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  • NMR
  • Springer  (171)
  • Elsevier
  • Oxford University Press
  • 1995-1999  (171)
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  • 1
    Electronic Resource
    Electronic Resource
    The structure and conformation of the tryptophanyl diketopiperazines cyclo(Trp–Trp)·C2H6SO and cyclo(Trp–Pro) (1999)
    Springer
    Journal of chemical crystallography 29 (1999), S. 435-447 
    Details
    ISSN: 1572-8854
    Keywords: cyclic dipeptides ; Tryptophan ; Proline ; x-rays ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The structure and conformation of the cyclic dipeptides [cyclo(L-Trp–L-Trp)·C2H6SO] and cyclo(L-Trp–L-Pro) have been investigated with X-ray crystallographic and spectroscopic methods. Cyclo(L-tryptophanyl-L-tryptophanyl)·DMSO solvate crystallized in the space group P2 12121 with cell dimensions a = 6.193(2), b = 11.545(3), c = 31.117(4) Å. The crystal structure is stabilized by four hydrogen bonds (three intermolecular hydrogen bonds and one intramolecular bond). The first intermolecular bond is between the oxygen of DMSO and the nitrogen of indole ring 2, in contrast to the second intramolecular hydrogen bond between the nitrogen of indole ring 1 and the oxygen of DMSO. The two remaining intermolecular hydrogen bonds are between the nitrogens of the DKP ring and the carbonyl oxygens of the DKP ring. The values of χ1A 1 (−45.764) and χ1A 2 (67.437) indicate an extended side chain conformation for Trp residue 1 (EN) and a folded conformation for Trp residue 2. The DKP ring is more planar than in other cyclic dipeptide compounds (ϕ1 = 11.414, Ψ1 = −7.516, ϕ2 = 12.471, and Ψ2 = −8.256). In cyclo(L-Trp–L-Trp) the Cβ resonance of L-tryptophan (29.88 ppm) is shifted upfield 0.82 ppm when compared with the same resonance in cyclo(L-Trp–L-Gly) (30.7 ppm) and cyclo(L-Leu–L-Trp) (30.7 ppm). Two conformations of cyclo(Trp–Pro) crystallized in the space group P1 with cell dimensions a = 5.422(1), b = 9.902(1), c = 13.443(2) Å, α = 80.42(1), β = 78.61(1), and γ = 89.13(1)°. The conformation of the backbone and the orientation of the aromatic side chains for these conformers are very similar. The DKP rings for both conformers adopt a typical boat conformation in contrast to the flattened chair conformation observed for cyclo(Tyr–Pro) and cyclo(Phe–F-Pro). The tryptophan side chains of these conformers are folded towards the diketopiperazine (DKP) ring. The pyrrolidine ring for conformer 1 can be described as an envelope (Cs–Cβ-endo) conformation in contrast to the pyrrolidine ring symmetry for conformer 2 which is an intermediate between Cs and C2 rather than pure Cs for the proline ring with Cβ-endo and Cγ-exo with respect to C′. The two prolyl rings are puckered at the β-carbon atoms which deviate from the best planes defined by the four remaining atoms. The crystal structures are stabilized by four intermolecular hydrogens bonds. An intermolecular bond between the nitrogen of the indole ring (conformer 1) and the carbonyl oxygen of the DKP ring (conformer 2) was observed. The second hydrogen bond is between the nitrogen of the indole ring (conformer 2) and the carbonyl oxygen of the DKP ring (conformer 1). The last two hydrogens involve the carbonyl oxygens of the DKP rings and the nitrogens of the DKP rings [carbonyl oxygen of DKP ring (conformer 1)––––nitrogen of DKP ring (conformer 2); nitrogen of DKP ring (conformer 1)––––––carbonyl oxygen of DKP ring (conformer 2)].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009567127868
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  • 2
    Electronic Resource
    Electronic Resource
    A Direct Carbon-13 and Nitrogen-15 NMR Study of Cerium(III)–Isothiocyanate Complexation in Aqueous Solvent Mixtures (1999)
    Springer
    Journal of solution chemistry 28 (1999), S. 193-210 
    Details
    ISSN: 1572-8927
    Keywords: carbon-13 ; nitrogen-15 ; chlorine-35 ; NMR ; cerium(III)–isothiocyanate complexes ; water–acetone–Freon ; water–methanol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A study of lanthanide complexation with isothiocyanate is underway using a multinuclear magnetic resonance technique. For isothiocyanate solutions in water–acetone–Freon mixtures at low temperature, −85–−125°C, ligand exchange is slow enough to permit the observation of 13C and 15N NMR signals for coordinated and free anions. For the Ce3+–NCS− system, four coordinated anion signals, displaced from the free anion signal by about +450 to +550 ppm for 15N and +50 to +80 ppm for 13C, are observed. The 13C and 15N spectral data are complementary, showing a signal area concentration dependence and measured coordination numbers consistent with the formation of Ce(NCS)2+ through Ce(NCS)1- 4. In water–methanol, the extent of complexing is decreased, presumably because of the higher dielectric constant of this medium. In addition, the results of a competitive study of NCS− and Cl− ion binding, carried out using 35Cl NMR, is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1021754214188
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  • 3
    Electronic Resource
    Electronic Resource
    Molecular Modeling Study of the PtCl2 Complexes of Unsaturated S2On+1-Coronands: Dynamic Simulations and Investigation of the Ring Interconversion (1999)
    Springer
    Journal of molecular modeling 5 (1999), S. 72-77 
    Details
    ISSN: 0948-5023
    Keywords: Keywords Thiacrown ether ; NMR ; Pt(II) complexes ; Molecular dynamic simulations ; Ring interconversion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract   Maleonitrile-dithiacrown ethers mn-12S2O2 - mn-21S2O5 (mn = maleonitrile) are preorganized S2On+1-coronands (n = 1–4) which force B, AB and A class metal ions into mixed S/O coordination spheres. Moreover, they form chelate complexes with MX2 salts (M = Pd, Pt; X = Cl, Br), which were studied in this paper. The structures of mn-S2On+1 and [PtCl2(mn-S2On+1)] (n = 2, 3) were investigated theoretically by empirical and semiempirical methods using SYBYL (TRIPOS force field) and MSI/DISCOVER97 (ESFF force field). mn-12S2O2 was investigated experimentally by X-ray analysis and 1D and 2D NMR spectroscopy in solution and the complex formation was studied by 1H, 13C and 195Pt NMR titration experiments, respectively. S-inversion was also investigated in order to determine the ring corresponding interconversional barriers. Different orientations of the macrocyclic ring system mn-18S2O4 and of its transition states are shown.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s008940050106
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  • 4
    Electronic Resource
    Electronic Resource
    In situ MAS NMR investigations of molecular sieves and zeolite-catalyzed reactions (1999)
    Springer
    Catalysis letters 58 (1999), S. 1-19 
    Details
    ISSN: 1572-879X
    Keywords: zeolites ; chemicals ; NMR ; alkane activation ; reaction mechanism ; in situ investigation ; alkylation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Solid-state MAS NMR is a powerful technique to study heterogeneous catalysts and the way by which they operate. In situ MAS NMR has been demonstrated to be a powerful method to understand reaction mechanisms, to study the nature, dynamics and reactivity of surface intermediates and active sites, and to characterize structural modifications in the catalyst itself, in particular when using 13C strategically labelled substrates. In this paper, three examples selected from our own work are used to illustrate the potential of in situ MAS NMR. They are the formation of cumene and its isomerization to n-propylbenzene on zeolite H-ZSM-11, the activation of propane at low temperature and the alkylation of benzene with propane on zeolite H-ZSM-5, and the characterization of the aluminophosphate molecular sieve VPI-5 structure with temperature. Studies of the alkylation of benzene with propene confirmed that cumene was the primary reaction product. The undesired n-propylbenzene by-product results from the intermolecular reaction between cumene and benzene, enhanced by molecular shape-selective effects in medium pore size zeolites (e.g., H-ZSM-11). It explains why large pore zeolites, e.g., zeolite Beta, are used commercially today for this process. Propane can be activated at low temperature (ca. 573 K) on bifunctional medium pore size zeolites possessing intimately related acidic Brønsted sites and a dehydrogenation function provided by Ga or Zn species. In Ga/H-ZSM-5 catalysts, at 573 K, the activation of propane was shown to occur via a protonated pseudocyclopropane (PPCP) intermediate (or transition state). The latter evolves in a manner that can be formally described by the formation of CH 3 + , C2H 2 + , and C3H 7 + carbenium ion intermediates. These species can react with olefins, alkanes, or other electron-rich molecules such as benzene. The primary reaction products of the reaction of propane with benzene are n-propylbenzene (in small amount), ethylbenzene and toluene. Their subsequent reactions lead eventually to toluene and xylenes as the final products. In the structural characterization of VPI-5, 27Al, 31P, and 27Al nutation MAS NMR spectra show that, at 294 K, fully hydrated VPI-5 contains three equally populated Al and P crystallographic sites and that one-third of Al is 6-coordinate. The VPI-5 structure then belongs to the P63 space group. Above 353 K, VPI-5, fully or partially hydrated, undergoes a structural transformation to a higher framework symmetry, i.e., the P63cm space group. The transformation occurs at nearly the same temperature in both cases, indicating that the breakdown of the hydrogen-bonded helical water structure inside the VPI-5 pores is not a factor in the process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019044926400
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  • 5
    Electronic Resource
    Electronic Resource
    What do we know about the acidity of solid acids? (1999)
    Springer
    Catalysis letters 62 (1999), S. 1-13 
    Details
    ISSN: 1572-879X
    Keywords: acid catalysis ; zeolites ; temperature‐programmed desorption ; microcalorimetry ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract With a proper understanding of the nature of solid acidity, zeolites and other solid acids have great potential for replacing homogeneous acids in a wide range of catalytic applications. This paper describes results from our laboratory on the characterization and description of the acid sites in high‐silica zeolites, especially H‐MFI. A crucial observation from this work is the identification of stoichiometric adsorption complexes, one molecule per framework Al, for a wide range of adsorbates, including amines, alcohols, nitriles, ketones, and thiols. Examples are given in which temperature‐programmed desorption is used to identify these complexes and characterize their initial chemistries. Calorimetric measurements on the 1:1 complexes have been used to compare the enthalpies of protonation in the zeolite to enthalpies of protonation in the gas phase and in aqueous phase and to demonstrate that a gas‐phase basis provides better predictive capabilities. The issue of carbenium‐ion stabilities is discussed, as well as the unusual catalytic properties of acid sites formed by framework substitution of Fe. The effect of sorption and cavity size on reactions is described. Finally, the problems associated with trying to define or characterize solid acids by using ammonia TPD or 13C NMR isotropic shifts of ketones without proper consideration of the complicated nature of these techniques are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019010013989
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  • 6
    Electronic Resource
    Electronic Resource
    A 31P nuclear magnetic resonance study of phosphate levels in roots of ectomycorrhizal and nonmycorrhizal plants of Castanea sativa Mill. (1999)
    Springer
    Trees 13 (1999), S. 168-172 
    Details
    ISSN: 0931-1890
    Keywords: Key words Castanea sativa ; Pisolithus tinctorius ; Ectomycorrhiza ; Phosphate ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  31P-Nuclear Magnetic Resonance (NMR) was used to assess phosphate distribution in ectomycorrhizal and nonmycorrhizal roots of Castanea sativa Mill. as well as in the mycorrhizal fungus Pisolithus tinctorius in order to gain insight into phosphate trafficking in these systems. The fungus P. tinctorius accumulated high levels of polyphosphates during the rapid phase of growth. Mycorrhizal and nonmycorrhizal roots accumulate orthophosphate. Only mycorrhizal roots presented polyphosphates. The content in polyphosphates increased along the 3 months of mycorrhiza formation. In mycorrhizal roots of plants cultured under axenic conditions, the orthophosphate pool decreased along the culture time. In nonmycorrhizal roots the decrease in the orthophosphate content was less pronounced. The level of orthophosphate in mycorrhizal roots was significantly lower than in nonmycorrhizal ones, which indicates that this system relies upon the fungal polyphosphates as a major source of phosphate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00009748
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  • 7
    Electronic Resource
    Electronic Resource
    Solution structure of reduced horse heart cytochrome c (1999)
    Springer
    JBIC 4 (1999), S. 21-31 
    Details
    ISSN: 1432-1327
