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  • General Chemistry  (3,801)
  • Biochemistry and Biotechnology  (1,549)
  • Cell & Developmental Biology  (899)
  • Fluid Mechanics and Heat Transfer
  • 1995-1999  (6,694)
  • 1945-1949
  • 1997  (3,470)
  • 1996  (3,224)
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  • 1995-1999  (6,694)
  • 1945-1949
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  • 1
    Electronic Resource
    Electronic Resource
    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
    Keywords: gels ; electron microscopy ; scanning tunneling microscopy ; self-assembly ; ureas ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030811
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  • 2
    Electronic Resource
    Electronic Resource
    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
    Keywords: peptide bundles ; peptides ; pseudo-peptides ; template synthesis ; tripodal ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030813
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  • 3
    Electronic Resource
    Electronic Resource
    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
    Keywords: calixarenes ; hydrogen bonds ; molecular boxes ; noncovalent assembly ; supramolecular chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970031115
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  • 4
    Electronic Resource
    Electronic Resource
    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
    Keywords: disproportionations ; dithiocarba-mate ; homogeneous catalysis ; vulcanization ; zinc ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970031117
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  • 5
    Electronic Resource
    Electronic Resource
    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
    Keywords: conductivity ; europium ; gold ; magnetic properties ; superstructures ; tin ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970031118
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  • 6
    Electronic Resource
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    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
    Keywords: ab initio calculations ; aluminum ; boron ; pi interactions ; sulfur ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970031119
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  • 7
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    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 
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    ISSN: 0947-6539
    Keywords: immobilized catalysts ; polysiloxanes ; P ligands ; rhodium ; sol-gel processes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970031116
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  • 8
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    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
    Keywords: alkoxy radicals ; Barton reaction ; density functional calculations ; mass spectrometry ; radicals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970031120
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  • 9
    Electronic Resource
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    Asymmetric Addition Reactions with Optimized Selenium Electrophiles (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1894-1902 
    Details
    ISSN: 0947-6539
    Keywords: asymmetric synthesis ; chirality ; diselenides ; selenium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/chem.19970031123
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  • 10
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    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
    Keywords: heterocycles ; fluorine ; porphyrinoids ; zinc ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970031122
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  • 11
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    Cover page (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. cpi 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970031201
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  • 12
    Electronic Resource
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    Structure and Properties of Ba6Ni25S27 (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1884-1889 
    Details
    ISSN: 0947-6539
    Keywords: conducting materials ; electronic structure ; magnetic properties ; phase transitions ; sulfur ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970031121
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  • 13
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    Masthead (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997) 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970031202
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  • 14
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    Graphical abstract (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1911-1916 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970031203
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  • 15
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    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 
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    ISSN: 0947-6539
    Keywords: high-pressure chemistry ; high-temperature chemistry ; hydrogen ; Jupiter ; metallic hydrogen ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970031205
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  • 16
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    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 
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    ISSN: 0947-6539
    Keywords: combinatorial chemistry ; compound libraries ; drug research ; solid-phase synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970031204
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  • 17
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    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 
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    ISSN: 0947-6539
    Keywords: gas-phase chemistry ; interstellar chemistry ; ion-molecule reactions ; star formation ; surface chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970031207
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  • 18
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    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 
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    ISSN: 0947-6539
    Keywords: gas-phase chemistry ; interstellar chemistry ; kinetics ; low-temperature chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970031206
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  • 19
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    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
    Keywords: alkenes ; asymmetric synthesis ; natural products ; Lewis acids ; phosphane oxides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 4 Tab.
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    URL: http://dx.doi.org/10.1002/chem.19970031209
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    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
    Keywords: epothilone ; oxazoles ; cyclopropanes ; metathesis ; total synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970031211
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    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
    Keywords: catenanes ; molecular recognition ; pseudorotaxanes ; supramolecular chemistry ; translational isomerism ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 9 Ill.
