the model (i.e., the mass transfer coefficient of substrate dissolution (kL), the substrate solubility, and the rate constant for the enzymatic reaction) were determined in separate experiments. Using these parameter values, the model gave a good quantitative prediction of the rate of the overall dissolution-reaction process. When the particle size distribution is known, kL may also be calculated instead. The model seems to be applicable also for other poorly soluble substrates, other enzymes, and other solvents. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 433-440, 1997.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 58
    Digitale Medien
    Digitale Medien
    Enzymatic condensation of cholecystokinin CCK-8 (4-6) and CCK-8 (7-8) peptide fragments in organic media (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 456-463 
    Details
    ISSN: 0006-3592
    Schlagwort(e): enzymatic fragment condensation ; α-chymotrypsin ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The kinetically controlled condensation reaction of Z-Gly-Trp-Met-OR1 (R1: Et, Al, Cam) and H-Asp-(OR2)-Phe-NH2 (R2: H, But) catalyzed by α-chymotrypsin deposited onto polyamide in organic media was studied. The effect of the drying process of the enzyme-support preparation, substrate concentrations, reaction medium, acyl donor, and nucleophile structure on both enzymatic activity and pentapeptide yield was investigated. The immobilized preparation directly equilibrated at aw = 0.113, gave higher enzymatic activities than dried with vacuum first, and then equilibrated at aw = 0.113. The addition of triethylamine to the reaction medium increased dramatically the enzymatic activity. However, the pentapeptide yield was affected neither by the drying procedure nor by the addition of triethylamine. The donor ester Z-Gly-Trp-Met-OAl gave initial reaction rates 2.6 times higher than the conventional ethyl ester derivative but rendered similar yields. The best results were obtained using Z-Gly-Trp-Met-OCam as acyl-donor ester; 80% yield and initial reaction rates 4 times higher than the ethyl ester derivative. In all cases, acetonitrile containing Tris-HCl 50 mM pH 9 buffer (0.5% v/v) and triethylamine (0.5% v/v) was found to be the best reaction system. Under these conditions, it was possible to use the nucleophile H-Asp-Phe-NH2 with β-unprotected aspartic acid residue. In this case, 50% yield was obtained, but economic considerations could lead to select it as nucleophile. Finally, the fragment condensation reaction was carried out at gram scale, obtaining a 39% yield which included the reaction, removal of protecting groups and purification steps. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 456-463, 1997.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 59
    Digitale Medien
    Digitale Medien
    Production of recombinant proteins in transgenic plants: Practical considerations (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 473-484 
    Details
    ISSN: 0006-3592
    Schlagwort(e): transgenic plants ; recombinant protein ; gene expression ; downstream processing ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: This review is based on our recent experience in producing the first commercial recombinant proteins in transgenic plants. We bring forward the issues that have to be considered in the process of selecting and developing a winning transgenic plant production system. From the production point of view, transcription, posttranscription, translation, and posttranslation are important events that can affect the quality and quantity of the final product. Understanding the rules of gene expression is required to develop sound strategies for optimization of recombinant protein production in plants. The level of recombinant protein accumulation is critical, but other factors such as crop selection, handling and processing of transgenic plant material, and downstream processing are equally important when considering commercial production. In some instances, the cost of downstream processing alone may determine the economic viability of a particular plant system. Some of the potential advantages of a plant production system such as the high levels of accumulation of recombinant proteins, glycosylation, compartmentalization within the cell, and natural storage stability in certain organs are incentives for aggressively pursuing recombinant protein production in plants. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 473-484, 1997.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 60
    Digitale Medien
    Digitale Medien
    Ammonium toxicity in different cell lines (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 530-537 
    Details
    ISSN: 0006-3592
    Schlagwort(e): ammonium ; cell culture ; cell cycle ; cell death ; cell growth ; Jurkat cells, GH4 cells ; LLC-PK1 cells ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The toxic effect of ammonium upon a variety of cell lines of lymphoid (Jurkat), pituitary (GH4), and renal (LLC-PK1) origin was studied. Millimolar concentrations of the ion mildly affected the growth of GH4 cells and prevented the growth of LLC-PK1 cells. The ion did not lead to the death of LLC-PK1 cells but it produced morphologic changes in these cells. The effects of ammonium upon Jurkat cells were different because cells died after accumulating at S phase. Cell death was due to apoptosis and might be related to ammonium-induced calcium mobilization from intracellular stores. These results indicate that the toxic effects caused by ammonium accumulation are different depending upon the cell type. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 530-537, 1997.
    Zusätzliches Material: 8 Ill.
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  • 61
    Digitale Medien
    Digitale Medien
    The continuous isolation of trypsin by affinity adsorbent recycling (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 538-545 
    Details
    ISSN: 0006-3592
    Schlagwort(e): affinity ; separation ; purification ; continuous ; trypsin ; protein ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A method for the continuous affinity separation of proteins is described in which the adsorbent, in the form of a polymer belt, is recycled through feedstock and eluent liquid flows. As the belt is nonporous, contact between the solute and the ligand is not diffusion-dependent. Consequently, rapid cycle rates are possible. Soybean trypsin inhibitor immobilized on nylon was used as an affinity ligand for the isolation of trypsin. During a 30-h continuous run, trypsin was isolated from a crude preparation of bovine pancreas with a recovery of 30% to 40%. Approximately 18 mg of trypsin was obtained from 500 mg of protein using a total of approximately 10 μg of ligand. Electrophoretic analysis of the eluent showed that chymotrypsin, which also binds to SBTI, was the only major contaminant of the product. It was demonstrated that the highest rates of protein purification were obtained using solid/liquid contact times well below that required to achieve saturation of the affinity adsorbent. Slower adsorbent recycle rates, which achieved higher protein binding per unit area of belt, resulted in lower protein purification per unit time. The rate of purification was also dependent on the concentration of target protein in the adsorption chamber at steady state. As high concentrations increased losses from the chamber outflow, this resulted in a compromise between throughput and recovery during the adsorption phase. Under the conditions investigated, recoveries of over 60% were obtained, and a maximum throughput of approximately 2.5 mg trypsin per hour was achieved. Preliminary studies have shown that this can be improved by compartmentalizing the adsorption chamber, which can reduce losses from the adsorption chamber to less than 5%. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 538-545, 1997.
    Zusätzliches Material: 7 Ill.
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  • 62
    Digitale Medien
    Digitale Medien
    Immobilization of invertase on sepharose-linked enzyme glycosyl recognizing polyclonal antibodies (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 605-609 
    Details
    ISSN: 0006-3592
    Schlagwort(e): affinity immobilization ; glycoenzymes ; thermal stability ; non-inhibitory antienzyme antibodies ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Polyclonal antibodies directed against the yeast invertase glycosyls were raised by immunizing rabbits with neoglycoprotein-I and neoglycoprotein-II. The neoglycoproteins were prepared by separately coupling the N-linked large and small molecular weight yeast invertase oligosaccharides respectively to bovine serum albumin with the help of glutaraldehyde. Antibodies specifically recognizing the invertase oligosaccharides were purified from the sera of rabbits immunized with either neoglycoprotein using an affinity column of sepharose 4B-linked yeast invertase. Specific immunoaffinity supports for the immobilization of invertase were constructed by coupling the affinity-purified antineoglycoprotein-I or antineoglycoprotein-II antibodies to cyanogen bromide activated sepharose-4B. Both the affinity adsorbants were effective in binding and improving the thermal stability of invertase. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 605-609, 1997.
    Zusätzliches Material: 5 Ill.
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  • 63
    Digitale Medien
    Digitale Medien
    Reduction of albumin adsorption onto silicon surfaces by Tween 20 (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 618-625 
    Details
    ISSN: 0006-3592
    Schlagwort(e): albumin ; silicon ; hydrophobicity ; adsorption ; Tween 20 ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The ability of Tween 20 to reduce the adsorption of albumin on silicon surfaces of different hydrophobicity was investigated by ellipsometry. As expected, protein adsorption was found to depend on the degree of hydrophobicity of the surfaces and on the concentration of the surfactant. A reduction of 90% in albumin adsorption on hydrophobic methylated surfaces by 0.05% Tween 20 was achieved, whereas a reduction of only 15% on hydrophilic surfaces was observed. Experiments of time-dependent protein adsorption in both pure protein and protein-surfactant mixtures were conducted to ascertain the stability of physically adsorbed Tween 20 films on intermediate silicon surfaces. It was found that the adsorbed Tween 20 film was robust and there was no evidence of exchange of the Tween molecules with albumin for up to 240 min exposure. Adsorption minima were confirmed to correlate with minima in contact angle and critical micelle concentration (CMC). © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 618-625, 1997.