    Keywords: Key words Reduced cytochrome c ; Solution structure ; NMR ; Heme proteins ; Electron transfer proteins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  In the frame of a broad study on the structural differences between the two redox forms of cytochromes to be related to the electron transfer process, the NMR solution structure of horse heart cytochrome c in the reduced form has been determined. The structural data obtained in the present work are compared to those already available in the literature on the same protein and the presence of conformational differences is discussed in the light of the experimental method employed for the structure determination. Redox-state dependent changes are analyzed and in particular they are related to the role of propionate-7 of the heme. Also some hydrogen bonds are changed upon reduction of the heme iron. A substantial similarity is observed for the backbone fold, independently of the oxidation state. At variance, some meaningful differences are observed in the orientation of a few side chains. These changes are related to those found in the case of the highly homologous cytochrome c from Saccharomyces cerevisiae. The exchangeability of the NH protons has been investigated and found to be smaller than in the case of the oxidized protein. We think that this is a characteristic of reduced cytochromes and that mobility is a medium for molecular recognition in vivo.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007750050285
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  • 8
    Electronic Resource
    Electronic Resource
    Interaction of cis- and trans-RuCl2(DMSO)4 with the nucleotides GpA, d(GpA), ApG, d(ApG) and d(CCTGGTCC): high-field NMR characterization of the reaction products (1999)
    Springer
    JBIC 4 (1999), S. 199-208 
    Details
    ISSN: 1432-1327
    Keywords: Key words Ruthenium ; Nucleotides ; Dimethyl sulfoxide ; Anticancer ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  Both cis- and trans-RuCl2(DMSO)4 (cis-Ru and trans-Ru) react with ApG, GpA, d(ApG) and d(GpA) to yield products with bifunctional metal coordination of the bases. For each dinucleotide one major product and several minor species are formed. This is in contrast to previous results on analogous reactions between trans-Ru and d(GpG) where a substantial amount of an intermediate species was found. The rates of reaction between dinucleotides and cis-Ru are approximately 20-fold slower than for trans-Ru. The compounds formed with the two isomers exhibit identical proton NMR spectra, suggesting the same coordination mode for ruthenium in the final product. The two purine bases are coordinated to ruthenium through N7 in a head-to-head conformation with the glycosidic angles being in the anti range. Coupling constants indicate a relatively pure 3′-endo conformation for the 5′-sugar and mainly 2′-endo for the 3′-sugar. The similar bifunctional binding mode of cis- and trans-Ru(II) with dinucleotides as evident from the NMR spectra are in contrast to the different mode of interaction suggested earlier for cis- and trans-Ru complexes with DNA. trans-Ru interacts with the deoxyoctanucleotide d(CCTGGTCC), giving two main products during the first 2 h of incubation time. Four H8 guanine resonances are shifted downfield, characteristic of N7 metal coordination. The products are not analyzed in detail, but it is suggested that the structures may be described as two chiral G(N7/N7) chelates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007750050305
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  • 9
    Electronic Resource
    Electronic Resource
    The interactions of the N-terminal fusogenic peptide of HIV-1 gp41 with neutral phospholipids (1999)
    Springer
    European biophysics journal 28 (1999), S. 427-436 
    Details
    ISSN: 1432-1017
    Keywords: Key words HIV-1 fusion peptide ; EPR ; NMR ; Solid state NMR ; Circular dichroism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract We have studied the interactions with neutral phospholipid bilayers of FPI, the 23-residue fusogenic N-terminal peptide of the HIV-1LAI transmembrane glycoprotein gp41, by CD, EPR, NMR, and solid state NMR (SSNMR) with the objective of understanding how it lyses and fuses cells. Using small unilamellar vesicles made from egg yolk phoshatidylcholine which were not fused or permeabilised by the peptide we obtained results suggesting that it was capable of inserting as an α-helix into neutral phospholipid bilayers but was only completely monomeric at peptide/lipid (P/L) ratios of 1/2000 or lower. Above this value, mixed populations of monomeric and multimeric forms were found with the proportion of multimer increasing proportionally to P/L, as calculated from studies on the interaction between the peptide and spin-labelled phospholipid. The CD data indicated that, at P/L between 1/200 and 1/100, approximately 68% of the peptide appeared to be in α-helical form. When P/L=1/25 the α-helical content had decreased to 41%. Measurement at a P/L of 1/100 of the spin lattice relaxation effect on the 13C nuclei of the phospholipid acyl chains of an N-terminal spin label attached to the peptide showed that most of the peptide N-termini were located in the interior hydrocarbon region of the membrane. SSNMR on multilayers of ditetradecylphosphatidyl choline at P/Ls of 1/10, 1/20 and 1/30 showed that the peptide formed multimers that affected the motion of the lipid chains and disrupted the lipid alignment. We suggest that these aggregates may be relevant to the membrane-fusing and lytic activities of FPI and that they are worthy of further study.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002490050225
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  • 10
    Electronic Resource
    Electronic Resource
    The solution structure of a monomeric, reduced form of human copper,zinc superoxide dismutase bearing the same charge as the native protein (1999)
    Springer
    JBIC 4 (1999), S. 795-803 
    Details
    ISSN: 1432-1327
    Keywords: NMR ; Superoxide dismutase ; Solution structure ; Monomeric mutants ; Structure-function relationship
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: 2 , has RMSD values with respect to the average structure of 0.94 ± 0.14 Å2 and 1.50 ± 0.14 Å2 for the backbone and the heavy atoms, respectively. The overall folding, which includes the classical eight-stranded Greek-key β-barrel and a short α-helix, is very close to that of the previously characterized monomeric mutant E133QM2SOD and to that of wild-type SOD. The region involved in the subunit-subunit interactions in the dimeric protein is confirmed to be disordered in the monomeric species. It is also observed that a sizable rearrangement of the charged groups of the electrostatic loop and of Arg143 takes place in the monomeric species. The width of the active site channel, both at its entrance and at the bottleneck of the active site, is discussed in the light of the influence on the enzymatic activity and the latter with respect to the overall charge. It is also confirmed that the NH proton of His63 shields the Cu(I) from the bulk solvent, thus supporting the suggestion that superoxide may interact with the reduced metal ion in an outer-sphere fashion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007750050353
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  • 11
    Electronic Resource
    Electronic Resource
    Thermal Dehydration and Miscibility of PHEMA/PMAA Blends (1999)
    Springer
    Journal of thermal analysis and calorimetry 56 (1999), S. 1059-1063 
    Details
    ISSN: 1572-8943
    Keywords: dehydration ; miscibility ; NMR ; polymer blend ; poly(2-hydroxyethyl methacrylate) (PHEMA) ; poly(methacrylic acid) (PMAA) ; TG ; TMDSC
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Miscibility and dehydration of poly(2-hydroxyethyl methacrylate) and poly(methacrylic acid) (PHEMA/PMAA) blends were investigated by temperature modulated DSC (TMDSC), TG and solid-state 13C NMR methods. TMDSC spectra and 1H spin-relaxation times showed that the blends are homogeneous on a scale of 5-10 nm for all compositions. From TG and 13C NMR, we elucidated that the mass loss of the blends at 300°C is ascribed to the dehydration between the hydroxyl group of PHEMA and the carboxyl group of PMAA.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1010184323773
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  • 12
    Electronic Resource
    Electronic Resource
    An Improved Model for Predicting Proton NMR Shielding by Alkenes Based on Ab Initio GIAO Calculations (1999)
    Springer
    Structural chemistry 10 (1999), S. 375-380 
    Details
    ISSN: 1572-9001
    Keywords: Magnetic anisotropy ; NMR ; shielding cone ; isotropic shielding ; GIAO ; (de)shielding surface ; alkenes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In a strong magnetic field, nuclei located over a carbon-carbon double bond experience NMR shielding effects that are the net result of the magnetic anisotropy of the nearby double bond and various other intramolecular shielding effects. We have used GIAO, a subroutine in Gaussian 4, to calculate isotropic shielding values and to predict the proton NMR shielding increment for a simple model system: methane held in various orientations and positions over ethene. The average proton NMR shielding increments of several orientations of methane have been plotted versus the Cartesian coordinates of the methane protons relative to the center of ethene. A single empirical equation for predicting the NMR shielding experienced by protons over a carbon-carbon double bond has been developed from these data. The predictive capability of this equation has been validated by comparing the shielding increments for several alkenes calculated using our equation to the experimentally observed shielding increments. This equation predicts the NMR shielding effects more accurately than a previous model that was based on only one orientation of methane over ethene. Deshielding is predicted by this equation for protons over the center and within about 3 Å of a carbon-carbon double bond. This result is in contrast to predictions made by the long-held “shielding cone” model based on the McConnell equation found in nearly every textbook on NMR, but is consistent with experimental observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022095511927
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  • 13
    Electronic Resource
    Electronic Resource
    In situ NMR of heterogeneous catalysis: new methods and opportunities (1999)
    Springer
    Topics in catalysis 8 (1999), S. 81-86 
    Details
    ISSN: 1572-9028
    Keywords: NMR ; zeolite ; mechanism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In situ NMR has been extensively applied in the past decade to obtain basic mechanistic information about reactions in heterogeneous catalysis. Most studies in the literature have employed either sealed glass ampoules of catalyst and adsorbate that are heated outside of the NMR probe or variable temperature studies of samples sealed in magic‐angle spinning (MAS) rotors. In situ NMR studies of sealed samples fail to duplicate the conditions of temperature, reagent introduction and product removal found in bench‐top microreactor studies of catalysis. Previous attempts to more closely duplicate the conditions in flow reactors have motivated NMR studies using temperature jumps and the development of MAS probes with reagent flow. These methods have not yet achieved the time scales of several seconds or tenths of seconds that are typical of catalytic reactions. The pulse‐quench catalytic reactor has been developed to permit NMR studies of catalyst samples that have been prepared under actual reaction conditions. Pulse‐quench studies have provided evidence in support of a carbon‐pool mechanism for methanol‐to‐gasoline chemistry on HZSM‐5 and led to the identification of a pentamethylbenzenium cation formed in a zeolite by the alkylation of benzene with excess methanol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019140506645
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  • 14
    Electronic Resource
    Electronic Resource
    Synthesis of CIT-6, a zincosilicate with the *BEA topology (1999)
    Springer
    Topics in catalysis 9 (1999), S. 35-42 
    Details
    ISSN: 1572-9028
    Keywords: CIT-6 ; zincosilicate ; zinc beta ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A new, large pore zincosilicate denoted CIT-6 with the framework topology of zeolite beta has been synthesized from reaction mixtures containing Li+, Zn2+ and tetraethylammonium hydroxide (TEAOH) as a structure-directing agent (SDA). The effects of the concentrations of Li+, Zn2+ and TEAOH on the preparation of CIT-6 are investigated and it is shown that there are critical ranges in concentration for all three components for the crystallization of pure CIT-6. The incorporation of Zn2+ into the CIT-6 framework is confirmed by 29Si MAS-NMR and ion exchange results. CIT-6 is the first molecular sieve to contain framework zinc sites accessible to organic molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019150203436
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  • 15
    Electronic Resource
    Electronic Resource
    Structural Investigation of the First Stages of Pyrolysis of Si-C-O Preceramic Polymers Containing Si–H Bonds (1999)
    Springer
    Journal of sol gel science and technology 14 (1999), S. 39-48 
    Details
    ISSN: 1573-4846
    Keywords: polysiloxanes ; oxycarbide glasses ; NMR ; mass spectrometry ; pyrolysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The polymer-to-glass transformation in the Si-C-O system usually involves cross-linking reactions at the C sites, which transform for example ≡Si– $$\underline {\text{C}} $$ H3 sites into $$\underline {\text{C}} $$ (Si)4 sites, leading to the formation of a silicon oxycarbide network. Identification of the various C sites that form during pyrolysis under inert atmosphere is rather difficult from 13C MAS-NMR spectra, due to strong overlap of resonance lines, which prevents an accurate determination of the chemical shift values. This paper reports on the use of a spectral editing technique called Inversion Recovery Cross Polarization (IRCP), which, when combined with Cross Polarization (CP) technique, allows us to identify and quantify the formation of Si- $$\underline {\text{C}} $$ H2-Si bridges during the early stages of the pyrolytic transformation of a polysiloxane containing Si–CH3 and Si–H groups. Several Si-C-O systems characterized by the same initial number of Si–CH3 bonds but with increasing number of Si–H bonds, have been investigated by MAS-NMR as well as thermogravimetric analysis coupled with mass spectrometry (TG/MS). The Si—H bonds play clearly an active role in the insertion of C atoms within the silica network.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008771729921