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    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
    Keywords: clusters ; colloids ; gold ; nanostructures ; quantum wires ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970031210
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    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
    Keywords: epothilone ; oxazoles ; cyclopropanes ; total synthesis ; macrolactonizations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970031212
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    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
    Keywords: coordination polymers ; Prussian blue ; rhodium ; structure elucidation ; tin ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970031213
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    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
    Keywords: cyclic voltammetry ; logic gates ; molecular devices ; pseudorotaxanes ; spectroelectrochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1002/chem.19970031214
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    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
    Keywords: antisense agents ; chiral recognition ; oligonucleotides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1002/chem.19970031215
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    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 
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    ISSN: 0947-6539
    Keywords: arylphosphanes ; C-C coupling ; isotopic labeling ; palladium ; tin ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/chem.19970031219
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    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
    Keywords: carbohydrates ; correspondence ; dendrimers ; micelles ; nanospheres ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970031225
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    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 
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    ISSN: 0947-6539
    Keywords: chirality ; gas-phase chemistry ; ion-molecule reactions ; regioselectivity ; ring-opening reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1002/chem.19970031223
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    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
    Keywords: isocyanates ; „Jordan′s cation“ ; metallocenes ; peptides ; zirconium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1002/chem.19970030921
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    Cover page (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. cpi 
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    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 8 Ill.
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    Masthead (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997) 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970031002
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    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
    Keywords: C-H activation ; carbene complexes ; cycloadditions ; 1,3-diamino-1,3-butadiene ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    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 
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    ISSN: 0947-6539
    Keywords: carboxamides ; helical structures ; lanthanides ; luminescence ; tridentate ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1002/chem.19970031014
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    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 
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    ISSN: 0947-6539
    Keywords: cadmium sulfide ; catalysis ; photochemistry ; semiconductors ; unsaturated amines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    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 
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    ISSN: 0947-6539
    Keywords: glycals ; glycopeptides ; glycosylations ; β-mannosides ; oligosaccharides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    A Square As4 and a Prismatic As6 Structure as Complex Ligands (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1494-1498 
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    ISSN: 0947-6539
    Keywords: arsenic ; cobalt ; density functional calculations ; structural elucidation ; Zintl anions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: [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.
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    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 
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    ISSN: 0947-6539
    Keywords: duplex ; gel mobility ; nucleic acids ; oligonucleotides ; strand displacement ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    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
    Keywords: gadolinium ; NMR spectroscopy ; prototropic exchange ; rare earth compounds ; water exchange rate ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    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
    Keywords: conjugation length ; electrochemistry ; nonlinear optics ; oligomers ; poly-(triacetylene)s ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    Graphical abstract (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1552-1556 
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    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970031003
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    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
    Keywords: enzyme catalysis ; EXAFS spectroscopy ; heterogeneous catalysis ; synchrotron radiation ; X-ray absorption spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    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
    Keywords: arginine ; guanidines ; molecular recognition ; receptors ; supramolecular chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    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
    Keywords: catalysis ; chirality ; dendrimers ; molecular recognition ; surfaces ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    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
    Keywords: carbohydrates ; molecular modeling ; preorganization ; sialyl Lewisx ; selectins ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    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
    Keywords: adenine ; isomerizations ; NMR spectroscopy ; nucleotides ; stability constants ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    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 
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    ISSN: 0947-6539
    Keywords: alkylidene complexes ; lithium ; molybdenum ; nitric oxides ; tungsten ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: [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.
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    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 
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    ISSN: 0947-6539
    Keywords: azo compounds ; cycloadditions ; hydropyridazines ; pyrazolines ; rearrangements ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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).