    Zusätzliches Material: 7 Ill.
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  • 64
    Digitale Medien
    Digitale Medien
    Optimizing seeding and culture methods to engineer smooth muscle tissue on biodegradable polymer matrices (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 57 (1998), S. 46-54 
    Details
    ISSN: 0006-3592
    Schlagwort(e): smooth muscle ; polyglycolic acid ; biodegradable ; tissue engineering ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The engineering of functional smooth muscle (SM) tissue is critical if one hopes to successfully replace the large number of tissues containing an SM component with engineered equivalents. This study reports on the effects of SM cell (SMC) seeding and culture conditions on the cellularity and composition of SM tissues engineered using biodegradable matrices (5 × 5 mm, 2-mm thick) of polyglycolic acid (PGA) fibers. Cells were seeded by injecting a cell suspension into polymer matrices in tissue culture dishes (static seeding), by stirring polymer matrices and a cell suspension in spinner flasks (stirred seeding), or by agitating polymer matrices and a cell suspension in tubes with an orbital shaker (agitated seeding). The density of SMCs adherent to these matrices was a function of cell concentration in the seeding solution, but under all conditions a larger number (approximately 1 order of magnitude) and more uniform distribution of SMCs adherent to the matrices were obtained with dynamic versus static seeding methods. The dynamic seeding methods, as compared to the static method, also ultimately resulted in new tissues that had a higher cellularity, more uniform cell distribution, and greater elastin deposition. The effects of culture conditions were next studied by culturing cell-polymer constructs in a stirred bioreactor versus static culture conditions. The stirred culture of SMC-seeded polymer matrices resulted in tissues with a cell density of 6.4 ± 0.8 × 108 cells/cm3 after 5 weeks, compared to 2.0 ± 1.1 × 108 cells/cm3 with static culture. The elastin and collagen synthesis rates and deposition within the engineered tissues were also increased by culture in the bioreactors. The elastin content after 5-week culture in the stirred bioreactor was 24 ± 3%, and both the elastin content and the cellularity of these tissues are comparable to those of native SM tissue. New tissues were also created in vivo when dynamically seeded polymer matrices were implanted in rats for various times. In summary, the system defined by these studies shows promise for engineering a tissue comparable in many respects to native SM. This engineered tissue may find clinical applications and provide a tool to study molecular mechanisms in vascular development. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 57: 46-54, 1998.
    Zusätzliches Material: 8 Ill.
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  • 65
    Digitale Medien
    Digitale Medien
    Thermophilic sulphate and sulphite reduction in lab-scale gas-lift reactors using H2 and CO2 as energy and carbon source (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 807-814 
    Details
    ISSN: 0006-3592
    Schlagwort(e): sulphate reduction ; sulphite reduction ; biofilm ; immobilization ; gas-lift reactor ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Feasibility of thermophilic (55°C) sulphate and sulphite reduction with H2 and CO2 gas-mixtures was studied in gas-lift reactors, which contained pumice particles as carrier material. Particular attention was paid to biomass retention and the competition between hydrogenotrophic sulphate-reducers and other hydrogenotrophic thermophiles. A model medium with defined mineral nutrients was used.The results of the experiments clearly demonstrate that sulphate conversion rates up to 7.5 g SO42-/L per day can be achieved. With sulphite, a reduction rate of 3.7 g S/L per day was obtained, which equals a sulphate conversion rate of 11.1 g SO42-/L per day. Under the applied conditions, a strong competition for hydrogen between hydrogenotrophic sulphate-reducers, tentatively designated as Desulfotomaculum sp., and hydrogenotrophic methanogens was observed. The outcome of the competition could not be predicted. Growth of the mixed culture was totally inhibited at an H2S concentration of 250 mg/L. Poor attachment of sulphate-reducing bacteria was observed in all experiments. The biomass concentration did not exceed 1.2 g/L, despite the presence of 50 g/L of pumice. The reason for this phenomenon remains to be understood. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 807-814, 1997.
    Zusätzliches Material: 3 Ill.
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  • 66
    Digitale Medien
    Digitale Medien
    Effect of substrate concentration and nitrate inhibition on product release and heavy metal removal by a Citrobacter sp. (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 821-830 
    Details
    ISSN: 0006-3592
    Schlagwort(e): Citrobacter ; actinides ; nitrate ; biomineralization ; biocatalysis ; phosphatase ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A Citrobacter sp. accumulates heavy metals as cell-bound metal phosphates, utilizing phosphate released by the enzymatic cleavage of a phosphomonoester substrate. The effect of increased substrate (glycerol 2-phosphate, G2P) concentration on phosphate release and heavy metal accumulation was evaluated using a stirred tank reactor (STR) and a plug flow reactor (PFR). A significant improvement in metal removal was achieved with increased substrate concentration using immobilized Citrobacter cells in the PFR, which was not observed using free cells in the STR. Nitrate is an inhibitor of the Citrobacter phosphatase. This inhibition was concentration dependent and reversible. The rate of product release was restored by increasing the concentration of substrate (G2P). The ratio of rates of phosphate release under two different conditions (different nitrate and G2P concentrations) can be described by a equation developed from Michaelis-Menten kinetics. The concentration of substrate required for restoration of maximum velocity, Vmax, in a batch and continuous-flow system can be predicted by substitution and calculation; this was confirmed by an experiment in model systems using cell suspensions and polyacrylamide gel immobilized cells in a flow-though column. For use in industrial situations it may be uneconomical or infeasible to supply additional substrate. Bioreactor activity was also restored by increasing the flow residence time, in accordance with a Michaelis-Menten-based model to describe removal of lanthanum from nitrate-supplemented flow in a PFR. © 1997 John Wiley & Sons, Inc. Biotechnol Biotechnol Bioeng 55:821-830, 1997.
    Zusätzliches Material: 7 Ill.
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  • 67
    Digitale Medien
    Digitale Medien
    Transient studies of nutrient uptake, growth, and indole alkaloid accumulation in heterotrophic cultures of hairy roots of Catharanthus roseus (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 527-534 
    Details
    ISSN: 0006-3592
    Schlagwort(e): Catharanthus roseus ; hairy roots ; indole alkaloids ; organic acids ; nutrients ; growth association ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The kinetics of growth, the uptake of macronutrients, and the accumulation of indole alkaloids were investigated in long-term, heterotrophically cultured transgenic (“hairy”) roots of Catharanthus roseus.Tabersonine, ajmalicine, and serpentine were monitored over a 70-day period. The doubling time [dry-weight (DW) basis] of C. roseus hairy roots in B5/2 nutrients supplemented with 3% sucrose was 3.6 days. NH4+, NO3,- and Pi were depleted sequentially from culture medium by hairy roots, while sugars remained undepleted. The growth-limiting nutrient was inorganic nitrogen, NH4+ and NO3-, with exponential-phase overall biomass yields of 34.1 and 5.0 g DW/g nutrient, respectively. Extracellular pH decreased to 4.8 in early exponential phase of culture growth from the initially adjusted value of 5.7, increased subsequently to a maximum of 7.7 in late exponential phase of growth coincident with the maximum of fresh weight (FW)/DW ratio, before decreasing to 5.5-5.0. The organic acids, pyruvate, formate, lactate, and succinate were excreted by hairy roots starting in late phase of exponential growth, possibly resulting in the late-culture pH decrease. Tabersonine accumulation was distinctly growth associated with maximum specific and total yields of 1.15 mg/g DW and 5.6 mg/L, respectively, in late-exponential phase of growth. Serpentine accumulation was non growth associated with increasing specific and total levels in stationary growth phase: 1.3 mg/g DW and 10.5 mg/L, respectively. The accumulation of ajmalicine also appeared growth associated. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 527-534, 1997.
    Zusätzliches Material: 5 Ill.