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  • 16
    Electronic Resource
    Electronic Resource
    Silicon Oxycarbide Glasses (1999)
    Springer
    Journal of sol gel science and technology 14 (1999), S. 7-25 
    Details
    ISSN: 1573-4846
    Keywords: black glass ; silicon oxycarbide ; Nicalon ; NMR ; Raman ; TEM ; high temperature stability ; surface chemistry ; network carbon ; elemental carbon ; structure ; free carbon ; FTIR ; nanocomposite ; silicon carbide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The first attempts to introduce carbon into glass date back to 1951. But up until recently, the use of carbon or carbide raw materials, and the oxidation, volatilization and decomposition that accompany high temperature melting, have limited the synthesis of true silicon oxycarbide glasses. Here, the term silicon-oxycarbide refers specifically to a carbon-containing silicate glass wherein oxygen and carbon atoms share bonds with silicon in the amorphous, network structure. Thus, there is a distinction between black glass, which contains only a second-phase dispersion of elemental carbon, and oxycarbide glasses which usually contain both network carbon and elemental carbon. In addition to exploring the unique properties and applications of these glasses, per se, they are also of interest for developing models of the residual amorphous phases in polymer-derived silicon-carbide and silicon-nitride ceramics. The application of sol/gel techniques to glass synthesis has significantly advanced the development and characterization of silicon oxycarbide glasses. In this approach, alkyl-substituted silicon alkoxides, which are molecular precursors containing oxygen and carbon functionalities on the silicon, can be hydrolyzed and condensed without decomposition or loss of the carbon functional group. A low-temperature (〈1000°C) heat-treatment of the gel creates a glassy silicate material whose molecular structure consists of an oxygen/carbon anionic network. In addition, there is always a blackening of the material due to elemental carbon, which forms during pyrolysis and densification of the gel. The nature of the network carbon, and especially the distribution and form of the elemental carbon, are fundamental to the structure and properties of these novel materials. Their chemical and physical characteristics as revealed by NMR, Raman and TEM are discussed in the overview. In addition, the high temperature stability of these glasses (up to 1750°C), and the effect of hot-pressing, are described. It will be shown that the silicon oxycarbide network is stable up to 1000–1200°C. The network carbon is terminated with hydrogen (i.e., CH, =CH2 and –CH3), and with polyaromatic carbon (i.e., nC6Hx) wherein most of the elemental carbon resides. These glasses can be described as molecular composites of polyaromatic graphene-rings dispersed in a silicon oxycarbide network. After heating to temperatures in excess of 1000–1200°C, the oxycarbide network decomposes through the loss of hydrogen, and a two- or three-phase glass-ceramic consisting of nanocrystalline graphite, silicon carbide, and amorphous silica or cristobalite, is created. Some of the properties and applications of these glasses/glass-ceramics for coatings, composites and porous solids are summarized.
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    Topological structures of tetrahedral (Td and T) fullerenes with hexagonal and triangular faces and their vibration and NMR spectra (1999)
    Springer
    Theoretical chemistry accounts 102 (1999), S. 72-77 
    Details
    ISSN: 1432-2234
    Keywords: Key words: Fullerenes ; Tetrahedral symmetry ; IR active ; Raman active ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract. On analyzing the topological structures of the three types of tetrahedral fullerenes (which consist only of triangles and hexagons), (1) C n (T d ,n=12h 2; h=1,2,…), (2) C n (T d ,n=4h 2;h=1,2,…), and (3) C n (T,n=4(h 2+hk+k 2);h〉k,h,k=1,2,…), we have obtained theoretically the Infrared and Raman active modes by means of the derived formulas for the decomposition of their nuclear motions into irreducible representations, and the 13C NMR spectra with natural abundance for 13C by using the distribution functions for all of the tetrahedral (T d and T) fullerenes, respectively.
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    URL: http://dx.doi.org/10.1007/s002140050474
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    A novel cytokine-inducing glycolipid isolated from the lipoteichoic acid fraction of Enterococcus hirae ATCC 9790: A fundamental structure of the hydrophilic part (1999)
    Springer
    Glycoconjugate journal 16 (1999), S. 213-221 
    Details
    ISSN: 1573-4986
    Keywords: acetolysis ; IL-6 ; MALDI-TOF-MS ; mannan ; NMR ; poly(glycerophosphate) structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Previously, we showed that quantitatively minor several glycolipids only less than 5% of the lipoteichoic acid (LTA) fraction from Enterococcus hirae ATCC 9790 possessed cytokine-inducing activity, whereas the major component (over 90%) did not [Suda et al. (1995) FEMS Immun Med Microbiol 12:97–112]. The major inactive component was shown to have the chemical structure as was proposed for the LTA by Fischer [Hashimoto et al. (1997) J Biochem 121:779–86], suggesting that so-called LTA is not a cytokine-inducing component in the Gram-positive bacteria. In the present paper, the structure of the hydrophilic part of one of the cytokine-inducing glycolipid tentatively named GL4 is elucidated. GL4 was first subjected to hydrolysis with aqueous HF to give a polysaccharide and a mixture of low molecular weight products. The polysaccharide was composed mainly of highly branching mannan as concluded from NMR and MS analyses of its acetolysis products. The low molecular weight products consisted of phosphate and glycerol, suggesting the presence of a poly(glycerophosphate) structure in the original GL4. From these observations, the hydrophilic part of GL4 was shown to consist of mannose-rich polysaccharide and poly(glycerophosphate), the latter being bound to the former by a phosphodiester linkage.
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    Three-dimensional structure of scorpion toxins: Towards a new model of interaction with potassium channels (1999)
    Springer
    Perspectives in drug discovery and design 15-16 (1999), S. 41-60 
    Details
    ISSN: 1573-9023
    Keywords: dipole moment ; neurotoxin ; NMR ; potassium channel ; scorpion ; structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Scorpion venom contains various toxins which block ion-channels, responsible for either sodium, potassium, calcium or chloride membrane permeation. This review focuses on the three-dimensional structure of scorpion toxins specific for potassium channels, and on their structure–activity relationships. The overall fold of all these toxins is similar, despite their various specificities towards different types of potassium channels. Fine studies of the influence of punctual mutations of both toxins and channels have converged on a precise description of the scorpion toxins functional maps. From this knowledge, it now becomes possible to predict the specificity of a newly described scorpion toxin. The way is thus now open that leads to the design of new potent synthetic potassium channel blockers which in turn could be used as therapeutic drugs.
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    NMR Studies of Retinoid-Protein Interactions: The Conformation of [13C]-β-Ionones Bound to β-Lactoglobulin B (1999)
    Springer
    Pharmaceutical research 16 (1999), S. 651-659 
    Details
    ISSN: 1573-904X
    Keywords: 13C-edited ; NMR ; retinol ; retinoic acid ; β-lactoglobulin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. Vitamin A (retinol) and its metabolites comprise the natural retinoids. While the biological action of these molecules are thought to be primarily mediated by ca. 55 kDa nuclear retinoic acid receptors, a number of structurally similar 15-20 kDa proteins are involved in the transport, and possibly metabolism, of these compounds. The milk protein β-lactoglobulin B (β-LG) is an 18 kDa protein which binds retinol and may be involved in oral delivery of retinol to neonates. β-LG also binds drugs and other natural products and is of potential interest as a protective delivery vehicle. Methods. To examine the conformation of the model retinoid β-ionone both in solution and when bound to β-LG, NMR and computational methods have been employed. Results. Taken together, NMR studies of β-ionone in solution measuring scalar and dipolar coupling, as well as CHARMm calculations, suggest β-ionone prefers a slightly twisted 6-s-cis conformation. Isotope-edited NMR studies of l3C-labeled β-ionones bound to β-LG, primarily employing the HMQC-NOE experiment, suggest β-ionone also binds to β-LG in its 6-s-cis conformation. Conclusions. The methods employed here allow estimates of protein-bound ligand conformation. However, additional sites of ligand labeling will be necessary to aid in binding site localization.
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    NMR Investigations of the Inclusion of Thyroxine and Derivatives in Natural Cyclodextrins (1999)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 33 (1999), S. 307-319 
    Details
    ISSN: 1573-1111
    Keywords: cyclodextrins β and γ ; thyroxine ; thyroid hormones ; inclusion complex ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Thyroxine T4 and its derivatives (T3, T2) are very sparingly soluble in aqueous solutions even in the form of salts. In the presence of β or γ-cyclodextrins and in buffered basic solution, their solubilities are increased by inclusion in the cavity. The inclusion of these hormones in cyclodextrins was investigated by 1H-NMR in order to derive the influence of the number and position of the iodine atoms, and of the ionization state of the phenol group on the inclusion geometries.
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    A Quantum Chemical and Electrostatic Study of Alkyl and Substituted Benzenonium Cations and Related Molecules: The Effect of Atomic Charge Distribution on Carbocation Energy and Geometry (1999)
    Springer
    Structural chemistry 10 (1999), S. 121-127 
    Details
    ISSN: 1572-9001
    Keywords: NPA ; CHELPG ; MK ; AIM ; atomic charge ; NMR ; carbocation ; benzenonium ; electrostatic
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Geometries, NMR chemical shifts, atomic charges, and bond orders were calculated at the MP2/6-31G* level of theory for the isopropyl, sec-butyl, tert-butyl, benzenonium, and six methyl- and trifluoromethyl-substituted benzenonium ions. The NPA charges correlate better than the CHELPG, MK, and AIM charges with the experimental and calculated carbon chemical shifts. The electrostatic energies of isomeric ions, calculated by treatment of the NPA charges as point charges, are comparable to their MP2 energy differences. The electrostatic calculations, although classical approximations, provide a qualitative understanding of the coulombic basis of the methyl and trifluoromethyl substituent effects. It is apparent that these species are stabilized by having adjacent, oppositely charged atoms (for example, having the negatively charged carbon of a methyl group bonded to a positive carbon). It is proposed that a methyl group be termed a nucleophilic (rather than electron-donating) substituent and that a trifluoromethyl group be termed an electrophilic substituent. In the benzenonium ions and in toluene, fluoromethylbenzene, difluoromethylbenzene, and benzotrifluoride, the endocyclic angle at the substituent increases with increasing electrophilicity of the substituent. An electrostatic calculation again provides some insight into the coulombic basis of these changes.
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    NMR studies of interfaces, strain and anisotropy in Co/Cu multilayers (1999)
    Springer
    Hyperfine interactions 120-121 (1999), S. 23-30 
    Details
    ISSN: 1572-9540
    Keywords: NMR ; Co/Cu ; multilayers ; anisotropy ; 59Co
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract 59Co NMR studies of multilayers are able to give three direct pieces of information: (i) the crystal phase of Co, fcc (217.4 MHz), hcp (220–228 MHz) and in exotic cases bcc (198 MHz) for films measured at T= 4.2 K, (ii) the nature of the interfaces from low frequency satellite lines, and (iii) the strain state deduced from small changes in the line positions. Extensive studies of Co/Cu multilayer interfacial structures as a function of deposition technique, layer thickness, substrate/buffer layer structure and annealing temperature have been undertaken. This work has shed new light on the relationship between interfacial structure and magnetoresistance and in particular has demonstrated that flat, atomic scale, interfaces lead to greater magnetoresistance. The difference between the Co and Cu lattice constant results in an extensive, tensile in-plane strain developing in Co layers provided that some epitaxial registry is present. Information on strain effects can be obtained from the position and width of the NMR lines. The magnetic anisotropy field can be determined by measuring the field dependence of the enhancement effect due to electronic magnetisation. This provides unique insight into the distribution of magnetic anisotropy within the Co layers, as the enhancement can be investigated independently for each NMR line and, hence, provides environment specific information on magnetic anisotropy at the interfaces and in the interior of the layers.