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    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 
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    ISSN: 0947-6539
    Keywords: ab initio calculations ; hydrides ; osmium ; ruthenium ; silicon ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1002/chem.19970031010
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    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
    Keywords: DNA recognition ; hydrogen bonds ; ligand design ; molecular recognition ; sequence-specificity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1002/chem.19970031009
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    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
    Keywords: acetate ; anaerobic ; biodegradation ; formaldehyde ; methanogenic ; toxicity ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    Linear scale ultrafiltration (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 737-746 
    Details
    ISSN: 0006-3592
    Keywords: ultrafiltration ; scale-up ; scale-down ; linear scale ; proteins ; membrane fouling ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: subtilisin ; chymotrypsin ; substrate specificity ; organic solvents ; lyophilized enzymes ; stereoselectivity ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: Primatone RL ; sialylation ; interferon-γ ; serum substitutes ; cell ; CHO cell culture ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: insect cells ; baculovirus ; bcl-2 ; recombinant proteins ; cell viability ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: simple dissolution-reaction model ; enzymatic conversion ; solid substrate suspension ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: enzymatic fragment condensation ; α-chymotrypsin ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: transgenic plants ; recombinant protein ; gene expression ; downstream processing ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: ammonium ; cell culture ; cell cycle ; cell death ; cell growth ; Jurkat cells, GH4 cells ; LLC-PK1 cells ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: affinity ; separation ; purification ; continuous ; trypsin ; protein ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: affinity immobilization ; glycoenzymes ; thermal stability ; non-inhibitory antienzyme antibodies ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: albumin ; silicon ; hydrophobicity ; adsorption ; Tween 20 ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: sulphate reduction ; sulphite reduction ; biofilm ; immobilization ; gas-lift reactor ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: Citrobacter ; actinides ; nitrate ; biomineralization ; biocatalysis ; phosphatase ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: Catharanthus roseus ; hairy roots ; indole alkaloids ; organic acids ; nutrients ; growth association ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: virus ; antibody ; imaging ; real-time ; phage T7 ; diffusion ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: substrate-sufficient culture ; anabolism ; catabolism ; energy uncoupling ; growth yield ; residual substrate concentration ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: cumulative sedimentation analysis ; cell debris size ; Escherichia coli ; homogenization ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: hybridoma ; hypoosmotic stress ; specific antibody productivity ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: ethanol ; cellulose ; hemicellulose ; endoglucanase ; cellulase ; lignocellulose ; biomass ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: mRNA stability ; hairpins ; gene expression control ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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
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    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 
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    ISSN: 0006-3592
    Keywords: adsorptive membranes ; oscillatory flow ; integrated processes ; in situ product recovery ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: Saccharomyces cerevisiae ; metabolic modeling ; sensitivity analysis ; glycolysis ; compartmentation ; transient response ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: interacting populations ; membrane reactor ; induced metabolic changes ; elicitation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: cell adhesion ; radial-flow chamber ; hydrodynamic shear ; detachment kinetics ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: scale-down ; homogenisation ; modelling ; size-distribution ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: nitrification ; immobilized cells ; Nitrosomonas europaea ; substrate limitation ; biomass death ; staining techniques ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: cometabolism ; methanotroph ; trichloroethylene ; reactor ; aerobic ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: fixed-film bioreactor ; biofilter ; trichloroethylene ; mineralization ; toluene ortho -monooxygenase ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: tolouene degradation ; biomass formation ; bioscrubber ; trickle-bed ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: chitin ; chitosan ; macroporous membranes ; affinity separation ; ovalbumin ; lysozyme ; egg white ; affinity membranes ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: optimal growth ; flux towards growth ; E. coli K12 ; multiple substrate ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: substrate reactivity ; lignocellulose ; cellulase ; pretreated wood ; property ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: immobilized enzymes ; Candida rugosa lipase ; organic solvents ; lovastatin ; dielectric constant ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    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
    Keywords: fungal morphology ; pellets ; hyphae ; hair of pellets ; agitation intensity ; fermentation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
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    Dissolved hydrogen concentration as an on-line control parameter for the automated operation and optimization of anaerobic digesters (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 626-634 
    Details
    ISSN: 0006-3592
    Keywords: anaerobic digestion ; on-line control ; hydrogen concentration ; digester overloading ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The use of dissolved hydrogen as an early warning signal of digester failure and a control parameter to operate anaerobic digesters was investigated. A sensitive, on-line method was developed for measuring trace levels of dissolved hydrogen in a semi-permeable membrane, situated within the biomass of a 1 L laboratory anaerobic digester, using trace reduction gas analysis. At normal operating conditions, the dissolved hydrogen partial pressure (2 to 8 Pa) was found to be linearly correlated with the loading rate of the digester, and was a sensitive indicator of the effect of shockloads as well as gradual overloading. An increase in hydrogen partial pressure above a critical concentration of 6.5-7 Pa indicated the initial stage of digester overloading (i.e., volatile fatty acids accumulation). A H2-based computer control system, using a critical hydrogen partial pressure of 6.5 Pa as the setpoint, was found to be effective for the safe operation of a laboratory digester close to its maximum sustainable loading rate. The existence of a relationship between hydrogen level and organic loading rate was also confirmed on a 600 m3 industrial digester, with digester overloading occurring at hydrogen concentrations above 7 Pa. The results suggest that the dissolved hydrogen concentration is capable of being a sensitive on-line parameter for the automated management of anaerobic digesters near their maximum sustainable loading capacity. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 626-634, 1997.