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  • 68
    Digitale Medien
    Digitale Medien
    Antiserum inhibition of propagating viruses (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 542-546 
    Details
    ISSN: 0006-3592
    Schlagwort(e): virus ; antibody ; imaging ; real-time ; phage T7 ; diffusion ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The design and implementation of controlled environments to continuously culture and evolve viruses provides a means to track how their populations respond to natural and designed anti-viral agents. We have previously demonstrated how the growth of viruses in spreading plaques enables detection and characterization of their evolutionary dynamics. Using plaques of phage T7 growing on E. coli as a model system, we observe here that velocities of propagation can be readily controlled by the level of anti-viral antiserum incorporated into the propagation medium. Further, we develop a simple analytic expression for the radial velocity of propagation in terms of the microscopic rates of viral amplification, Fickian diffusion of the virions and their neutralization by antiserum. Our analysis captures the essential dependence of propagation velocity on antiserum concentration. This study provides an ex vivo foundation for exploring how medically relevant viruses escape suppression by the immune system. © 1997 John Wiley & Son, Inc. Biotechnol Bioeng 55: 542-546, 1997.
    Zusätzliches Material: 4 Ill.
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  • 69
    Digitale Medien
    Digitale Medien
    Model of energy uncoupling for substrate-sufficient culture (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 571-576 
    Details
    ISSN: 0006-3592
    Schlagwort(e): substrate-sufficient culture ; anabolism ; catabolism ; energy uncoupling ; growth yield ; residual substrate concentration ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The growth yields (Yobs) are greater under substrate-limited conditions than those under substrate-sufficient conditions in continuous cultures. This indicates that the excess substrate should cause uncoupling between anabolism and catabolism, which leads to energy spilling. Although the uncoupling between anabolism and catabolism has already been recognized in the microbiology literature, how to quantitatively describe such uncoupling remains unclear. Based on a balance on substrate reaction, a growth yield model was developed in relation to residual substrate concentration for substrate-sufficient continuous cultures. On the basis of that yield model, the concept of an uncoupling coefficient between anabolism and catabolism is defined in this work. A model describing the effect of the residual substrate concentration on the uncoupling coefficient of anabolism to catabolism is proposed. This model agrees very well with literature data. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 571-576, 1997.
    Zusätzliches Material: 4 Ill.
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  • 70
    Digitale Medien
    Digitale Medien
    Cumulative sedimentation analysis of Escherichia coli debris size (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 556-564 
    Details
    ISSN: 0006-3592
    Schlagwort(e): cumulative sedimentation analysis ; cell debris size ; Escherichia coli ; homogenization ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A new method to measure Escherichia coli cell debris size after homogenization is presented. It is based on cumulative sedimentation analysis under centrifugal force, coupled with Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis (SDS-PAGE) analysis of sedimented proteins. The effects that fermentation and homogenization conditions have on the resulting debris distributions were investigated using this method. Median debris size decreased significantly from approximately 0.5 μm to 0.3 μm as the number of homogenization passes increased from 2 to 10. Under identical homogenization conditions, uninduced host cells in stationary phase had a larger debris size than exponential cells after 5 homogenizer passes. This difference was not evident after 2 or 10 passes, possibly because of confounding intact cells and the existence of a minimum debris size for the conditions investigated. Recombinant cells containing protein inclusion bodies had the smallest debris size following homogenization. The method was also used to measure the size distribution of inclusion bodies. This result compared extremely well with an independent determination using centrifugal disc photosedimentation (CDS), thus validating the method. This is the first method that provides accurate size distributions of E. coli debris without the need for sample pretreatment, theoretical approximations (e.g. extinction coefficients), or the separation of debris and inclusion bodies prior to analysis. © 1997 John Wiley & Sons, Inc. Biotechnol Bioang 55: 556-564, 1997.
    Zusätzliches Material: 7 Ill.
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  • 71
    Digitale Medien
    Digitale Medien
    Effect of hypoosmotic stress on hybridoma cell growth and antibody production (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 565-570 
    Details
    ISSN: 0006-3592
    Schlagwort(e): hybridoma ; hypoosmotic stress ; specific antibody productivity ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: To investigate the response of hybridoma cells to hypoosmotic stress, S3H5/γ2bA2 and DB9G8 hybridomas were cultivated in the hypoosmolar medium [Dulbecco's modified Eagle's medium (DMEM) supplemented with 10% serum] resulting from sodium chloride subtraction. Both hybridomas showed similar responses to hypoosmotic stress in regard to cell growth and antibody production. The cell growth and antibody production at 276 mOsm/kg were comparable to those at 329 mOsm/kg (standard DMEM). Both cells grew well at 219 mOsm/kg, though their growth and antibody production were slightly decreased. When the osmolality was further decreased to 168 mOsm/kg, the cell growth did not occur. When subjected to hyperosmotic stress, both cells displayed significantly enhanced specific antibody productivity (qAb). However, the cells subjected to hypoosmotic stress did not display enhanced qAb. Taken together, both hyperosmotic and hypoosmotic stresses depressed the growth of S3H5/γ2bA2 and DB9G8 hybridomas. However, their response to hypoosmotic stress in regard to qAb was different from that to hyperosmotic stress. © 1997 John Wiley & Sons, Inc. Biotechnol Biong 55: 565-570, 1997.
    Zusätzliches Material: 5 Ill.
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  • 72
    Digitale Medien
    Digitale Medien
    Production of recombinant bacterial endoglucanase as a co-product with ethanol during fermentation using derivatives of Escherichia coli KO11 (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 547-555 
    Details
    ISSN: 0006-3592
    Schlagwort(e): ethanol ; cellulose ; hemicellulose ; endoglucanase ; cellulase ; lignocellulose ; biomass ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: This study demonstrates a new approach to reduce the amount of fungal cellulase required for the conversion of cellulose into ethanol. Escherichia coli KO11, a biocatalyst developed for the fermentation of hemicellulose syrups, was used to produce recombinant endoglucanase as a co-product with ethanol. Seven different bacterial genes were expressed from plasmids in KO11. All produced cell-associated endoglucanase activity. KO11(pLOI1620) containing Erwinia chrysanthemi celZ (EGZ) produced the highest activity, 3,200 IU endoglucanase/L fermentation broth (assayed at pH 5.2 and 35°C). Recombinant EGZ was solubilized from harvested cells by treatment with dilute sodium dodecyl sulfate (12.5 mg/ml, 10 min, 50°C) and tested in fermentation experiments with commercial fungal cellulase (5 filter paper units/g cellulose) and purified cellulose (100 g/L). Using Klebsiella oxytoca P2 as the biocatalyst, fermentations supplemented with EGZ as a detergent-lysate of KO11(pLOI1620) produced 14%-24% more ethanol than control fermentations supplemented with a detergent-lysate of KO11(pUC18). These results demonstrate that recombinant bacterial endoglucanase can function with fungal cellulase to increase ethanol yield during the simultaneous saccharification and fermentation of cellulose. © 1997 Wiley & Sons, Inc. Biotechnol Bioeng 55: 547-555, 1997.
    Zusätzliches Material: 4 Ill.
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  • 73
    Digitale Medien
    Digitale Medien
    Engineering mRNA stability in E. coli by the addition of synthetic hairpins using a 5′ cassette system (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 577-580 
    Details
    ISSN: 0006-3592
    Schlagwort(e): mRNA stability ; hairpins ; gene expression control ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: An expression system has been developed for the introduction of DNA cassettes into the region between the transcription and translation start sites of a gene of interest. This cassette system was used to engineer mRNA stability through the introduction of hairpins at the 5′ end. A synthetic DNA cassette was designed so that the resulting mRNA hairpin would be positioned one nucleotide from the 5′ mRNA end. The hairpin-containing mRNA exhibited a half-life 3 times that of the mRNA with no hairpin, resulting in increases in both mRNA and protein levels. These results indicate that it is possible to engineer mRNA stability as an additional means of controlling gene expression. © 1997 John Wiley & Sons Inc. Biotechnol Bioeng 55: 557-580, 1997
    Zusätzliches Material: 3 Ill.
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  • 74
    Digitale Medien
    Digitale Medien
    Application of membrane-based preferential transport to whole broth processing (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 581-591 
    Details
    ISSN: 0006-3592
    Schlagwort(e): adsorptive membranes ; oscillatory flow ; integrated processes ; in situ product recovery ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Preferential transport in adsorptive membranes can be used to selectively remove biochemicals directly from fermentation broths. During preferential transport, an adsorbing solute is selectively transported across the membrane while nonadsorbing solutes and cells are retained by the membrane. This technique was used to separate lysozyme directly from a feed containing lysozyme, myoglobin, and yeast cells. We found that because the oscillatory flows used in preferential transport involve strokes that are close to symmetric, they are very efficient in alleviating cake formation due to cell deposition on the membrane surface. Theoretical results suggest that, by optimizing process variables, preferential transport can lead to a continuous concentrated stream of the adsorbing protein. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 54: 581-591, 1997.