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    Mammalian Exocrine Secretions. XII: Constituents of Interdigital Secretions of Bontebok, Damaliscus dorcas dorcas, and Blesbok, D. d. phillipsi (1999)
    Springer
    Journal of chemical ecology 25 (1999), S. 2057-2084 
    Details
    ISSN: 1573-1561
    Keywords: Damaliscus dorcas ; mammalian semiochemicals ; mammalian pheromones ; exocrine secretions ; interdigital secretions ; chemical communication ; mass spectrometry ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract In addition to the nine compounds identified in the interdigital secretion of the bontebok, Damaliscus dorcas dorcas, in a previous study, 76 compounds belonging to different compound types, were identified in the interdigital secretions of the bontebok and the blesbok, D. d. phillipsi. These compounds include alkanes, alcohols, aldehydes, ketones, fatty acids, terpenoids, γ-lactones, an isopropyl ester, long-chain hydroxyesters, 2-substituted pyridines, phenols, steroids, and dimethylsulfone. No qualitative differences were found between secretions from the two sexes or from animals from different habitats. Although no attempt was made to correlate territorial behavior or other behavioral phenomena with the qualitative composition of interdigital secretions from individual animals, available information seems to indicate that quantitative differences probably do not have a major semiochemical function. Only two species of bacteria, Bacillus brevis and Planococcus citreus, were found in the interdigital pouches of male and female members of the two subspecies, regardless of the habitat of the animals. B. brevis synthesized, among other unidentified constituents, (Z)-3-penten-2-ol, 2-hexanone, 2-octanone, 2-nonanone, tetradecanoic acid, pentadecanoic acid, heptadecanoic acid, octadecanoic acid, (Z)-9-hexadecenoic acid, and isopropyl hexadecanoate in vitro, while P. citreus produced, among others, the γ-lactones dodecan-4-olide and (Z)-6-dodecen-4-olide, which is one of the major constituents of the interdigital secretions of both subspecies. Some components of the interdigital secretions are not present in the interdigital glandular tissue, and the possibility is discused that these compounds could be produced by microbiological activity in the interdigital pouch.
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    Molecular Complex Formation between Some Azacrown Ethers and 2,4,6-Trinitrophenol (1999)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 34 (1999), S. 431-443 
    Details
    ISSN: 1573-1111
    Keywords: 2,4,6-trinitrophenol ; aza-crown ethers ; molecular complexes ; spectrophotometry ; IR ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The formation of molecular complexes with 1 : 1 stoichiometry between 2,4,6-trinitrophenol and aza-12-crown-4, aza-15-crown-5 and aza-18-crown-6 in chloroform solution was investigated spectrophotometrically. The resulting complexes were isolated and characterized by microchemical analysis, IR and NMR spectroscopy. The equilibrium constants of the 1 : 1 adducts were evaluated from the non-linear least-squares fitting of the absorbance-mole ratio data. The overall stability of the 2,4,6-trinitrophenol complexes was found to vary in the order aza-15-crown-5 〉 aza-18-crown-6 ≈ aza-12-crown-4. The kinetics of complex formation between 2,4,6-trinitrophenol and the aza-substituted crown ethers used were investigated and in all cases the results showed the occurrence of an oscillating chemical reaction in solution.
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    Structure of 2-acetoxy-3-(3-methoxy-4-acetoxy-5-chlorophenyl)-propenoic acid (1998)
    Springer
    Journal of chemical crystallography 28 (1998), S. 139-143 
    Details
    ISSN: 1572-8854
    Keywords: X-ray ; NMR ; enol acetate ; phenylpropenoic acid ; azlactone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract 2-Acetoxy-3-(3-methoxy-4-acetoxy-5-chlorophenyl)-propenoic acid 2 was synthesized from the azlactone of 5-chlorovanillin and its structure confirmed by X-ray crystallography and nuclear magnetic resonance methods. Compound 2 crystallized with a molecule of acetic acid in the P-1(#2) space group (Z = 2) and with cell dimensions a = 6.303(2), b = 9.779(1), c = 15.528(3) Å, α = 101.46(2), β = 100.71(2) and γ = 90.21(2)°. This study reveals the formation of an α-acetoxy propenoic acid with a trans extended side acid side chain conformation. The 1H and 13C NMR spectral values of 2 also show the existence of the enolic ester in solution.
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    Enol tautomer of the acetate ester of 3-methoxy-4-hydroxyphenylpyruvic acid: Crystallographic and NMR spectroscopic evidence (1998)
    Springer
    Journal of chemical crystallography 28 (1998), S. 193-196 
    Details
    ISSN: 1572-8854
    Keywords: x-ray ; NMR ; tautomerism ; enolate ; phenylpyruvic acid ; vanillin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The para acetate ester azlactone of vanillin 2 was synthesized from vanillin 1 and hydrolyzed with sodium hydroxide. The yielded product 3 was investigated with X-ray Crystallographic and nuclear magnetic resonance techniques. Compound 3 crystallized in the orthorhombic Pbca space group (Z = 8) and with cell dimensions a = 14.732(2), b = 12.756(3), c = 12.747(6)Å revealing the enolate tautomer and not the keto form of 3-methoxy-4-hydroxyphenylpyruvic acid as the acetate ester. The structure exhibited the pyruvic acid side chain in the trans extended conformation. A single proton on the benzylic carbon atom further suggested the existence of the enolate tautomer form of 3 in solution. The chemical shift values and peak integration in the NMR spectra add additional support to this finding.
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    Structure of 4-(2-chloro-4,5-dimethoxybenzylidene)-2-methyl-5-oxazolone. X-ray and NMR study (1998)
    Springer
    Journal of chemical crystallography 28 (1998), S. 811-814 
    Details
    ISSN: 1572-8854
    Keywords: X-ray ; NMR ; Z-isomer ; azlactone ; veratraldehyde
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The azlactone of 6-chloroveratraldehyde 3 (4-(2-chloro-4,5-dimethoxybenzylidene)-2-methyl-5-oxazolone) was synthesized from 6-chloroveratraldehyde 2 and its structure investigated using X-ray crystallographic and nuclear magnetic resonance methods. Compound 3 crystallized in the P21/c (#14) space group (Z = 4) with cell dimensions a = 9.148(2), b = 22.938(2), c = 6.707(1) Å, and β = 111.50(2)°. The X-ray study shows that azlactone 3 exists as the Z-isomer and crystallizes as a planar structure, i.e., both the phenyl and azlactone ring systems, as well as the functional groups attached to them, lie in the same plane. The 1H and 13C NMR spectral values also support the formation of the Z-isomer only, during the synthesis of 4-(2-chloro-4,5-dimethoxybenzylidene)-2-methyl-5-oxazolone.
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    Formation of Platinum–Tin Bond by Tin(II)Chloride Insertion (1998)
    Springer
    Journal of cluster science 9 (1998), S. 321-328 
    Details
    ISSN: 1572-8862
    Keywords: NMR ; tin(II)chloride ; insertion ; platinum ; platinum–tin bond
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The first 119Sn NMR evidence for the presence of direct platinum–tin bond in solution has been obtained for PtCl(SnCl3)(bdpp) complex (bdpp = (2S,4S)-2,4-bis(diphenylphosphino)pentane). Various PtCl2(L2) complexes (L2 = heterobidentate P−P, P−O, P−N, P−S chelating ligands) have been reacted with tin(II)chloride resulting in the formation of the corresponding PtCl(SnCl3)(L2) derivatives. Tin(II)chloride has been inserted into the Pt−Cl bond transto the harder donor atom of the L2 ligand.
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    Interaction of Cu(II) 3,5-diisopropylsalicylate with human serum albumin - an evaluation of spectroscopic data (1998)
    Springer
    BioMetals 11 (1998), S. 21-26 
    Details
    ISSN: 1572-8773
    Keywords: copper(II) 3,5-diisopropylsalicylate ; EPR ; human serum albumin ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The copper(II) complex of 3,5-diisopropylsalicylate is a lipophilic water-insoluble binuclear complex, Cu(II) (3,5-DIPS) , that has attracted interest because of a wide range of pharmacological activities. This study was undertaken to examine bonding interactions between the complex and human serum albumin (HSA) to help elucidate the mode of transport of the complex in vivo. Electron paramagnetic resonance, numerical magnetic resonance and UV-visible absorption spectroscopic studies were performed using 200 μM aqueous solutions (pH 7.5) of HSA to which had been added up to three molar equivalents of CuCl , CuSO , or Cu(II) (3,5-DIPS). Both EPR and UV-visible spectra demonstrated the presence of more than one copper bonding site on HSA, and proton NMR spectra showed that the 3,5-DIPS ligand is also bonded to HSA. These results indicate that there is no observable direct coordination of the ligand to copper in the presence of HSA, and that the majority of the copper and 3,5-DIPS bond to HSA at separate sites. Addition of solid Cu(II) (3,5-DIPS) to HSA at pH 7.5 similarly resulted in spectra that suggest that there are no ternary Cu(II)(3,5-DIPS), Cu(II)(3,5-DIPS) , or Cu(II) (3,5-DIPS) complexes formed with HSA. It is concluded that any ternary complexes formed in the presence of HSA are below the spectroscopic detection limits and represent less than 5% of the total copper. © Rapid Science 1998.
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    Interaction of aluminum ion with ATP. Mechanism of the aluminum inhibition of glycerol kinase and its reversal by spermine (1998)
    Springer
    BioMetals 11 (1998), S. 63-67 
    Details
    ISSN: 1572-8773
    Keywords: aluminum ion ; glycerol kinase ; NMR ; spermine ; yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Aluminum ion inhibited yeast glycerol kinase competitively with respect to the substrate MgATP. The K value of the enzyme for aluminum ion was about 3 μM. Spermine at physiological concentrations prevented glycerol kinase from the inhibition by aluminum ion. Nuclear magnetic resonance spectroscopy showed the specific elimination by spermine of aluminum from the metal-ATP complex, but no dissociation of MgATP complex by spermine. Inhibition by aluminum ion of glycerol kinase as well as hexokinase can reduce the utilization of energy fuel in yeast. Change in polyamine concentration may control energy production in vivo, and is responsible for the development of age-related aluminum toxicity. © Rapid Science 1998.
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    1H-NMR Relaxation of Water Molecules in the Aqueous Microcrystalline Cellulose Suspension Systems and Their Viscosity (1998)
    Springer
    Cellulose 5 (1998), S. 231-247 
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    ISSN: 1572-882X
    Keywords: microcrystalline cellulose ; water ; bound water ; particle ; suspension ; spin-spin relaxation time ; NMR ; viscosity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract An intensive study for aqueous microcrystalline cellulose (MCC) suspensions was carried out in view of the relationship between a viscosity and a 1H spin-spin relaxation time (T2) of water. An investigation was carried out for four suspension systems with the different particle size distributions. The proton mole ratio (α) of bound water against MCC particles and T2 of bound water (T2,b) were evaluated from the T2 values obtained by Carr-Purcell- Meiboom-Gill (C.P.M.G) method and those by solid echo method, respectively. As a result of these analyses, the T2,b value for the aqueous MCC suspension was evaluated as 5 × 10−3 s and it was found that the system having a larger α tended to show a higher viscosity. By relating the above results to the observation of the suspensions by an optical microscope, it was concluded that a network formed by MCC particles plays an important role in generating a high viscosity of MCC suspension, and that an averaged mobility of water molecules is sensitively affected by the network structure.