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    Toluene diffusion and reaction in unsaturated Pseudomonas putida biofilms (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 656-670 
    Details
    ISSN: 0006-3592
    Keywords: unsaturated biofilm ; diffusion ; substrate utilization kinetics ; matric water potential ; toluene ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Biofilms are frequently studied in the context of submerged or aquatic systems. However, much less is known about biofilms in unsaturated systems, despite their importance to such processes as food spoilage, terrestrial nutrient cycling, and biodegradation of environmental pollutants in soils. Using modeling and experimentation, we have described the biodegradation of toluene in unsaturated media by bacterial biofilms as a function of matric water potential, a dominant variable in unsaturated systems. We experimentally determined diffusion and kinetic parameters for Pseudomonas putida biofilms, then predicted biodegradation rates over a range of matric water potentials. For validation, we measured the rate of toluene depletion by intact biofilms and found the results to reasonably follow the model predictions. The diffusion coefficient for toluene through unsaturated P. putida biofilm averaged 1.3 × 107 cm2/s, which is approximately two orders of magnitude lower than toluene diffusivity in water. Our studies show that, at the scale of the microbial biofilm, the diffusion of toluene to biodegrading bacteria can limit the overall rate of biological toluene depletion in unsaturated systems. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 656-670, 1997.
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    Experimental optimization of fed-batch culture for poly-β-hydroxybutyric acid production (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 697-705 
    Details
    ISSN: 0006-3592
    Keywords: poly-β-hydroxybutyric acid ; Alcaligenes eutrophus ; fed-batch culture ; high cell density culture ; optimization ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The optimal feed rate profiles of glucose and ammonium hydroxide were calculated using a proposed model, and implemented for the production of poly-β-hydroxybutyric acid (PHB) by Alcaligenes eutrophus. By implementing these optimal feed rates with a high glucose feed concentration of 700 g/L and an ammonium hydroxide concentration of 7%(w/w), it was possible to achieve a high final cell concentration of 141 g/L and a high PHB concentration of 105 g/L in 40 h of fed-batch operation. The PHB productivity was as high as 2.63 g/(L hr). © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 697-705, 1997.
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    Copper binding and release by immobilized transferrin: A new approach to heavy metal removal and recovery (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 01-09 
    Details
    ISSN: 0006-3592
    Keywords: transferrin ; conalbumin ; metalloprotein ; affinity chromatography ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Recently these laboratories have demonstrated that it is possible to use proteins as efficient, selective agents for heavy metal removal and recovery. In this study, transferrin was chemically bound to an insoluble support. The ability of immobilized transferrin to produce clean water was demonstrated. Copper loading was independent of feed concentration. The loaded copper could be readily eluted and concentrated into the gram per liter range. The mechanism of copper release was studied. It was shown that release was dependent on pH and the chelating ability of the stripping agent. Metal release occurred slowly at pH 〈 7. However, at low pH in the presence of a chelator, metal removal occurred much more efficiently. The binding constant of copper to immobilized transferrin was determined as a function of pH. This information was used to model metal binding and release to the protein/support matrix. © 1997 John Wiley & Sons, Inc.