    Zusätzliches Material: 11 Ill.
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  • 75
    Digitale Medien
    Digitale Medien
    In vivo analysis of metabolic dynamics in Saccharomyces cerevisiae: II. Mathematical model (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 592-608 
    Details
    ISSN: 0006-3592
    Schlagwort(e): Saccharomyces cerevisiae ; metabolic modeling ; sensitivity analysis ; glycolysis ; compartmentation ; transient response ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A mathematical model of glycolysis in Saccharomyces cerevisiae is presented. The model is based on rate equations for the individual reactions and aims to predict changes in the levels of intra- and extracellular metabolites after a glucose pulse, as described in part I of this study. Kinetic analysis focuses on a time scale of seconds, thereby neglecting biosynthesis of new enzymes. The model structure and experimental observations are related to the aerobic growth of the yeast. The model is based on material balance equations of the key metabolites in the extracellular environment, the cytoplasm and the mitochondria, and includes mechanistically based, experimentally matched rate equations for the individual enzymes. The model includes removal of metabolites from glycolysis and TCC for biosynthesis, and also compartmentation and translocation of adenine nucleotides. The model was verified by in vivo diagnosis of intracellular enzymes, which includes the decomposition of the network of reactions to reduce the number of parameters to be estimated simultaneously. Additionally, sensitivity analysis guarantees that only those parameters are estimated that contribute to systems trajectory with reasonable sensitivity. The model predictions and experimental observations agree reasonably well for most of the metabolites, except for pyruvate and adenine nucleotides. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 592-608, 1997.
    Zusätzliches Material: 11 Ill.
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  • 76
    Digitale Medien
    Digitale Medien
    A novel membrane reactor design for controlled studies of interacting populations (simulation of the interaction between microorganism and plant suspension cultures) (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 609-615 
    Details
    ISSN: 0006-3592
    Schlagwort(e): interacting populations ; membrane reactor ; induced metabolic changes ; elicitation ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The design of a reactor in which two interacting cell populations (microorganisms and plants) could grow under controlled conditions was considered. In this reactor, the cell populations are separated by a membrane which permits semi-in vivo study of induced interaction-specific changes in metabolism. In this paper, the interaction of suspension culture of Nicotiana tabacum (tobacco) and the Oomycete, Phytophthora nicotiana was simulated. The results of the computer simulation show the induced metabolic changes as a consequence of the biological interaction. The paper introduces a novel approach in the strategy for the study of interacting population in suspension cultures. This type of system has potential applications in studies of the regulation of secondary metabolism and for the production of high values pharmaceuticals. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 609-615, 1997.
    Zusätzliches Material: 3 Ill.
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  • 77
    Digitale Medien
    Digitale Medien
    Application of fluid mechanic and kinetic models to characterize mammalian cell detachment in a radial-flow chamber (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 616-629 
    Details
    ISSN: 0006-3592
    Schlagwort(e): cell adhesion ; radial-flow chamber ; hydrodynamic shear ; detachment kinetics ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The strength of adhesion and dynamics of detachment of murine 3T3 fibroblasts from self-assembled monolayers were measured in a radial-flow chamber (RFC) by applying models for fluid mechanics, adhesion strength probability distributions, and detachment kinetics. Four models for predicting fluid mechanics in a RFC were compared to evaluate the accuracy of each model and the significance of inlet effects. Analysis of these models indicated an outer region at large radial positions consistent with creeping flow, an intermediate region influenced by inertial dampening, and an inner region dominated by entrance effects from the axially-oriented inlet. In accompanying experiments patterns of the fraction of cells resisting detachment were constructed for individual surfaces as a function of the applied shear stress and evaluated by comparison with integrals of both a normal and a log-normal distribution function. The two functions were equally appropriate, yielding similar estimates of the mean strength of adhesion. Further, varying the Reynolds number in the inlet, Red, between 630 and 1480 (corresponding to volumetric flow rates between 0.9 and 2.1 mL/s) did not affect the mean strength of adhesion. For these same experiments, analysis of the dynamics of detachment revealed three temporal phases: 1) rapid detachment of cells at the onset of flow, consistent with a first-order homogeneous kinetic model; 2) time-dependent rate of detachment during the first 30 sec. of exposure to hydrodynamic shear, consistent with the first-order heterogeneous kinetic model proposed by Dickinson and Cooper (1995); and 3) negligible detachment, indicative of pseudo-steady state after 60 sec. of flow. Our results provide rigorous guidelines for the measurement of adhesive interactions between mammalian cells and prospective biomaterial surfaces using a RFC. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 616-629, 1997.
    Zusätzliches Material: 10 Ill.
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  • 78
    Digitale Medien
    Digitale Medien
    High pressure disruption of yeast cells: The use of scale down operations for the prediction of protein release and cell debris size distribution (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 642-649 
    Details
    ISSN: 0006-3592
    Schlagwort(e): scale-down ; homogenisation ; modelling ; size-distribution ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Experiments were carried out aimed at establishing the effects of equipment scale down on the disruption of Baker's yeast cells in high pressure homogenisers. Data are reported on the cell debris particle size distribution (PSD) and on total protein release as a function of the applied pressure for two valve geometries and three scales of operation covering flow rates of 28, 60 and 280 L/h. A comparison of the results from the experiments indicates that over the range of parameters investigated both the total protein release and the cell debris PSDs are independent of valve geometry and flow rate through the homogeniser. These observations are discussed in the light of relevant previous publications. The cell debris PSDs have been simulated by using a recently published model and the total protein release data are described by the well-established Hetherington expression (Hetherington et al., 1971). © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 642-649, 1997.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 79
    Digitale Medien
    Digitale Medien
    Dynamics of artificially immobilized Nitrosomonas europaea: Effect of biomass decay (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 630-641 
    Details
    ISSN: 0006-3592
    Schlagwort(e): nitrification ; immobilized cells ; Nitrosomonas europaea ; substrate limitation ; biomass death ; staining techniques ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The dynamics of growth and death of immobilized Nitrosomonas europaea were studied. For this, the death rate of suspended cells was determined in the absence of ammonium or oxygen by following the loss of respiration activity and by fluorescein-diacetate (FDA)/lissamine-green staining techniques. The death rates obtained (1.06 × 10-6 s-1 or 4.97 × 10-6 s-1 in the absence of oxygen or ammonium, respectively) were incorporated in a dynamic growth model and the effects on the performance of the immobilized-cell process illustrated by model simulations.These model simulations and experimental validation show that if decay of biomass occurs the biomass concentration in the center of the bead decreases. As a result, the systems react slower to changes in substrate concentrations than if all cells remain viable.To show that cells in the center of the bead died, the FDA and lissamine-green staining techniques were adapted for immobilized cells. It was shown that biomass decay occurred, especially in the center of the bead; the amount of cells decreased there, and the remaining cells were all stained with lissamine green indicating cell death. After the substrate availability was decreased, also cells near the surface of the bead lost their viability. The number of viable cells increased again after increasing the substrate concentration as the result of cell multiplication. At low substrate concentrations and low hydraulic retention times, as for example in the treatment of domestic wastewater, the death rate of cells is thus an important parameter for the performance of the immobilized-cell system. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 630-641, 1997.
    Zusätzliches Material: 6 Ill.
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  • 80
    Digitale Medien
    Digitale Medien
    Laboratory evaluation of a two-stage treatment system for TCE cometabolism by a methane-oxidizing mixed culture (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 650-659 
    Details
    ISSN: 0006-3592
    Schlagwort(e): cometabolism ; methanotroph ; trichloroethylene ; reactor ; aerobic ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The objective of this research was to evaluate several factors affecting the performance of a two-stage treatment system employing methane-oxidizing bacteria for trichloroethylene (TCE) biodegradation. The system consists of a completely mixed growth reactor and a plug-flow transformation reactor in which the TCE is cometabolized. Laboratory studies were conducted with continuous growth reactors and batch experiments simulating transformation reactor conditions. Performance was characterized in terms of TCE transformation capacity (TC, g TCE/g cells), transformation yield (TY, g TCE/g CH4), and the rate coefficient ratio kTCE/KS,TCE (L/mg-d). The growth reactor variables studied were solids retention time (SRT) and nutrient nitrogen (N) concentration. Formate and methane were evaluated as potential transformation reactor amendments. Comparison of cultures from 2- and 8-day SRT (nitrogen-limited) growth reactors indicated that there was no significant effect of growth reactor SRT or nitrogen availability on TC or TY, but N-limited conditions yielded higher kTCE/KS,TCE. The TCE cometabolic activity of the 8-day SRT, N-limited growth reactor culture varied significantly during a 7-year period of operation. The TC and TY of the resting cells increased gradually to levels a factor of 2 higher than the initial values. The reasons for this increase are unknown. Formate addition to the transformation reactor gave higher TC and TY for 2-day SRT growth reactor conditions and significantly lower TC, TY, and kTCE/KS,TCE for 8-day SRT N-limited conditions. Methane addition to the transformation reactor inhibited TCE cometabolism at low TCE concentrations and enhanced TCE cometabolism at high TCE concentrations, indicating that the TCE cometabolism in the presence of methane does not follow simple competitive inhibition kinetics. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 650-659, 1997.