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    Multinuclear Magnetic Resonance Study of Zinc(II) and Cadmium(II) Complexing with Isothiocyanate (1998)
    Springer
    Journal of solution chemistry 27 (1998), S. 331-359 
    Details
    ISSN: 1572-8927
    Keywords: Hydrogen-1 ; carbon-13 ; nitrogen-15 ; cadmium-113 ; NMR ; infrared ; zinc(II) ; cadmium(II) ; isothiocyanate ; complexation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A study of zinc(II) and cadmium(II) complexes with isothiocyanate ion has been completed, using a low-temperature, multinuclear magnetic resonance technique that permits the observation of separate resonance signals for bound and free ligand, and Cd(II) metal ion. The Zn2+–NCS− complexes were studied by 1H, 13C, and 15N NMR spectroscopy. In the 1H spectra, the intensity of the coordinated water signal, corresponding to a Zn(II) hydration number of six in the absence of NCS−, decreases dramatically as this anion is added, indicating the complexing process involves more than a simple 1:1 ligand replacement. The 13C and 15N NMR spectra reveal signals for four species, most reasonably assigned to a series of tetrahedrally coordinated Zn2+–NCS− complexes. In the Cd2+–NCS− solution spectra, the 13C and 15N signals for four complexes also are observed and they are three line patterns, corresponding to a doublet from 113Cd J-coupling, and a dominant central peak, resulting from bonding to magnetically inactive Cd isotopes. The 113Cd spectra, showing signals for four complexes, correlate well in all respects with the 13C and 15N results, including coupling in specific cases. The spectral results for both metal ions reflect binding at the nitrogen atom of NCS−, with the complexes changing from an octahedral to a tetrahedral configuration when doing so. Confirming evidence for these conclusions also was provided by several infrared measurements of these metal–ion systems.
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    A Direct Carbon-13 and Nitrogen-15 NMR Study of Samarium(III)–Isothiocyanate Complexation in Aqueous Solvent Mixtures (1998)
    Springer
    Journal of solution chemistry 27 (1998), S. 581-600 
    Details
    ISSN: 1572-8927
    Keywords: Carbon-13 ; nitrogen-15 ; chlorine-35 ; NMR ; samarium(III) ; isothiocyanate ; Sm3+ − NCS− complexes ; water–acetone–Freon ; water–methanol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Multinuclear magnetic resonance studies of trivalent lanthanide inner-shell ion-pairing with nitrate and isothiocyanate are continuing. For NCS− solutions in water–acetone–Freon mixtures at low temperature, generally −100 to −125°C, ligand exchange is slow enough to permit the observation of 13C and 15N NMR signals for coordinated and free anions. For samariuni(III) solutions, four coordinated NCS−signals, displaced about +35 ppm and +250 ppm from free anion, are observed in the 13C and 15N NMR spectra, respectively. The 13C and 15N NMR data are complementary, showing a signal area concentration dependence and measured coordination numbers consistent with the formation of Sm(NCS)2+ through Sm(NCS) 4 1 . The coordination numbers reach a maximum of about three moles of NCS− per mole of Sm(III) with both nuclides, a result confirmed by spectral appearance showing the dominance of Sm(NCS)3 at the highest concentration studied. An analysis of the chemical shifts indicates that binding occurs at the nitrogen atom of NCS−. In water–methanol, due to the higher dielectric constant of such mixtures, coordination was less extensive. A competitive binding study with Ci− by 35Ci NMR demonstrated conclusively the superior coordinating ability of NCS−.
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    High resolution NMR techniques in catalysis (1998)
    Springer
    Topics in catalysis 5 (1998), S. 133-147 
    Details
    ISSN: 1572-9028
    Keywords: NMR ; catalysis ; high pressure ; dynamic equilibria ; magnetization transfer ; sapphire tube ; gas phase ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract High resolution NMR techniques are applicable to a variety of aspects of catalysis. Methods for studying homogeneously-catalyzed systems under high gas pressure are described along with approaches for obtaining mechanistic and dynamic information. Many of the same techniques may be applied to heterogeneous catalysis by following the reaction chemistry by gas phase NMR.
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    Metal ion binding to calmodulin: NMR and fluorescence studies (1998)
    Springer
    BioMetals 11 (1998), S. 213-222 
    Details
    ISSN: 1572-8773
    Keywords: calmodulin ; fluorescence spectroscopy ; metal ions ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Calmodulin is an important second messenger protein which is involved in a large variety of cellular path-ways.Calmodulin is sensitive to fluctuations in the intracellular Ca levels and is activated by the bindingof four Ca ions. In spite of the important role it plays in signal transduction pathways, it shows a surpris-inglybroad specificity for binding metal ions. Using 15N-Gly biosynthetically-labelled calmodulin, we havestudied the binding of different metal ions to calmodulin, including K+, Na+, Ca, Mg, Zn, Cd, Pb, Hg, Sr, La and Lu, by 1H, 15N HMQC NMR experiments. The effects of these ions on the substrate-bindingability of calmodulin have also been studied by fluorescence spectroscopy of the single tryptophan residue in a 22-residue synthetic peptide encompassing the skeletal muscle myosin light chain kinase calmod-ulin-binding domain. Most of these metal ions can activate a calmodulin target enzyme to some extent,though they bind to calmodulin in a different manner. Mg, which is of direct physiological interest, has adistinct site-preference for calmodulin, as it shows the highest affinity for site I in the N-terminal domain,while the C-terminal sites III and IV are the high affinity binding sites for Ca (as well as for Cd ). At ahigh concentration of Mg and a low concentration of Ca, calmodulin can bind Mg in its N-terminallobe while the C-terminal domain is occupied by Ca; this species could exist in resting cells in which the Mg level significantly exceeds that of Ca. Moreover, our data suggest that the toxicity of Pb-which,like Sr, binds with an equal and high affinity to all four sites-may be related to its capacity to tightlybind and improperly activate calmodulin.
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    Room-temperature formation of thermally stable aluminium-rich mesoporous MCM-41 (1998)
    Springer
    Catalysis letters 52 (1998), S. 21-23 
    Details
    ISSN: 1572-879X
    Keywords: RT synthesis ; thermal analysis ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The room-temperature (RT) synthesis of MCM-41 mesoporous compounds with high substitution levels of aluminium (Si / Al = 1.5) is achieved in a minimum time of synthesis. The compound shows similar characteristics to hydrothermally synthesized materials. 27Al NMR study confirms the presence of tetrahedral aluminium in as-synthesized material as well as in the calcined material without observing the presence of octahedral aluminium after calcination.
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    Biological, thermal and photochemical transformation of 2-trifluoromethylphenol (1998)
    Springer
    Biodegradation 9 (1998), S. 487-499 
    Details
    ISSN: 1572-9729
    Keywords: Bacillus ; biotransformation ; NMR ; thermophilic ; trifluoromethylphenol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract This is the first report on the metabolism of trifluoromethyl aromatics in a thermophilic bacterium, Bacillus thermoleovorans A2. Enzymes of the phenol degradation pathway are induced when cultivating Bacillus thermoleovorans A2 on complex medium. Direct measurements of fluorinated xenobiotics in cell suspensions using 19F-NMR made it possible to follow quantitatively the biotransformation routes. During the biotransformation of 2-CF3-phenol by B. thermoleovorans A2, a fluorinated metabolite, 2-hydroxy-6-oxo-7,7,7,-trifluorohepta-2,4-dienoate (7-TFHOD), accumulated. This metabolite is transformed non-enzymatically when exposed to sunlight. The accumulation of 7-TFHOD as an intermediate in the 2-CF3-phenol pathway was rationalized by calculating molecular properties of a series of meta-cleavage products.
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    On the detection of environmental effects on complex matrices combining off-line liquid chromatography and 1H-NMR (1998)
    Springer
    Biodegradation 9 (1998), S. 513-525 
    Details
    ISSN: 1572-9729
    Keywords: automation ; environment ; fingerprinting ; GLP ; LC ; NMR ; statistics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract An off-line combination of 400 MHz proton (1H)-NMR spectroscopy and liquid chromatography (LC) has been used for the multi-component comparison of low-molecular weight compounds (i.e., chemical fingerprinting) in model fluid broths and (processed) tomato. The focus of the research described is on (i) devising GLP-like methods for sample handling and NMR measurements that will ensure reproducibility, (ii) an automated handling of data, (iii) validity of the designed methodology and (iv) the interpretation of large amounts of data.
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    URL: http://dx.doi.org/10.1023/A:1008398321079
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    Modulation of Bacillus pasteurii cytochrome c 553 reduction potential by structural and solution parameters (1998)
    Springer
    JBIC 3 (1998), S. 371-382 
    Details
    ISSN: 1432-1327
    Keywords: Key words Bacillus pasteurii ; cytochrome c553 ; electrochemistry ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  Direct cyclic voltammetry and 1H NMR spectroscopy have been combined to investigate the electrochemical and spectroscopic properties of cytochrome c 553 isolated from the alkaliphilic soil bacterium Bacillus pasteurii. A quasi-reversible diffusion-controlled redox process is exhibited by cytochrome c 553 at a pyrolitic graphite edge microelectrode. The temperature dependence of the reduction potential, measured using a non-isothermal electrochemical cell, revealed a discontinuity at 308 K. The thermodynamic parameters determined in the low-temperature range (275–308 K;ΔS°′=–162.7±1.2 J mol–1 K–1, ΔH°′=–53.0±0.5 kJ mol–1, ΔG°′=–4.5±0.1 kJ mol–1, E°′=+47.0±0.6 mV) indicate the presence of large enthalpic and entropic effects, leading, respectively, to stabilization and destabilization of the reduced form of cytochrome c 553. Both effects are more accentuated in the high-temperature range (308–323 K;ΔS°′=–294.1±8.4 J mol–1 K–1, ΔH°′=–93.4±3.1 kJ mol–1, ΔG°′=–5.8±0.6 kJ mol–1, E°′=+60.3±5.8 mV), with the net result being a slight increase of the standard reduction potential. These thermodynamic parameters are interpreted using the compensation theory of hydration of biopolymers as indicating the extrusion, upon reduction, of water molecules from the hydration sphere of the cytochrome. The low-T and high-T conformers differ by the number of water molecules in the solvation sphere: in the high-T conformer, the number of water molecules extruded upon reduction increases, as compared to the low-T conformer. The ionic strength dependence of the reduction potential at 298 K, treated within the frame of extended Debye-Hückel theory, yields values of E °′ (I=0) =–25.4±1.4 mV, z red=–11.3, and z ox=–10.3. The pH dependence of the reduction potential at 298 K shows a plateau in the pH range 7–10 and an increase at more acidic pH, allowing the calculation of pK O=5.5 and pK R=5.7, together with the estimate of the reduction potentials of completely protonated (+71 mV) and deprotonated (+58 mV) forms of cytochrome c 553. 1H NMR spectra of the oxidized paramagnetic cytochrome c 553 indicate the presence of a His-Met axial coordination of the low-spin (S=1/2) heme iron, which is maintained in the temperature interval 288–340 K at pH 7 and in the pH range 4.8–10.0 at 298 K. The temperature dependence of the hyperfine-shifted signals shows both Curie-type and anti-Curie-type behavior, with marked deviations from linearity, interpreted as indicating the presence of a fast equilibrium between the low-T and high-T conformers, having slightly different heme electronic structures resulting from the T-induced conformational change. Increasing the NaCl concentration in the range 0–0.2 M causes a slight change of the 1H NMR chemical shifts of the hyperfine-shifted signals, with no influence on their linewidth. The calculated lower limit value of the apparent affinity constant for specific ion binding is estimated as 5.2±1.1 M–1. The pH dependence of the isotropically shifted 1H NMR signals of the oxidized cytochrome displays at least one ionization step with pK O=5.7. The thermodynamic and spectroscopic data indicate a large solvent-derived entropic effect as the main cause for the observed low reduction potential of B. pasteurii cytochrome c 553.