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    Fouling effects of yeast culture with antifoam agents on microfilters (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 10-16 
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    ISSN: 0006-3592
    Keywords: microfiltration ; fouling ; yeast ; antifoam agents ; depressurization ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The fouling effects of yeast fermentation broths of Candida utilis in the presence of various commercial antifoam agents (PPG2000, B5600, and G832) up to 4.0 mL/L were studied, using Millipore polyvinylidene fluoride 0.22-μm hydrophilic membranes (GVWP), in a stirred-cell system at 50 kPa and 700 rpm. PPG2000, which has a low value of work of adhesion (Wa of 0.81 mN/m), gave a steady flux of broth of 29 L/(h m2) and was found to have no significant fouling effect on the microfiltration of broth. G832, which has a high Wa, (26.0 mN/m) reduced the flux of the broth to 17 L/(h m2); i.e., by 42% when only 1.0 mL/L was used. However, B5600, which has a Wa of 14.3 mN/m, was found to enhance the flux of broth to 54 L/(h m2); i.e., by 86%, due to the preferential adsorption of the B5600 components onto the hydrophobic cell contents released. These results were reinforced by the depressurization experiments performed with both hydrophilic (GVWP) and hydrophobic (GVHP) membranes, using both young and aged broths. B5600 was found to be the optimum antifoam agent in this study in terms of membrane performance and defoaming efficiency. © 1997 John Wiley & Sons, Inc.
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    Alginate oligosaccharides as enhancers of penicillin production in cultures of penicillium chrysogenum (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 17-20 
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    ISSN: 0006-3592
    Keywords: P. chrysogenum ; alginate oligosaccharides ; oligomannuronate ; oligoguluronate ; penicillin G ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Oligosaccharide fragments were prepared by partial acid hydrolysis of sodium alginate and consisted of oligomannuronate (OM) and oligoguluronate (OG) blocks. Effects of the OM and OG blocks on penicillin G production by P. chrysogenum were investigated. The oligosaccharides were found to cause significant increases in penicillin G yields. OM blocks at concentrations 10 to 100 μg/mL were used to further evaluate the effects of the oligosaccharides, and were found to enhance the production of penicillin G in shaken flask cultures of P. chrysogenum P2 (high penicillin producer) and NRRL 1951 (low penicillin producer) at the test concentrations. There was an approximately 50% maximum increase in penicillin G yield from biomass in P. chrysogenum P2 cultures and 150% in P. chrysogenum NRRL 1951 cultures, when compared to control cultures without the oligosaccharides. © 1997 John Wiley & Sons, Inc.
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    Effect of organic solvents on enantioselectivity of protease catalysis (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 26-31 
    Details
    ISSN: 0006-3592
    Keywords: protease ; transesterification ; enantioselectivity ; organic solvent ; solvent effect ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The protease-catalyzed transesterifications between N-trifluoroacetyl-DL-phenylalanine 2,2,2-trifluoroethyl ester and 1-propanol were studied in a variety of anhydrous organic solvents at 30°C. The protease preparations lyophilized from phosphate buffer solutions (pH 8.0) were used as catalysts. The organic solvent affected both rate of reaction and enantioselectivity differently. Proteases such as Aspergillus oryzae protease, subtilisin Carlsberg, and subtilisin BPN′ always preferred the L-enantiomer in both hydrophilic and hydrophobic solvents, indicating no inversion of the L-specificity in hydrophobic solvents such as toluene. However, enantioselectivity was rather poor, with E (enantiomeric ratio) values not exceeding even one order of magnitude except for acetonitrile. There was a weak inverse correlation between E values of subtilisin Carlsberg and solvent hydrophobicity (logP). Acetonitrile was a preferable solvent in terms of both rate of reaction and enantioselectivity (E= 15 to 25) for processing L-amino acid derivatives in organic media. Organic solvents generally have potential advantages of processing D-amino acid derivatives. © 1997 John Wiley & Sons, Inc.