    Zusätzliches Material: 7 Ill.
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  • 81
    Digitale Medien
    Digitale Medien
    Trichloroethylene mineralization in a fixed-film bioreactor using a pure culture expressing constitutively toluene ortho -monooxygenase (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 674-685 
    Details
    ISSN: 0006-3592
    Schlagwort(e): fixed-film bioreactor ; biofilter ; trichloroethylene ; mineralization ; toluene ortho -monooxygenase ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: An aerobic, single-pass, fixed-film bioreactor was designed for the continuous degradation and mineralization of gas-phase trichloroethylene (TCE). A pure culture of Burkholderia cepacia PR123(TOM23C), a Tn5transposon mutant of B. cepacia G4 that constitutively expresses the TCE-degrading enzyme, toluene ortho-monooxygenase (TOM), was immobilized on sintered glass (SIRAN™ carriers) and activated carbon. The inert open-pore structures of the sintered glass and the strongly, TCE-absorbing activated carbon provide a large surface area for biofilm development (2-8 mg total cellular protein/mL carrier with glucose minimal medium that lacks chloride ions). At gas-phase TCE concentrations ranging from 0.04 to 2.42 mg/L of air and 0.1 L/min of air flow, initial maximum TCE degradation rates of 0.007-0.715 nmol/(min mg protein) (equivalent to 8.6-392.3 mg TCE/L of reactor/day) were obtained. Using chloride ion generation as the indicator of TCE mineralization, the bioreactor with activated carbon mineralized an average of 6.9-10.3 mg TCE/L of reactor/day at 0.242 mg/L TCE concentration with 0.1 L/min of air flow for 38-40 days. Although these rates of TCE degradation and mineralization are two- to 200-fold higher than reported values, TOM was inactivated in the sintered-glass bioreactor at a rate that increased with increasing TCE concentration (e.g., in ∼2 days at 0.242 mg/L and 〈1 day at 2.42 mg/L), although the biofilter could be operated for longer periods at lower TCE concentrations. Using an oxygen probe and phenol as the substrate, the activity of TOM in the effluent cells of the bioreactor was monitored; the loss of TOM activity of the effluent cells corroborated the decrease in the TCE degradation and mineralization rates in the bioreactor. Repeated starving of the cells was found to restore TOM activity in the bioreactor with activated carbon and extended TCE mineralization by ∼34%. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 674-685, 1997.
    Zusätzliches Material: 6 Ill.
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  • 82
    Digitale Medien
    Digitale Medien
    Controlled biomass formation and kinetics of toluene degradation in a bioscrubber and in a reactor with a periodically moved trickle-bed (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 686-692 
    Details
    ISSN: 0006-3592
    Schlagwort(e): tolouene degradation ; biomass formation ; bioscrubber ; trickle-bed ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The kinetics of degradation of toluene from a model waste gas and of biomass formation were examined in a bioscrubber operated under different nutrient limitations with a mixed culture. The applicability of the kinetics of continuous cultivation of the mixed culture was examined for a special trickle-bed reactor with a periodically moved filter bed. The efficiency of toluene elimination of the bioscrubber was 50 to 57% and depended on the toluene mass transfer as evident from a constant productivity of 0.026 g dry cell weight/L · h over the dilution rate. Under potassium limitation the biomass productivity was reduced by 60% to 0.011 g dry cell weight/L · h at a dilution rate of 0.013/h. Conversely, at low dilution rates the specific toluene degradation rates increased. Excess biomass in a trickle-bed reactor causes reduction of interfacial area and mass transfer, and increase in pressure drop. To avoid these disadvantages, the trickle-bed was moved periodically and biomass was removed with outflowing medium. The concentration of steady state biomass fixed on polyamide beads decreased hyperbolically with the dilution rate. Also, the efficiency of toluene degradation decreased from 72 to 56% with increasing dilution rate while the productivity increased. Potassium limitation generally caused a reduction in biomass, productivity, and yield while the specific degradation increased with dilution rate. This allowed the application of the principles of the chemostat to the trickle-bed reactor described here, for toluene degradation from waste gases. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 686-692, 1997.
    Zusätzliches Material: 5 Ill.
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  • 83
    Digitale Medien
    Digitale Medien
    Macroporous chitin affinity membranes for lysozyme separation (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 610-617 
    Details
    ISSN: 0006-3592
    Schlagwort(e): chitin ; chitosan ; macroporous membranes ; affinity separation ; ovalbumin ; lysozyme ; egg white ; affinity membranes ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Macroporous chitin membranes with high, controlled porosity and good mechanical properties have been prepared using a technique developed in this laboratory based on silica particles as porogen. They were employed for the affinity separation of lysozyme. Chitin membranes (1 mm thickness) can be operated at high fluxes (≥1.1 mL/min/cm2) corresponding to pressure drops ≥2 psi. Their adsorption capacity for lysozyme (∼50 mg/mL membrane) is by an order of magnitude higher than that of the chitin beads employed in column separation. In a binary mixture of lysozyme and ovalbumin, the membranes showed very high selectivity towards lysozyme. The effect of some important operation parameters, such as the flow rates during loading and elution were investigated. Lysozyme of very high purity (〉98%) was obtained from a mixture of lysozyme and ovalbumin, and from egg white. The results indicate that the macroporous chitin membranes can be used for the separation, purification, and recovery of lysozyme at large scale. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 610-617, 1997.
    Zusätzliches Material: 9 Ill.
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  • 84
    Digitale Medien
    Digitale Medien
    An optimal strategy to model microbial growth in a multiple substrate environment (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 635-644 
    Details
    ISSN: 0006-3592
    Schlagwort(e): optimal growth ; flux towards growth ; E. coli K12 ; multiple substrate ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A comprehensive model is developed based on an optimal strategy describing varied microbial growth phenomenon involving sequential and simultaneous utilization of substrate. The model mimics the complex regulatory process of a cell which results in diverse growth process with the help of simple multi-variable constrained optimization, which aims at maximizing the specific cell growth. The metabolic processes of a cell are represented by simple flux balance equations. The different growth phenomenon exhibited by a microorganism are attributed to different levels of control present inside the cell. Provision is made in the model for these controls, in the form of constraints in the optimization formulation. The model prediction matches well with the experimental data of simultaneous growth of E. coli K12 on a mixture of glucose and organic acids like lactate, pyruvate, and acetate. Moreover, the model predictions are well in agreement with earlier published experimental data for the growth of E. coli K12 on other organic acids like fumarate, α-ketoglutarate, and succinate. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 635-644, 1997.
    Zusätzliches Material: 17 Ill.
    Materialart: Digitale Medien
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  • 85
    Digitale Medien
    Digitale Medien
    Substrate reactivity as a function of the extent of reaction in the enzymatic hydrolysis of lignocellulose (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 650-655 
    Details
    ISSN: 0006-3592
    Schlagwort(e): substrate reactivity ; lignocellulose ; cellulase ; pretreated wood ; property ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: In an effort to better understand the role of the substrate in the rapid fall off in the rate of enzymatic hydrolysis of cellulose with conversion, substrate reactivity was measured as a function of conversion. These measurements were made by interrupting the hydrolysis of pretreated wood at various degrees of conversion; and, after boiling and washing, restarting the hydrolysis in fresh buffer with fresh enzyme. The comparison of the restart rate per enzyme adsorbed with the initial rate per enzyme adsorbed, both extrapolated back to zero conversion, provides a measurement of the substrate reactivity without the complications of product inhibition or cellulase inactivation. The results indicate that the substrate reactivity falls only modestly as conversion increases. However, the restart rate is still higher than the rate of the uninterrupted hydrolysis, particularly at high conversion. Hence we conclude that the loss of substrate reactivity is not the principal cause for the long residence time required for complete conversion. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 650-655, 1997.