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    The effect of axial ligand plane orientation on the contact and pseudocontact shifts of low-spin ferriheme proteins (1998)
    Springer
    JBIC 3 (1998), S. 581-594 
    Details
    ISSN: 1432-1327
    Keywords: Key words Heme protein ; NMR ; paramagetic ; contact ; pseudocontact ; axial ligand
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  The effect of axial ligand nodal plane orientation on the contact and pseudocontact shifts of a symmetrical low-spin octamethylferriheme center has been calculated as a function of the angle of the axial ligand. Simple Hückel techniques have been used to estimate the contact contribution, and values obtained from model hemes, together with counter-rotation of the g-tensor, have been used to estimate the pseudocontact contribution, for the eight β-pyrrole methyl and four meso-H positions. It is found that the maximum and minimum contact shifts occur when the axial ligand is aligned at an angle of ±15° to the meso-H axes of the heme, rather than when the axial ligand plane lies along the porphyrin nitrogens, as assumed previously by some investigators. For systems having one planar axial ligand or two ligands in parallel planes, the contact and pseudocontact contributions at the meso-H positions are comparable in size (at least on the basis of simple Hückel estimates), while the contact contribution clearly dominates the isotropic shifts of the heme methyls. Allowing for the substituent effect of the 2,4-vinyls of protohemin, or the 2,4-thioethers of hemin c, as well as the average diamagnetic shifts of the heme methyls and meso-H, plots of the predicted shifts as a function of axial ligand nodal plane orientation have been constructed for hemin b- and c-containing proteins. Excellent agreement in the order of shifts, and reasonable agreement in the sizes of the observed shifts, is observed in the majority of the ferriheme proteins for which the methyl and meso-H resonances have been assigned and proton shifts reported. Plots have also been constructed for hemin c-containing proteins having the two axial ligand nodal planes oriented at relative angles of 40°, 70°, and 80°. Excellent agreement in the order of shifts, and reasonable agreement in the magnitudes of the observed shifts, is observed in all cases of bacterial cytochromes which do not fit the plots that assume the ligands are in parallel planes, except one – the cytochrome c-552 of Nitrosomonas europae. Except for this case, where the order of the predicted methyl shifts at any angle of the axial ligands disagrees with the observed, the reasons can usually be attributed to a large dihedral angle between two axial ligand nodal planes, to strong H-bonding interactions involving His and/or CN– ligands, or to off-axis binding of one (or both) axial ligand(s). Ruffling of the porphyrin ring may also contribute to the contact shift in as yet undefined ways. Hence, despite the simplicity of the calculations, the agreement with observed data is highly satisfying and the concept of the importance of axial ligand plane orientation on the observed proton shifts of heme proteins is fully confirmed.
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    Dodecylphosphocholine micelles as a membrane-like environment: new results from NMR relaxation and paramagnetic relaxation enhancement analysis (1998)
    Springer
    European biophysics journal 28 (1998), S. 48-58 
    Details
    ISSN: 1432-1017
    Keywords: Key words Dodecylphosphocholine ; Peptide-lipid interaction ; Paramagnetic probe ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract To further examine to what extent a dodecylphosphocholine (DPC) micelle mimics a phosphatidylcholine bilayer environment, we performed 13C, 2H, and 31P NMR relaxation measurements. Our data show that the dynamic behavior of DPC phosphocholine groups at low temperature (12 °C) corresponds to that of a phosphatidylcholine interface at high temperature (51 °C). In the presence of helical peptides, a PMP1 fragment, or an annexin fragment, the DPC local dynamics are not affected whereas the DPC aggregation number is increased to match an appropriate area/volume ratio for accommodating the bound peptides. We also show that quantitative measurements of paramagnetic relaxation enhancements induced by small amounts of spin-labeled phospholipids on peptide proton signals provide a meaningful insight on the location of both PMP1 and annexin fragments in DPC micelles. The paramagnetic contributions to the relaxation were extracted from intra-residue cross-peaks of NOESY spectra for both peptides. The location of each peptide in the micelles was found consistent with the corresponding relaxation data. As illustrated by the study of the PMP1 fragment, paramagnetic relaxation data also allow us to supply the missing medium-range NOEs and therefore to complete a standard conformational analysis of peptides in micelles.
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    URL: http://dx.doi.org/10.1007/s002490050182
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    Structure of the inactivating gate from the Shaker voltage gated K+ channel analyzed by NMR spectroscopy (1998)
    Springer
    European biophysics journal 27 (1998), S. 99-104 
    Details
    ISSN: 1432-1017
    Keywords: Key wordsShaker ; Potassium-channel ; NMR ; Structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Rapid inactivation of voltage-gated K+ (KV) channels is mediated by an N-terminal domain (inactivating ball domain) which blocks the open channel from the cytoplasmic side. Inactivating ball domains of various KV channels are also biologically active when synthesized separately and added as a peptide to the solution. Synthetic inactivating ball domains from different KV channels with hardly any sequence homology mediate quite similar effects even on unrelated KV channel subtypes whose inactivation domain has been deleted. The solution structure of the inactivating ball peptide from Shaker (Sh-P22) was analyzed with NMR spectroscopy. The NMR data indicate a non-random structure in an aqueous environment. However, while other inactivating ball peptides showed well-defined three-dimensional structures under these conditions, Sh-P22 does not have a unique, compactly folded structure in solution.
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    Determination of solution structures of paramagnetic proteins by NMR (1998)
    Springer
    European biophysics journal 27 (1998), S. 367-375 
    Details
    ISSN: 1432-1017
    Keywords: Key words Paramagnetic proteins ; Cytochromes ; Solution structure ; NMR ; Dipolar interactions ; Magnetic properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Standard procedures for using nuclear Overhauser enhancements (NOE) between protons to generate structures for diamagnetic proteins in solution from NMR data may be supplemented by using dipolar shifts if the protein is paramagnetic. This is advantageous since the electron-nuclear dipolar coupling provides relatively long-range geometric information with respect to the paramagnetic centre which complements the short-range distance constraints from NOEs. Several different strategies have been developed to date, but none of these attempts to combine data from NOEs and dipolar shifts in the initial stages of structure calculation or to determine three dimensional protein structures together with their magnetic properties. This work shows that the magnetic and atomic structures are highly correlated and that it is important to have additional constraints both to provide starting parameters for the magnetic properties and to improve the definition of the best fit. Useful parameters can be obtained for haem proteins from Fermi contact shifts; this approach is compared with a new method based on the analysis of dipolar shifts in haem methyl groups with respect to data from horse and tuna ferricytochromes c. The methods developed for using data from NOEs and dipolar shifts have been incorporated in a new computer program, PARADYANA, which is demonstrated in application to a model data set for the sequence of the haem octapeptide known as microperoxidase-8.
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    URL: http://dx.doi.org/10.1007/s002490050144
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    An Empirical Proton NMR Shielding Equation for Alkenes Based on Ab Initio Calculations (1998)
    Springer
    Structural chemistry 9 (1998), S. 403-410 
    Details
    ISSN: 1572-9001
    Keywords: Magnetic anisotropy ; NMR ; shielding cone ; shielding value ; GIAO ; ethene ; alkenes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Nuclei of hydrogen atoms located over a carbon-carbon double bond in the presence of a strong magnetic field experience a perturbed magnetic field caused primarily by the magnetic anisotropy of the π bond. However, the commonly used theoretical model for predicting the shielding effect of an alkene double bond on hydrogen nuclei is sometimes inconsistent with the observed proton NMR chemical shifts in structures that have covalently bonded hydrogens located over a carbon-carbon double bond. We have used the ab initio gauge including atomic orbital (GIAO) method to calculate isotropic shielding values and to determine the proton NMR shielding increments for a simple model system: methane held at various positions over ethene. These shielding increments calculated for one proton of methane have been mapped as a function of their position in Cartesian coordinates relative to the center of ethene. A mathematical function has been fit to this three-dimensional shielding increment surface at each of four distances from the face of the ethene molecule. Additionally, a single mathematical equation has been developed for predicting the shielding caused by the carbon-carbon double bond in ethene. In contrast to the traditionally employed shielding model, our results predict deshielding for protons within 3 Å above the center of a carbon-carbon double bond, consistent with experimental observations in several molecular systems. The NMR shielding increments predicted by this equation are compared to observed shielding increments in some test alkenes.
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    Structures and NMR Parameters of 1,2-Diphenylcyclobutanes (1998)
    Springer
    Structural chemistry 9 (1998), S. 419-427 
    Details
    ISSN: 1572-9001
    Keywords: NMR ; coupling constants ; cis and trans 1,2-diphenylcyclobutane ; angular dependence ; structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A new reaction scheme for obtaining cis and trans 1,2-diphenylcyclobutane is described. Using 1H-NMR at 600 MHz, full spectral assignment was made for both isomers, obtaining all J coupling constants and chemical shifts. NMR results on cis and trans 1,2-diphenylcyclobutane are compared with the vicinal coupling constants obtained by the Barfield–Smith equations from the literature internal and dihedral angles of cyclobutane. In the trans isomer, in agreement with previous results on halo-cyclobutanes, the conformation with the phenyls in the pseudo-di-equatorial position is strongly preferred. On the contrary, the cis isomer fluctuates between the two equivalent conformations: phenyl pseudo-axial and pseudo-equatorial.
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    Sulfide Gels and Films: Products of Non-Oxide Gelation (1998)
    Springer
    Journal of sol gel science and technology 13 (1998), S. 61-64 
    Details
    ISSN: 1573-4846
    Keywords: cadmium sulfide nanocrystals ; sol-gel transition ; aggregation ; NMR ; small angle X-ray scattering (SAXS) ; thin films
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The preparation of concentrated sols and transparent stiff gels of II-VI semiconductors nanocrystals is reported. A two-step process for the production of cadmium sulfide is reported. Sol stabilization and gelation control are achieved through successive passivation and depassivation of the surface of the nanocrystals which are complexed with thiols. The mechanisms driving the aggregation and the gelation are explained on the basis of NMR and SAXS experiments. Thin films as well as monoliths can be produced. The general principles of the method presented are not restricted to chalcogenide systems and thus enlarge the domain of application of the inorganic sol-gel process.
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    URL: http://dx.doi.org/10.1023/A:1008695003946
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    Hybrid Xerogel Structure and Molecular Guest Dynamics (1998)
    Springer
    Journal of sol gel science and technology 13 (1998), S. 457-460 
    Details
    ISSN: 1573-4846
    Keywords: hybrid organic-inorganic materials ; gel drying ; molecular dynamics ; NMR ; sol-gel transition ; confinement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A new experimental approach to study the porosity of hybrid organic-inorganic glasses is reported. It relies upon nuclear magnetic resonance observation of molecular guest dynamics. It is shown that in MTEOS xerogels, there exists an interconnected organic-rich network in which organic guests are trapped and can eventually diffuse. The interpore translational diffusion is strongly activated and its spatial extension gives information on the pore connectivity, whose decay is characterized by the interpore jump probability given by the theoretical model.
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    URL: http://dx.doi.org/10.1023/A:1008633630489
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    Correlations between 29Si, 17O and 1H NMR properties and local structures in silicates: an ab initio calculation (1998)
    Springer
    Physics and chemistry of minerals 26 (1998), S. 14-30 
    Details
    ISSN: 1432-2021
    Keywords: Key words ab initio ; NMR ; silicates ; structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract  In order to gain insight into the correlations between 29Si, 17O and 1H NMR properties (chemical shift and quadrupolar coupling parameters) and local structures in silicates, ab initio self-consistent field Hartree-Fock molecular orbital calculations have been carried out on silicate clusters of various polymerizations and intertetrahedral (Si-O-Si) angles. These include Si(OH)4 monomers (isolated as well as interacting), Si2O(OH)6 dimers (C2 symmetry) with the Si-O-Si angle fixed at 5° intervals from 120° to 180°, Si3O2(OH)8 linear trimers (C2 symmetry) with varying Si-O-Si angles, Si3O3(OH)6 three-membered rings (D3 and C1 symmetries), Si4O4(OH)8 four-membered ring (C4 symmetry) and Si8O12(OH)8 octamer (D4 symmetry). The calculated 29Si, 17O and 1H isotropic chemical shifts (δi Si, δi O and δi H) for these clusters are all close to experimental NMR data for similar local structures in crystalline silicates. The calculated 17O quadrupolar coupling constants (QCC) of the bridging oxygens (Si-O-Si) are also in good agreement with experimental data. The calculated 17O QCC of silanols (Si-O-H) are much larger than those of the bridging oxygens, but unfortunately there are no experimental data for similar groups in well-characterized crystalline phases for comparison. There is a good correlation between δi Si and the mean Si-O-Si angle for both Q 1 and Q 2, where Q n denotes Si with n other tetrahedral Si next-nearest neighbors. Both the δ i O and the 17O electric field gradient asymmetry parameter, η of the bridging oxygens have been found to depend strongly on the O site symmetry, in addition to the Si-O-Si angle. On the other hand, the 17O QCC seems to be influenced little by structural parameters other than the Si-O-Si angle, and is thus expected to be the most reliable 17O NMR parameter that can be used to decipher Si-O-Si angle distribution information. Both the 17O QCC and the 2H QCC of silanols decrease with decreasing length of hydrogen bond to a second O atom (Si-O-H···O), and the δ i H increase with the same parameter.