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    Alcohol fermentation of starch by a genetic recombinant yeast having glucoamylase activity (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 21-25 
    Details
    ISSN: 0006-3592
    Keywords: starch fermentation ; recombinant yeast ; ethanol production ; glucoamylase activity ; fed-batch culture ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Alcohol fermentation of starch was investigated using a direct starch fermenting yeast, Saccharomyces cerevisiae SR93, constructed by integrating a glucoamylase-producing gene (STA1) into the chromosome of Saccharomyces cerevisiae SH1089. The glucoamylase was constitutively produced by the recombinant yeast. The ethanol concentration produced by the recombinant yeast was 14.3 g/L which was about 1.5-fold higher than by the conventional mixed culture using an amylolytic microorganism and a fermenting microorganism. About 60% of the starch was converted into ethanol by the recombinant yeast, and the ethanol yield reached its maximum value of 0.48 at the initial starch concentration of 50 g/L. The fed-batch culture, which maintains the starch concentration in the range of 30 to 50 g/L, was used to produce a large amount of ethanol from starch. The amount of ethanol produced in the fed-batch culture increased about 20% compared to the batch culture. © 1997 John Wiley & Sons, Inc.
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    Stability of nicotinamide adenine dinucleotide immobilized to cyanogen bromide activated agarose (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 41-48 
    Details
    ISSN: 0006-3592
    Keywords: nicotinamide adenine dinucleotide ; isourea ; imidocarbonate ; agarose ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The stability of NAD(H) immobilized to a crosslinked agarose support (Sepharose®-4B) was examined in buffer solutions at a pH of 7.0 and 8.5. Specifically, this study investigated particle attrition and ligand leakage rates from a cyanogen bromide activated agarose support. Particle attrition did not occur under the experimental conditions. Ligand leakage rates were found to be first order in immobilized ligand concentration with two labile populations of ligand. The two-population model is consistent with the cyanogen bromide coupling chemistry, which results in both an isourea and imidocarbonate ligand linkage. The rate of ligand leakage was found to occur over a time scale of days, with first order rate constants ranging from 0.007 to 0.15 d-1, depending on solution pH. © 1997 John Wiley & Sons, Inc.
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    Design and study of peptide-ligand affinity chromatography adsorbents: Application to the case of trypsin purification from bovine pancreas (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 49-57 
    Details
    ISSN: 0006-3592
    Keywords: chromatography ; enzyme purification ; peptide immobilization ; peptide ligand ; trypsin purification ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The purification of trypsin from bovine pancreas was employed in a case study concerning the design and optimization of peptide-ligand adsorbents for affinity chromatography. Four purpose-designed tripeptide-ligands were chemically synthesized (〉95% pure), exhibiting an Arg residue as their C-terminal (site P1) for trypsin bio-recognition, a Pro or Ala in site P2, and a Thr or Val in site P3. Each tripeptide-ligand was immobilized via its N-terminal amino group on Ultrogel A6R agarose gel, which was previously activated with low concentrations of cyanuric chloride (10.5 to 42.5 μmol/g gel). Well over 90% of the peptide used was immobilized. Three different concentrations were investigated for every immobilized tripeptide-ligand, 3.5, 7.0, and 14 μmol/g gel. The KD values of immobilized tripeptide-trypsin complexes were determined as well as the purifying performance and the trypsin-binding capacity of the affinity adsorbents. The KD values determined were in good agreement with the trypsin purification performance of the respective affinity adsorbents. The tripeptide sequence H-TPR-OH displayed the highest affinity for trypsin (KD 8.7 μM), whereas the sequence H-TAR-OH displayed the lowest (KD 38 μM). Dipeptide-ligands have failed to bind trypsin. When the ligand H-TPR-OH was immobilized via its N-terminal on agarose, at a concentration of 14 μmol/g gel, it produced the most effective affinity chromatography adsorbent. This adsorbent exhibited high trypsin-binding capacity (approximately 310,000 BAEE units/mL of adsorbent); furthermore, it purified trypsin from pancreatic crude extract to a specific activity of 15,200 BAEE units/mg (tenfold purification), and 82% yield. © 1997 John Wiley & Sons, Inc.