    Zusätzliches Material: 2 Ill.
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  • 86
    Digitale Medien
    Digitale Medien
    Synthesis of lovastatin with immobilized Candida rugosa lipase in organic solvents: Effects of reaction conditions on initial rates (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 671-680 
    Details
    ISSN: 0006-3592
    Schlagwort(e): immobilized enzymes ; Candida rugosa lipase ; organic solvents ; lovastatin ; dielectric constant ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Lipase from Candida rugosa immobilized on a nylon support has been used to synthesize lovastatin, a drug which lowers serum cholesterol levels, by the regioselective acylation of a diol lactone precursor with 2-methylbutyric acid in mixtures of organic solvents. Analogs of lovastatin having a different side chain were also obtained through this method by reacting the diol substrate with different carboxylic acids. The selection of reaction conditions that maximize the initial reaction rate is investigated. Since the diol substrate has very low solubility in non-polar solvents, reaction solvents consisting of mixtures of hexane with a different, more polar cosolvent are considered. For each of the cosolvent mixtures studied, the reaction rate is maximum for an intermediate percentage of cosolvent in hexane. With total concentrations of the diol lactone in the range 6.25-12.5 mM, maximum initial rates correspond approximately to those cosolvent concentrations that permit a complete solubilization of the substrate. At higher cosolvent concentrations, lower rates are obtained. When considering the same dissolved substrate concentration, the reaction rate was found to increase with increasing values of logPmix and decreasing values of the dielectric constant, when varying the composition of a binary solvent mixture. However, when comparing different cosolvents, no general trend with respect to these properties was observed. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56:671-680, 1997.
    Zusätzliches Material: 7 Ill.
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  • 87
    Digitale Medien
    Digitale Medien
    Effect of agitation intensities on fungal morphology of submerged fermentation (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 715-726 
    Details
    ISSN: 0006-3592
    Schlagwort(e): fungal morphology ; pellets ; hyphae ; hair of pellets ; agitation intensity ; fermentation ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Both parallel fermentations with Aspergillus awamori (CBS 115.52) and a literature study on several fungi have been carried out to determine a relation between fungal morphology and agitation intensity. The studied parameters include hyphal length, pellet size, surface structure or so-called hairy length of pellets, and dry mass per-wet-pellet volume at different specific energy dissipation rates. The literature data from different strains, different fermenters, and different cultivation conditions can be summarized to say that the main mean hyphal length is proportional to the specific energy dissipation rate according to a power function with an exponent of -0.25 ± 0.08. Fermentations with identical inocula showed that pellet size was also a function of the specific energy dissipation rate and proportional to the specific energy dissipation rate to an exponent of -0.16 ± 0.03. Based on the experimental observations, we propose the following mechanism of pellet damage during submerged cultivation in stirred fermenters. Interaction between mechanical forces and pellets results in the hyphal chip-off from the pellet outer zone instead of the breakup of pellets. By this mechanism, the extension of the hyphae or hair from pellets is restricted so that the size of pellets is related to the specific energy dissipation rate. Hyphae chipped off from pellets contribute free filamentous mycelia and reseed their growth. So the fraction of filamentous mycelial mass in the total biomass is related to the specific energy dissipation rate as well.To describe the surface morphology of pellets, the hyphal length in the outer zone of pellets or the so-called hairy length was measured in this study. A theoretical relation of the hairy length with the specific energy dissipation rate was derived. This relation matched the measured data well. It was found that the porosity of pellets showed an inverse relationship with the specific energy dissipation rate and that the dry biomass per-wet-pellet volume increased with the specific energy dissipation rates. This means that the tensile strength of pellets increased with the increase of specific energy dissipation rate. The assumption of a constant tensile strength, which is often used in literature, is then not valid for the derivation of the relation between pellet size and specific energy dissipation rate. The fraction of free filamentous mycelia in the total biomass appeared to be a function of the specific energy dissipation in stirred bioreactors. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 715-726, 1997.
    Zusätzliches Material: 13 Ill.
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  • 88
    Digitale Medien
    Digitale Medien
    Ammonium ion and glucosamine dependent increases of oligosaccharide complexity in recombinant glycoproteins secreted from cultivated BHK-21 cells (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 57 (1998), S. 518-528 
    Details
    ISSN: 0006-3592
    Schlagwort(e): ammonium ; UDP-GlcNAc ; N -glycosylation ; BHK-21 cells ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The effect of different ammonium concentrations and glucosamine on baby hamster kidney (BHK)-21 cell cultures grown in continuously perfused double membrane bioreactors was investigated with respect to the final carbohydrate structures of a secretory recombinant glycoprotein. The human interleukin-2 (IL-2) mutant glycoprotein variant IL-Mu6, which bears a novel N-glycosylation site (created by a single amino acid exchange of Gln100 to Asn), was produced under different defined protein-free culture conditions in the presence or absence of either glutamine, NH4Cl, or glucosamine. Recombinant glycoprotein products were purified and characterized by amino acid sequencing and carbohydrate structural analysis using matrix-assisted laser desorption ionization time of flight mass spectrometry, high-pH anion-exchange chromatography with pulsed amperometric detection, and methylation analysis. In the absence of glutamine, cells secreted glycoprotein forms with preponderantly biantennary, proximal fucosylated carbohydrate chains (85%) with a higher NeuAc content (58%). Under standard conditions in the presence of 7.5 mM glutamine, complex-type N-glycans were found to be mainly biantennary (68%) and triantennary structures (33%) with about 50% containing proximal α1-6-linked fucose; 37% of the antenna were found to be substituted with terminal α2-3-linked N-acetylneuraminic acid. In the presence of 15 mM exogenously added NH4Cl, a significant and reproducible increase in tri- and tetraantennary oligosaccharides (45% of total) was detected in the secretion product. In glutamin-free cultures supplemented with glucosamine, an intermediate amount of high antennary glycans was detected. The increase in complexity of N-linked oligosaccharides is considered to be brought about by the increased levels of intracellular uridine diphosphate-GlcNAc/GalNAc. These nucleotide sugar pools were found to be significantly elevated in the presence of high NH3/NH4+ and glucosamine concentrations. ©1998 John Wiley & Sons, Inc. Biotechnol Bioeng 57: 518-528, 1998.
    Zusätzliches Material: 5 Ill.
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  • 89
    Digitale Medien
    Digitale Medien
    Metabolic modeling of polyhydroxybutyrate biosynthesis (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 57 (1998), S. 557-570 
    Details
    ISSN: 0006-3592
    Schlagwort(e): Alcaligenes eutrophus ; polyhydroxyalkanoates ; metabolic engineering ; mathematical modeling ; enzyme kinetics ; regulation of metabolism ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A mathematical model describing intracellular polyhydroxybutyrate (PHB) synthesis in Alcaligenes eutrophus has been constructed. The model allows investigation of issues such as the existence of rate-limiting enzymatic steps, possible regulatory mechanisms in PHB synthesis, and the effects different types of rate expressions have on model behavior. Simulations with the model indicate that activities of all PHB pathway enzymes influence overall PHB flux and that no single enzymatic step can easily be identified as rate limiting. Simulations also support regulatory roles for both thiolase and reductase, mediated through AcCoA/CoASH and NADPH/NADP+ ratios, respectively. To make the model more realistic, complex rate expressions for enzyme-catalyzed reactions were used which reflect both the reversibility of the reactions and the reaction mechanisms. Use of the complex kinetic expressions dramatically changed the behavior of the system compared to a simple model containing only Michaelis-Menten kinetic expressions; the more complicated model displayed different responses to changes in enzyme activities as well as inhibition of flux by the reaction products CoASH and NADP+. These effects can be attributed to reversible rate expressions, which allow prediction of reaction rates under conditions both near and far from equilibrium. ©1998 John Wiley & Sons, Inc. Biotechnol Bioeng 57: 557-570, 1998.
    Zusätzliches Material: 7 Ill.