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    URL: http://dx.doi.org/10.1007/s002690050157
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    Conformational properties of a cyclic oligosaccharide: cyclotrikis-(1→6)-[α-D-glucopyranosyl-(1→4)-β-D-glucopyranosyl] (1998)
    Springer
    Glycoconjugate journal 15 (1998), S. 511-521 
    Details
    ISSN: 1573-4986
    Keywords: Monte Carlo ; NMR ; ROESY ; AMBER
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The title compound is a cyclic oligosaccharide having six glucopyranose residues linked alternatively by α-(1→4) and β-(1→6) glycosidic linkages. Like cyclodextrin analogues it is expected to exhibit an internal cavity and to form inclusion complexes with other species. In order to investigate its conformational preferences, an extensive conformational search was carried out using a combination of Metropolis Monte-Carlo (MMC) procedure in the glycosidic torsion angle space and molecular mechanics procedures. To this end a specific program (METROCYCLIX) was developed. To reduce the MMC search, conformational maps of parent disaccharides were considered as starting entries. Fully minimized conformations were gathered into families using a clustering technique based on RMS fitting over the glycosidic torsion angle values. A wide range of local energy minima were identified in spite of ring closure conditions that constrained the structure of the oligosaccharide. Low energy conformers were stabilized by intramolecular interactions between distant residues. From the Bolzmann population of the best structures derived from the clustering results, various average properties were calculated and compared with experimental data obtained by high resolution NMR. Interpretation of these experimental values (heteronuclear coupling constants, rotating frame nuclear Overhauser effects, relaxation times) relies on the use of Karplus like equations (coupling constants) and analysis of the full relaxation rate matrix treatment (ROE). The quality of the molecular modelling strategy used is assessed by the agreement obtained between calculated and measured observables.
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    URL: http://dx.doi.org/10.1023/A:1006943205351
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    Computational carbohydrate chemistry: what theoretical methods can tell us (1998)
    Springer
    Glycoconjugate journal 15 (1998), S. 209-216 
    Details
    ISSN: 1573-4986
    Keywords: conformational analysis ; molecular dynamics ; NMR ; free energy ; perturbation ; oligosaccharide ; polysaccharide ; GLYCAM
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Computational methods have had a long history of application to carbohydrate systems and their development in this regard is discussed. The conformational analysis of carbohydrates differs in several ways from that of other biomolecules. Many glycans appear to exhibit numerous conformations coexisting in solution at room temperature and a conformational analysis of a carbohydrate must address both spatial and temporal properties. When solution nuclear magnetic resonance data are used for comparison, the simulation must give rise to ensemble-averaged properties. In contrast, when comparing to experimental data obtained from crystal structures a simulation of a crystal lattice, rather than of an isolated molecule, is appropriate. Molecular dynamics simulations are well suited for such condensed phase modeling. Interactions between carbohydrates and other biological macromolecules are also amenable to computational approaches. Having obtained a three-dimensional structure of the receptor protein, it is possible to model with accuracy the conformation of the carbohydrate in the complex. An example of the application of free energy perturbation simulations to the prediction of carbohydrate-protein binding energies is presented.
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    URL: http://dx.doi.org/10.1023/A:1006984709892
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    Studies on the interactions between anionic surfactants and polyvinylpyrrolidone: Surface tension measurement, 13C NMR and ESR (1998)
    Springer
    Colloid & polymer science 276 (1998), S. 1-10 
    Details
    ISSN: 1435-1536
    Keywords: Key words Interaction ; anionic surfactant ; polyvinylpyrrolidone ; ESR ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  The interaction between anionic surfactants and polyvinylpyrrolidone (PVP) are investigated using 13C NMR, ESR spectroscopy and surface tension measurements at the air/water interface. The behavior of single-chained surfactant, sodium dodecyl sulphonate (AS), is compared with that of the double-chained surfactant, sodium bis(2-ethylhexyl) phosphate (NaDEHP). The results showed that a surfactant–polymer complex of “necklace and head structure” is formed in AS aqueous solutions in the presence of PVP due to the hydrophobic interaction between PVP and AS. The AS micelles nucleate on the polymer hydrophobic sites, and the mobility of the AS head groups is not affected. But, for NaDEHP surfactant, it was found that PVP is little effective in influencing the monomer–micelle equilibrium and no surfactant– polymer complex formed in the NaDEHP aqueous solution.
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    URL: http://dx.doi.org/10.1007/s003960050201
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    Conformational Studies of Tachykinin Peptides Using NMR Spectroscopy (1998)
    Springer
    International journal of peptide research and therapeutics 5 (1998), S. 429-432 
    Details
    ISSN: 1573-3904
    Keywords: conformation ; molecular modelling ; NMR ; scyliorhinins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A conformational analysis in water and DMSO of two tachykinin family peptides (scyliorhinin I (ScyI) and scyliorhinin II (ScyII)) was carried out by 1D and 2D NMR (DQF-COSY, TOCSY, HMQC, HMBC, NOESY and ROESY) and molecular dynamics calculation methods. In DMSO, two groups of conformations (major and minor) were obtained for both peptides based on the experimental data. The conformations proposed for ScyI represent a folded structure, which shows certain similarities to the structures reported for other NK-1 and NK-2 tachykinin agonists. In water ScyII displays a flexible, extended structure, whereas in DMSO the structure is more compact and, in the fragment from the centre to the C-terminus, several β-turns may be present.
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    NMR Studies of the MDP Conjugates with Amino-Acridine/Acridone Derivatives (1998)
    Springer
    International journal of peptide research and therapeutics 5 (1998), S. 409-412 
    Details
    ISSN: 1573-3904
    Keywords: amino-acridine ; amino-acridone ; anticancer activity ; MDP ; muramyl peptide ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract 1H and 13C NMR studies allowed us to determine the structure of anticancer active MDP analogs modified at the C-terminus with amino-acridine/acridone derivatives. The products contain an isoglutamine residue without contamination by their isomers containing a glutamine residue as could be expected based on the literature data.
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    URL: http://dx.doi.org/10.1023/A:1008878409340
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    Conformational studies of tachykinin peptides using NMR spectroscopy (1998)
    Springer
    International journal of peptide research and therapeutics 5 (1998), S. 429-432 
    Details
    ISSN: 1573-3904
    Keywords: conformation ; molecular modelling ; NMR ; scyliorhinins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A conformational analysis in water and DMSO of two tachykinin family peptides (scyliorhinin I (ScyI) and scyliorhinin II (ScyII)) was carried out by 1D and 2D NMR (DQF-COSY, TOCSY, HMQC, HMBC, NOESY and ROESY) and molecular dynamics calculation methods. In DMSO, two groups of conformations (major and minor) were obtained for both peptides based on the experimental data. The conformations proposed for ScyI represent a folded structure, which shows certain similarities to the structures reported for other NK-1 and NK-2 tachykinin agonists. In water ScyII displays a flexible, extended structure, whereas in DMSO the structure is more compact and, in the fragment from the centre to the C-terminus, several β-turns may be present.
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    Computer Modeling of the Solution Conformation of Cyclic Enkephalins (1998)
    Springer
    International journal of peptide research and therapeutics 5 (1998), S. 445-447 
    Details
    ISSN: 1573-3904
    Keywords: computer modeling ; conformation ; enkephalins ; fluorescence ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The probable conformations of two cyclic enkephalin analogs, DNS-cyclo[D-Dab-Gly-Trp-Leu] (I) and DNS-cyclo[D-Dab-Gly-Trp-D-Leu] (II) (DNS = dansyl), were determined by combining the results of NOE, vicinal coupling constant and fluorescence energy transfer measurements with theoretical calculations. The common feature of the conformations for both peptides is the presence of a β-turn at residues 2 and 3.
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    URL: http://dx.doi.org/10.1023/A:1008880613066
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    NMR studies of the MDP conjugates with amino-acridine/acridone derivatives (1998)
    Springer
    International journal of peptide research and therapeutics 5 (1998), S. 409-412 
    Details
    ISSN: 1573-3904
    Keywords: amino-acridine ; amino-acridone ; anticancer activity ; MDP ; muramyl peptide ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary 1H and13C NMR studies allowed us to determine the structure of anticancer active MDP analogs modified at the C-terminus with amino-acridine/acridone derivatives. The products contain an isoglutamine residue without contamination by their isomers containing a glutamine residue as could be expected based on the literature data.
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    URL: http://dx.doi.org/10.1007/BF02443496
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    Computer modeling of the solution conformation of cyclic enkephalins (1998)
    Springer
    International journal of peptide research and therapeutics 5 (1998), S. 445-447 
    Details
    ISSN: 1573-3904
    Keywords: computer modeling ; conformation ; enkephalins ; fluorescence ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The probable conformations of two cyclic enkephalin analogs, DNS-cyclo[d-Dab-Gly-Trp-Leu] (I) and DNS-cyclo[d-Dab-Gly-Trp-d-Leu] (II) (DNS=dansyl), were determined by combining the results of NOE, vicinal coupling constant and fluorescence energy transfer measurements with theoretical calculations. The common feature of the conformations for both peptides is the presence of a β-turn at residues 2 and 3.
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    Metabolism-independent binding of toxic metals by Ulva lactuca: cadmium binds to oxygen-containing groups, as determined by NMR (1997)
    Springer
    BioMetals 10 (1997), S. 105-117 
    Details
    ISSN: 1572-8773
    Keywords: BET ; biosorption ; cadmium ; cobalt ; copper ; Freundlich ; NMR ; Scatchard ; Ulva lactuca ; zinc
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The metabolism-independent metal binding characteristics of Ulva lactuca were investigated using both freeze-dried thalli and cell walls stripped of intracellular material by incubation in Triton-X followed by methanol. Biosorption of Cd, Zn, Cu and Co by freeze-dried thallus was concentration-dependent and followed Freundlich and Langmuir isotherms. The Freundlich plot suggested that freeze-dried U. lactuca had the greatest binding affinity for Cu compared with Cd, Zn and Co. The BET (Brunauer–Emmett–Teller) plot, which indicates a more complex form of adsorption, and the Scatchard plot were not adequate models for Cu adsorption. The Scatchard plot of Cd suggested that two Cd binding sites were available on the freeze-dried thallus, with the second, lower affinity site only becoming available at Cd loading capacities greater than 4.9mmol g dry wt. Cd nuclear magnetic resonance (NMR) studies confirmed that two binding sites were available for Cd on the freeze-dried algal powder, though only one was available on the cell wall, and that the affinity of the binding sites was greater for Cu than for Cd. The results of the NMR experiments suggested that Cd binds to oxygen-containing functional groups in the algal powder and on the cell wall. It is proposed that sulphate or hydroxyl groups attached to polysaccharide subunits are possible sites.