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    Performance of a sulfide-oxidizing expanded-bed reactor supplied with dissolved oxygen (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 32-40 
    Details
    ISSN: 0006-3592
    Keywords: expanded-bed reactor ; sulfur ; Thiobacilli ; immobilization ; biofilm ; sludge ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The performance of a new sulfide-oxidizing, expanded-bed bioreactor is described. To stimulate the formation of well-settleable sulfur sludge, which comprises active sulfide-oxidizing bacterial biomass and elemental sulfur, the aeration of the liquid phase and the oxidation of sulfide to elemental sulfur are spatially separated. The liquid phase is aerated in a vessel and subsequently recirculated to the sulfide-oxidizing bioreactor. In this manner, turbulencies due to aeration of the liquid phase in the bioreactor are avoided. It appeared that, under autotrophic conditions, almost all biomass present in the reactor will be immobilized within the sulfur sludge which consists mainly of elemental sulfur (92%) and biomass (2.5%). The particles formed have a diameter of up to 3 mm and can easily be grinded down. Within time, the sulfur sludge obtained excellent settling properties; e.g., after 50 days of operation, 90% of the sludge settles down at a velocity above 25 m h-1 while 10% of the sludge had a sedimentation velocity higher than 108 m h-1. Because the biomass is retained in the reactor, higher sulfide loading rates may be applied than to a conventional “free-cell” suspension. The maximum sulfide-loading rate reached was 14 g HS- L-1 d-1, whereas for a free-cell suspension a maximum loading rate of 6 g HS- L-1 d-1 was found. At higher loading rates, the upward velocities of the aerated suspension became too high so that sulfur sludge accumulated in the settling zone on top of the reactor. When the influent was supplemented with volatile fatty acids, heterotrophic sulfur and sulfate reducing bacteria, and possibly also (facultatively) heterotrophic Thiobacilli, accumulated within the sludge. This led to a serious deterioration of the system; i.e., the sulfur formed was increasingly reduced to sulfide, and also the formation rate of sulfur sludge declined. © 1997 John Wiley & Sons, Inc.
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    A Kalman filter algorithm and monitoring apparatus for at-line control of fractional protein precipitation (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 58-70 
    Details
    ISSN: 0006-3592
    Keywords: control ; monitoring ; fractional precipitation ; protein ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Downstream processing operations are often carried out blind in the process timescale since product monitoring on-line is not common. Knowledge of the location and concentration of the product and key contaminants is complementary to other process information for process development and, if available on-line in conjunction with a suitable model, control. This article sets out to demonstrate a model describing a two-cut fractional protein precipitation process and how this may be used for control of the process to maximize yield in the face of variable process stream conditions. Estimation of the model parameters is achieved by means of data-fitting by least squares and in comparison prediction by a Kalman filter algorithm. A description and error analysis of equipment for at-line monitoring of the soluble product in a pilot plant environment is presented which includes a micro-centrifuge necessary to clarify small volumes of sample prior to analysis. Finally, an account of the successful implementation of this equipment and the Kalman filter algorithm for control at bench scale is given where conditions in the process stream are deliberately disturbed to test the control operation. © 1997 John Wiley & Sons, Inc.
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    Effect of acetaldehyde on Saccharomyces cerevisiae and Zymomonas mobilis subjected to environmental shocks (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 71-78 
    Details
    ISSN: 0006-3592
    Keywords: Zymomonas ; yeast ; acetaldehyde ; ethanol ; stress ; inhibition ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The lag phase of Saccharomyces cerevisiae subjected to a step increase in temperature or ethanol concentration was reduced by as much as 60% when acetaldehyde was added to the medium at concentrations less than 0.1 g/L. Maximum specific growth rates were also substantially increased. Even greater proportional reductions in lag time due to acetaldehyde addition were observed for ethanol-shocked cultures of Zymomonas mobilis. Acetaldehyde had no effect on S. cerevisiae cultures started from stationary phase inocula in the absence of environmental shock and its lag-reducing effects were greater in complex medium than in a defined synthetic medium. Acetaldehyde reacted strongly with the ingredients of complex culture media. It is proposed that the effect of added acetaldehyde may be to compensate for the inability of cells to maintain transmembrane acetaldehyde gradients following an environmental shock. © 1997 John Wiley & Sons, Inc.