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  • 90
    Digitale Medien
    Digitale Medien
    Enhanced secretion of human granulocyte colony-stimulating factor directed by a novel hybrid fusion peptide from recombinant Saccharomyces cerevisiae at high cell concentration (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 57 (1998), S. 600-609 
    Details
    ISSN: 0006-3592
    Schlagwort(e): rhG-CSF ; fusion protein ; secretion efficiency ; glycosylation ; multimer ; conformation ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The synthesis and secretion of recombinant human granulocyte colony-stimulating factor (rhG-CSF) are investigated in fed-batch cultures at high cell concentration of recombinant Saccharomyces cerevisiae, and some important characteristics of the secreted rhG-CSF are demonstrated. Transcription of the recombinant gene is regulated by a GAL1-10 upstream activating sequence (UASG), and the rhG-CSF is expressed in a hybrid fusion protein consisting of signal sequence of Kluyveromyces lactis killer toxin and N-terminal 24 amino acids of human interleukin 1β. The intracellular KEX2 cleavage leads to excretion of mature rhG-CSF into extracellular culture broth, and the cleavage process seems to be highly efficient. In spite of relatively low copy number the plasmid propagation is stably maintained even at nonselective culture conditions. The rhG-CSF synthesis does not depend on galactose level, whereas the production of extracellular rhG-CSF was significantly enhanced by increasing the inducer concentration above a certain level and also by supplementing the nonionic surfactant to the culture medium, which is notably due to the enhanced secretion efficiency. Various immunoblotting analyses demonstrate that none of the rhG-CSF is accumulated in the cell wall fraction and that a significant amount of intracellular rhG-CSF antibody-specific immunoreactive proteins is located in the ER. A core N-glycosylation at fused IL-1β fragment is likely to play a critical role in directing the high-level secretion of rhG-CSF, and the O-glycosylation of secreted rhG-CSF seems nearly negligible. Also the extracellular rhG-CSF is observed to exist as various multimers, and the nature of molecular interaction is evidently not the covalent disulfide bridges. The CD spectra of purified rhG-CSF and Escherichia coli-derived standard show that the conformations of both are similar and are almost identical to that reported for natural hG-CSF. ©1998 John Wiley & Sons, Inc. Biotechnol Bioeng 57: 600-609, 1998.
    Zusätzliches Material: 8 Ill.
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  • 91
    Digitale Medien
    Digitale Medien
    Mathematical modeling of biofilm structure with a hybrid differential-discrete cellular automaton approach (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 58 (1998), S. 101-116 
    Details
    ISSN: 0006-3592
    Schlagwort(e): biofilm ; structure ; shape ; surface ; cellular automata ; discrete ; modeling ; roughness ; fractal ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A hybrid differential-discrete mathematical model has been used to simulate biofilm structures (surface shape, roughness, porosity) as a result of microbial growth in different environmental conditions. In this study, quantitative two- and three-dimensional models were evaluated by introducing statistical measures to characterize the complete biofilm structure, both the surface structure and volume structure. The surface enlargement, coefficient of roughness, fractal dimension of surface, biofilm compactness, and solids hold-up were found to be good measures of biofilm structure complexity. Among many possible factors affecting the biofilm structure, the influence of biomass growth in relation to the diffusive substrate transport was investigated. Porous biofilms, with many channels and voids between the “finger-like” or “mushroom” outgrowth, were obtained in a substrate-transport-limited regime. Conversely, compact and dense biofilms occurred in systems limited by the biomass growth rate and not by the substrate transfer rate. The surface complexity measures (enlargement, roughness, fractal dimension) all increased with increased transport limitation, whereas the volume measures (compactness, solid hold-up) decreased, showing the change from a compact and dense to a highly porous and open biofilm. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 58:101-116, 1998.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 92
    Digitale Medien
    Digitale Medien
    Analysis of endogenous process behavior in activated sludge (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 57 (1998), S. 155-163 
    Details
    ISSN: 0006-3592
    Schlagwort(e): endogenous respiration ; activated sludge ; multi-time scales ; identifiability ; observability ; model reduction ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: In this article, an autonomous four-compartment model that describes the endogenous respiration in an aerobic biodegradation process is proposed and analyzed theoretically. First, the multi-time scale of the system's behavior, to be taken into account in subsequent analyses, is emphasized. Then, an identifiability and observability study, given measurements of MLVSS (mixed liquor volatile suspended solids) and respiration rate, is performed for use under practical circumstances, such as in state and parameter estimation. It appears that the process is observable, but not fully identifiable. Hence, for the identification of some of the model parameters, additional measurements or experiments, also indicated here, have to be performed. Furthermore, it is shown that, under quasi-steady state conditions which, in general, appear shortly after initialization of an endogenous respiration experiment, the model can be reduced significantly. Finally, results of parameter estimation from available data are presented and discussed. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 57: 155-163, 1998.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 93
    Digitale Medien
    Digitale Medien
    Effect of extracellular glutamine concentration on primary and secondary metabolism of a murine hybridoma: An in vivo 13C nuclear magnetic resonance study (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 57 (1998), S. 172-186 
    Details
    ISSN: 0006-3592
    Schlagwort(e): hybridoma ; futile cycling ; hollow fiber bioreactor ; glutamine ; NMR ; C-13 ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The effect of changes in extracellular glutamine level on metabolism of a murine hybridoma was examined with in vivo nuclear magnetic resonance (NMR) spectroscopy. Cells were cultured in a hollow-fiber bioreactor at high cell density to allow intracellular metabolite levels to be determined on a metabolically relevant time scale. Steady infusions of [1-13C] glucose were used to label glycolytic and tricarboxylic acid cycle intermediates, which permitted continuous monitoring with NMR spectroscopy during changes in environmental glutamine level. Samples of the extracellular medium were also analyzed to determine the effect of glutamine on other metabolites associated with primary and secondary metabolism. The changes in glutamine concentration had several effects on primary and secondary metabolism, depending on the rate the changes were made. For a brief reduction in feed glutamine concentration from 4 to 0 mM (which produced a rapid change from 0.67 to ∼0 mM in residual glutamine), large changes were observed in the rate of consumption of metabolites normally associated with energy production. Antibody synthesis was strongly stimulated and nitrogen metabolism was significantly altered. For a more prolonged reduction from 2.4 to 1.2 mM (which produced a slower reduction from 0.30 to 0.08 mM in residual glutamine), much smaller changes were observed even though the concentration of glutamine at the reduced feed level was very low. Energy metabolism did not appear to be limited by glutamine at 0.08 mM, which suggests that significant futile cycling may occur in energy producing pathways when excess glucose and glutamine are available. However, this concentration of extracellular glutamine appeared to affect some anabolic pathways, which require amino groups from glutamine. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 57: 172-186, 1998.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 94
    Digitale Medien
    Digitale Medien
    Induction of catalytic activity in proteins by lyophilization in the presence of a transition state analogue (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 57 (1998), S. 211-215 
    Details
    ISSN: 0006-3592
    Schlagwort(e): protein ; conformational memory ; organic solvent ; molecular imprinting ; enzyme ; catalysis ; transition state analogue ; bovine serum albumin ; β-lactoglobulin ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The induction of catalytic activity in proteins by lyophilization in the presence of a transition state analogue (biomolecular imprinting) has been attempted. It was shown that proteins which were freeze-dried with n-isopropyl-4-nitrobenzyl-amine (a transition state analogue for the reaction of dehydrofluorination of 4-fluoro-4-[p-nitrophenyl] butan-2-one) displayed higher β-elimination activity as compared to their-non-imprinted counterparts. It was also found that native bovine serum albumin has a high dehydrofluorination activity towards the above substrate with kinetic parameters rather similar to those of a catalytic antibody prepared by Shokat et al. (1989). A comparison of the kinetic parameters determined in this study with those obtained for analogous catalytic antibodies and imprinted polymers was made. © 1998 John Wiley & Sons, Inc. Biotechnol. Bioeng. 57: 211-215, 1998.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 95
    Digitale Medien
    Digitale Medien
    Mobilization of broad host range plasmid from Pseudomonas putida to established biofilm of Bacillus azotoformans. I. Experiments (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 57 (1998), S. 272-279 
    Details
    ISSN: 0006-3592
    Schlagwort(e): biofilm ; plasmid transfer ; conjugation ; retrotransfer ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A strain of Pseudomonas putida harboring plasmids RK2 and pDLB101 was exposed to a pure culture biofilm of Bacillus azotoformans grown in a rotating annular reactor under three different concentrations of the limiting nutrient, succinate. Experimental results demonstrated that the broad host range RSF1010 derivative pDLB101 was transferred to and expressed by B. azotoformans. At the lower concentrations, donor mediated plasmid transfer increased with increasing nutrient levels, but the highest nutrient concentration yielded the lowest rate of donor to recipient plasmid transfer. For transconjugant initiated transfer, the rate of transfer increased with increasing nutrient concentrations for all cases. At the lower nutrient concentrations, the frequency of plasmid transfer was higher between donors and recipients than between transconjugants and recipients. The reverse was true at the highest succinate concentration. The rates and frequencies of plasmid transfer by mobilization were compared to gene exchange by retrotransfer. The initial rate of retrotransfer was slower than mobilization, but then increased dramatically. Retrotransfer produced a plasmid transfer frequency more than an order of magnitude higher than simple mobilization. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 57: 272-279, 1998.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 96
    Digitale Medien
    Digitale Medien
    Mobilization of broad host range plasmid from Pseudomonas putida to established biofilm of Bacillus azotoformans. II. Modeling (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 57 (1998), S. 280-286 
    Details
    ISSN: 0006-3592
    Schlagwort(e): biofilm ; plasmid transfer ; conjugation ; mathematical models ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A strain of Pseudomonas putida that harbors plasmids RK2 and pDLB101 was exposed to a pure culture biofilm of Bacillus azotoformans grown in a rotating annular reactor. Transfer of the RK2 mobilizable pDLB101 plasmid to B. azotoformans was monitored over a 4-day period. Experimental results demonstrated that the broad host range, RSF1010 derivative pDLB101 was transferred to and expressed by B. azotoformans. In the companion article to this work, the rate of plasmid transfer was quantified as a function of the limiting nutrient, succinate, and as a function of the mechanism of transfer. A biofilm process simulation program (AQUASIM) was modified to analyze resultant experimental data. Although the AQUASIM package was not designed to simulate or predict genetic events in biofilms, modification of the rate process dynamics allowed successful modeling of plasmid transfer. For the narrow range of substrate concentrations used in these experiments, nutrient level had only a slight effect on the rate and extent of plasmid transfer in biofilms. However, further simulations using AQUASIM revealed that under nutrient poor conditions, the number of transconjugants appearing in the biofilm was limited. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 57: 280-286, 1998.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 97
    Digitale Medien
    Digitale Medien
    Optimization of Phaffia rhodozyma continuous culture through response surface methodology (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 57 (1998), S. 314-320 
    Details
    ISSN: 0006-3592
    Schlagwort(e): Phaffia rhodozyma ; chemostat ; continuous fermentation ; astaxanthin ; peat ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Response surface methodology was applied to optimize the growth of the yeast Phaffia rhodozyma in continuous fermentation using peat hydrolysates as substrate. A second-order, complete, factorial design of the experiments was used to develop empirical models providing a quantitative interpretation of the relationships between the two variables studied, dilution rate and pH. Maximum biomass concentration in the fermentor was obtained by employing the following predicted optimum fermentation conditions: a dilution rate of 0.017/h and a pH level of 7.19. A verification experiment, conducted at previously optimized conditions for maximum biomass volumetric productivity (a dilution rate of 0.022/h, and a pH level of 6.90), produced values for biomass concentration, residual substrate concentration, biomass yield, and biomass volumetric productivity that were very close to the predicted values, indicating the reliability of the empirical model. The concentration of the pigment astaxanthin produced by the yeast under the optimized growth conditions was found to be 544 mg astaxanthin/kg dry cell biomass. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 57: 314-320, 1998.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 98
    Digitale Medien
    Digitale Medien
    Modeling brewers' yeast flocculation (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 57 (1998), S. 330-341 
    Details
    ISSN: 0006-3592
    Schlagwort(e): brewers' yeast ; collision theory ; flocculation ; modeling ; surface erosion ; floc splitting ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Flocculation of yeast cells occurs during the fermentation of beer. Partway through the fermentation the cells become flocculent and start to form flocs. If the environmental conditions, such as medium composition and fluid velocities in the tank, are optimal, the flocs will grow in size large enough to settle. After settling of the main part of the yeast the green beer is left, containing only a small amount of yeast necessary for rest conversions during the next process step, the lagering. The physical process of flocculation is a dynamic equilibrium of floc formation and floc breakup resulting in a bimodal size distribution containing single cells and flocs.The floc size distribution and the single cell amount were measured under the different conditions that occur during full scale fermentation. Influences on flocculation such as floc strength, specific power input, and total number of yeast cells in suspension were studied. A flocculation model was developed, and the measured data used for validation. Yeast floc formation can be described with the collision theory assuming a constant collision efficiency. The breakup of flocs appears to occur mainly via two mechanisms, the splitting of flocs and the erosion of yeast cells from the floc surface. The splitting rate determines the average floc size and the erosion rate determines the number of single cells. Regarding the size of the flocs with respect to the scale of turbulence, only the viscous subrange needs to be considered. With the model, the floc size distribution and the number of single cells can be predicted at a certain point during the fermentation. For this, the bond strength between the cells, the fractal dimension of the yeast, the specific power input in the tank and the number of yeast cells that are in suspension in the tank have to be known. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 57: 330-341, 1998.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 99
    Digitale Medien
    Digitale Medien
    Consecutive reaction kinetics involving distributed fraction of methanogens in fluidized-bed bioreactors (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 57 (1998), S. 367-379 
    Details
    ISSN: 0006-3592
    Schlagwort(e): fluidized-bed ; consecutive reaction kinetics ; distributed fraction of methanogens ; rate-limiting ; parametric sensitivity ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A kinetic model involving the distributed fractions of acidogens and methanogens is proposed. To determine the fluxes and biochemical reaction rates of the substrate sucrose and its intermediates, volatile fatty acids (VFAs) in bulk liquid and within the biofilm, a kinetic model was developed by combining the solid-phase model with the liquid-phase model. The predicted substrate removal efficiencies of the conventional and tapered fluidized-bed bioreactors (CFB, TFBs) are in good agreement with the experimental results. The biofilm thickness in TFBs are thicker than that in CFB, resulting in performance enhancement with TFBs. The simulated results obtained from the kinetic model show that methanogenesis is the rate-limiting step of degradation of the simple organic compound (sucrose), and the chemical oxygen demand (COD) concentration in the effluent is mainly contributed by the intermediates VFAs. The distributed fractions of acidogens and methanogens determined experimentally are 0.4 and 0.6, respectively. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 57: 367-379, 1998.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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    Artikel (Nationallizenzen)
  • 100
    Digitale Medien
    Digitale Medien
    A theoretical equation describing the time evolution of the concentration of a selected range of substrate molecular weights in depolymerization processes mediated by single-attack mechanism endo -enzymes (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 57 (1998), S. 387-393 
    Details
    ISSN: 0006-3592
    Schlagwort(e): depolymerization ; kinetics ; endo -enzymes ; theoretical equation ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Monitoring the time evolution of the concentration of a selected range of molecular weights of substrate, referred to as “detectable” substrate, has been used to determine endo-enzymic activities in polysaccharide depolymerizing processes. In the methodologies based on the use of dye-labeled substrates, the “detectable” substrate extends from a given molecular weight threshold downward. On the contrary, in the fluorescent probe-flow injection analysis methodology, initially developed to determine (1 → 3)-(1 → 4)-β-d-glucanase activities, the “detectable” substrate extends from a given molecular weight threshold upward. Assuming that the time evolution of the molecular weight distribution of the substrate follows the most probable distribution (the enzymic attack is random and its mechanism is single attack), a theoretical equation describing the time evolution of the concentration of “detectable” substrate (from a given molecular weight threshold upward or downward) has been deduced. This equation, Wd = Wo · (1 + αt) · e-αt, where Wd is the concentration of “detectable” substrate, Wo is the initial concentration of the substrate, t is the depolymerization time, and α is a parameter correlated through a hyperbola with the initial concentrations of enzyme and substrate and the Michaelis-Menten constant, Km, has been tested against different (1 → 3)-(1 → 4)-β-d-glucan/(1 → 3)-(1 → 4)-β-d-glucanase systems using the fluorescent probe-flow injection analysis methodology and Calcofluor as the fluorescent probe. The most important predictions of the theoretical equation, which allow accurate determination of both endo-enzymic activities and kinetic constants, have been experimentally confirmed. ©1998 John Wiley & Sons, Inc. Biotechnol Bioeng 57: 387-393, 1998.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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