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    Preparation of magnetically susceptible polyacrylamide/magnetite beads for use in magnetically stabilized fluidized bed chromatography (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 79-87 
    Details
    ISSN: 0006-3592
    Keywords: polyacrylamide ; magnetic ; stabilized ; fluidized bed ; chromatography ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Spherical polyacrylamide/magnetite (PAM) composite beads, suitable for use in a magnetically stabilized fluidized bed (MSFB), were manufactured by a suspension polymerization method. Yield of beads depended on the type and concentration of buffer used during polymerization as well as the pH. More stabilizer was needed to prevent bead agglomeration as magnetite concentration increased. Bead diameter ranged from less than 60 to 600 μm, depending on reaction conditions, and the bead mean diameter and size distribution decreased with increasing impeller speed. The density and roundness factor of the beads were 1.19 ± 0.02 g cm-3 and 1.08 ± 0.03, respectively. The beads had high magnetization at a low applied magnetic field strength (60 mT at 75 kA m-1) and retained little residual magnetization (〈2 mT) after the field was removed. Incorporation of magnetite did not significantly affect the physical strength of the beads: the beads' average elastic modulus was 14 ± 4 kPa, similar to reported values for polyacrylamide gels (15.8 kPa). The beads were stable in a range of buffers from pH 1 to 10 and were resistant to microbial degradation. The fluidization and stabilization behavior of the beads was examined in a bench-scale MSFB. The minimum fluidization velocity (Umf) of the beads (0.035 mm s-1) allowed the MSFB to be operated at superficial velocities close to those used in HPLC systems. Against expectations, at high superficial velocities, the stabilized bed of the MSFB had a greater expansion than the unstabilized bed. The PAM beads could be derivatized and activated for soybean trypsin inhibitor immobilization by a standard carbodiimide method, and the affinity separation of trypsin from chymotrypsin was demonstrated. The PAM beads show excellent potential for use in MSFB chromatography. © 1997 John Wiley & Sons, Inc.
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    Abrasion of suspended biofilm pellets in airlift reactors: Importance of shape, structure, and particle concentrations (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 88-99 
    Details
    ISSN: 0006-3592
    Keywords: biofilm structure ; detachment ; abrasion ; collisions ; airlift-reactor ; hydrodynamics ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The detachment of biomass from suspended biofilm pellets in three-phase internal loop airlift reactors was investigated under nongrowth conditions and in the presence of bare carrier particles. In different sets of experiments, the concentrations of biofilm pellets and bare carrier particles were varied independently. Gas hold-up, bubble size, and general flow pattern were strongly influenced by changes in volume fractions of biofilm pellets and bare carrier particles. In spite of this, the rate of biomass detachment was found to be linear with both the concentration of biofilm pellets and the bare carrier concentration up to a solids hold-up of 30%. This implies that the detachment rate was dominated by collisions between biofilm pellets and bare carrier particles. These collisions caused an on-going abrasion of the biofilm pellets, leading to a reduction in pellet volume. Breakage of the biofilm pellets was negligible. The biofilm pellets were essentially ellipsoidal, which made three-dimensional size determination necessary. Calculating particle volumes from two-dimensional image analysis measurements and assuming a spherical shape led to serious errors. The abrasion rate was not equal on all sides of the biofilm pellets, resulting in an increasing flattening of the pellets. This flattening was oriented with the basalt carrier inside the biofilm and independent of the absolute abrasion rate. These observations suggest that the collisions causing abrasion are somehow oriented. The internal structure of the biofilms showed two layers, a cell-dense outer layer and an interior with a low biomass density. Taking this density gradient into account, the washout of detached biomass matched observed changes in volume of the biofilm pellets. No gradient in biofilm strength with biofilm depth was indicated. © 1997 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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