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    NMR analysis of cellulose dissolved in aqueous NaOH solutions (1997)
    Springer
    Cellulose 4 (1997), S. 99-107 
    Details
    ISSN: 1572-882X
    Keywords: sodium hydroxide ; mercerization ; NMR ; chemical shift
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Low molecular weight cellulose (degree of polymerization = ca 15) was dissolved in 4-- 30% NaOD/D2O, and relationships between 1H- and 13C-chemical shifts of the cellulose and NaOD concentrations were studied in terms of the dissociation of three hydroxyl groups of cellulose in aqueous NaOH solutions. All C---H proton resonances were shifted upfield linearly with an increase in the NaOD concentration, indicating that all C---H protons of cellulose undergo the electron-shielding effect by NaOH. On the other hand, the shifting patterns of carbon resonances varied among the six carbons: C1 and C4 carbons undergo the electron-shielding effect, whereas C2, C3, C5, and C6 carbons experience the electron-deshielding effect by NaOH. Changes in 13C-chemical shifts of cellulose carbons in 4--30% NaOD/D2O indicate that C3---OH has the highest resistance to dissociation in aqueous NaOH of the three hydroxyl groups of an anhydroglucose residue. It is plausible, at least from the aspects of 13C-chemical shifts, that cellulose molecules dissolving in 20--30% NaOH behave differently from those swollen in 20--30% NaOH as alkali- cellulose
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    URL: http://dx.doi.org/10.1023/A:1018471419692
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    Spin-lattice relaxation behaviour of water in cellulose materials in relation to the tablet forming ability of microcrystalline cellulose particles (1997)
    Springer
    Cellulose 4 (1997), S. 57-73 
    Details
    ISSN: 1572-882X
    Keywords: microcrystalline cellulose ; tablet ; water ; spin- lattice relaxation time ; spin-spin relaxation time ; NMR ; microfibril
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Medical tablet forming ability of microcrystalline cellulose (MCC) was investigated in relation to the mobility of water molecules in MCC particles. For this purpose, the spin-lattice relaxation time T1 of water in the system was measured by 1H-NMR. Over a wide range of water contents (0.02 ≤ H2O/cellulose (g/g) ≤ 1.79), two different T1 (T1,l and T1,s) values were observed for water in each MCC sample. Below the equilibrium water content, water having these two different T1 values exchange with each other in an MCC particle reaching an equilibrium state within a given time scale (equilibrium constant K). The T1,l, T1,s and K values for water in MCC, estimated at the equilibrium water content, showed fairly good correlations with the hardness of the tablets made by the MCC samples. Sample with a shorter T1, or larger K tended to have a stronger tablet forming ability. In the spin-spin relaxation time T2 measurements for protons in an MCC/D2O system, two T2 components originating from the glassy cellulose solid (T2,G) and the swelling region (T2,l) were observed. It was found that the mole fraction xL of protons with T2,L in the system exhibits a clear linear correlation with K. From these results, a structural model for the distribution of water in MCC particles was propoed by taking the surface of each microfibril and the disordered region within the microfibril into consideration
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    Chemie polyfunktioneller Moleküle, 126 Mitt. Synthese, Struktur und Tautomerie von 5-Fluor-N(1), N(3)-bis(diphenylphosphanyl)-uracil (1997)
    Springer
    Monatshefte für Chemie 128 (1997), S. 399-410 
    Details
    ISSN: 1434-4475
    Keywords: Diphenylphosphanyl substituted 5-fluoro-uracils ; X-ray structure determination ; Tautomerism ; NMR ; Vibrational and mass spectra
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary 5-Fluoro-uracil (1) reacts with chloro-diphenylphosphane to 5-fluoro-N(1), N(3)-bis(diphenylphosphanyl)uracil (3) which was characterized by X-ray crystallography, IR, and mass spectra.19F,31P{1H},13C{1H}, and1H NMR spectra indicate that3 rearranges inTHF solution to some extent to the tautomeric 5-fluoro-O(2), O(4)-bis(diphenylphosphanyl)uracil (4). If the solvent contains traces of water, Ph2P(O)-PPh2 (6) and uracil derivatives are formed by hydrolysis.
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    Radical reactions of N-heterocyclic compounds, XV. Radial intermediates and end products of the oxidation of 3-anilino-1,5-diphenylpyrazoles with Pb(OAc)4 (1997)
    Springer
    Monatshefte für Chemie 128 (1997), S. 261-270 
    Details
    ISSN: 1434-4475
    Keywords: Aminyl radicals ; ESR ; NMR ; Pyrazoles ; Triarylaminium cation radicals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die substituierten 3-Anilino-1,5-diphenylpyrazole1a–i wurden mit Pb(OAc)4 in Benzol oder CH2Cl2 oxidiert. Die intermediären Aminylradikale3f–i wurden ESR-spektroskopisch bei der Oxidation der im Anilinrest methylsubstituierten Pyrazole1f–i nachgewiesen. Die ESR-spektroskopisch nach Oxidation der Pyrazole1a–e beobachteten Radikalintermediate interpretieren wir als Kationradikale6a–e. Diese werden durch Weiteroxidation der Dimeren4a–e gebildet, deren Struktur durch NMR-Untersuchungen und15N-Markierung bewiesen wurde.
    Notes: Summary Substituted 3-anilino-1,5-diphenylpyrazoles1a–i were oxidized with Pb(OAc)4 in benzene or CH2Cl2 solution. The ESR measurements confirmed the formation of aminyl radicals3f–i frompara-CH3 substituted pyrazoles1f–i. The radical intermediates from unsubstituted pyrazoles1a–e were assigned to triarylaminium cation radicals These were generated by consecutive oxidation of the dimeric products4a–e whose structure was proven by NMR spectroscopy and15N labeling.
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    Phosphate uptake and polyphosphate metabolism of mycorrhizal and nonmycorrhizal roots of pine and of Suillus bovinus at varying external pH measured by in vivo 31P-NMR (1997)
    Springer
    Mycorrhiza 7 (1997), S. 101-106 
    Details
    ISSN: 1432-1890
    Keywords: Key words External pH ; NMR ; Phosphate ; Polyphosphate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Comparative in vivo 31P-NMR analyses of mycorrhizal and nonmycorrhizal roots of Pinus sylvestris and the fungus of Suillus bovinus in pure culture were used to investigate alterations in phosphate metabolism due to changes in external pH in the range 3.5–8.5. All control samples maintained a constant pH in both cytoplasm and vacuole. Mycorrhizal roots and pure fungus, but not nonmycorrhizal roots, transformed accumulated inorganic phosphate into mobile polyphosphate with a medium chain length. Phosphate uptake rates and polyphosphate accumulation responded differently to external pH. In all cases, maximal phosphate uptake occurred at an external pH close to 5.5. At an external pH of 8.5, both roots and fungus showed a distinct lag in phosphate uptake, which was abolished when the external pH was lowered to 7.5. An irreversible effect on phosphate uptake as a consequence of variation in external pH was also observed. The central role of the fungus in regulating mycorrhizal phosphate metabolism is discussed.
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    Molecular Dynamic and Conformational Study of an Unsaturated 12-crown-S2O2 Ether and its AgI Complexes (1997)
    Springer
    Journal of molecular modeling 3 (1997), S. 355-358 
    Details
    ISSN: 0948-5023
    Keywords: Keywords: Thiocrown ether ; NMR ; Ag(I) complexes ; Molecular Dynamic simulations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The preferred conformations and the complexional behaviour of mn-12S2O2 were studied by means of both NMR spectroscopy and molecular modelling. Furthermore, the AgI complexes of this ligand mn-12S2O2 were also studied by molecular mechanical calculations.
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    A1 H spin echo and 51V NMR study of the interaction of vanadate with intact erythrocytes (1997)
    Springer
    JBIC 2 (1997), S. 235-241 
    Details
    ISSN: 1432-1327
    Keywords: Key words Vanadium ; Erythrocyte ; NMR ; Oxidative stress ; Diabetes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  The action of vanadate on intact human erythrocytes was studied by 1H spin echo and 51V NMR spectroscopy as a model for the behaviour of vanadium(V) complexes in experimental diabetes. Vanadate is reduced by the intact erythrocyte at the expense of intracellular glutathione which rapidly depletes from the intracellular volume. Using the blocking agent 4,4′-diisothio-cyanatostilbene-2,2′-disulfonic acid (DIDS), which specifically blocks the anion transporter, vanadate reduction could be inhibited and glutathione depletion arrested. Thus, for the reaction with the intact cell to occur, vanadium(V) must cross the cell wall, possibly via the anion transporter. Nitrofurantoin was used to inhibit glutathione reductase in the erythrocyte suspensions. Under these conditions, treatment of the cells with vanadate induced glutathione oxidation prior to depletion. A study of the reaction of vanadate with haemolysate indicates that, without the influence of the membrane, rapid oxidation of glutathione to glutathione disulfide by the vanadyl cation occurs with no glutathione depletion, and that under these conditions vanadate reduction is incomplete. This study generates a model for the behaviour of vanadium complexes in vivo, providing a basis for the rational design and synthesis of new vanadium-based agents as insulin mimics. In essence, vanadium is transported across the membrane as vanadate(V), is reduced in situ by glutathione, and becomes complexed to a wide range of intracellular binding sites. Exchange reactions between glutathione and sulfhydryl groups present on haemoglobin and membrane lead to the depletion of glutathione from the cytosol.
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    Melittin-induced leakage from phosphatidylcholine vesicles is modulated by cholesterol: a property used for membrane targeting (1997)
    Springer
    European biophysics journal 25 (1997), S. 201-210 
    Details
    ISSN: 1432-1017
    Keywords: Key words Melittin ; Permeability ; Cholesterol ; Lipid-protein interaction ; Fluorescence ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Melittin, an amphiphathic peptide, affects the permeability of vesicles. This can be demonstrated using the dye release technique. Calcein, a fluorescent marker, is trapped in large unilamellar 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) vesicles and melittin-induced leakage of the dye can be monitored directly by increasing fluorescence intensity. First, we characterized the effect of increasing cholesterol content in the membrane on melittin-induced leakage and our results reveal that cholesterol inhibits the lytic activity of the peptide. Using intrinsic fluorescence of the single tryptophan of melittin and 2H-NMR of headgroup deuterated phosphatidylcholine, we demonstrated that the affinity of melittin for phosphatidylcholine vesicles is reduced in the presence of cholesterol; this is associated with the tighter lipid packing of the cholesterol-containing bilayer. This reduced binding is responsible for the reduced melittin-induced leakage from cholesterol-containing membranes. The pathway of release was determined to be an all-or-none mechanism. Finally, we investigated the possibility of achieving specific membrane targeting with melittin, when vesicles of different lipid composition are simultaneously present. Melittin incubated together with vesicles made of pure POPC and POPC containing 30(mol)% cholesterol can empty nearly all the cholesterol-free vesicles while the cholesterol-containing vesicles remain almost intact. Owing to the preferential interaction of melittin with the pure POPC vesicles, we were able to achieve controlled release of encapsulated material from a specific vesicle population.
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    Calcium binding and conformational properties of calmodulin complexed with peptides derived from myristoylated alanine-rich C kinase substrate (MARCKS) and MARCKS-related protein (MRP) (1997)
    Springer
    European biophysics journal 25 (1997), S. 239-247 
    Details
    ISSN: 1432-1017
    Keywords: Key words Calmodulin ; MARCKS ; Calcium binding ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The myristoylated alanine-rich C kinase substrate (MARCKS) and the MARCKS-related protein (MRP) are members of a distinct family of protein ki-nase C (PKC) substrates that bind calmodulin (CaM) in a manner regulated by Ca2+ and phosphorylation by PKC. The CaM binding region overlaps with the PKC phosphorylation sites, suggesting a potential coupling between Ca2+-CaM signalling and PKC-mediated phosphorylation cascades. We have studied Ca2+ binding of CaM complexed with CaM binding peptides from MARCKS and MRP using flow dialysis, NMR and circular dichroism (CD) spectroscopy. The wild-type MARCKS and MRP peptides induced significant increases in the Ca2+ affinity of CaM (pCa 6.1 and 5.8, respectively, compared to 5.2, for CaM in the absence of bound peptides), whereas a modified MARCKS peptide, in which the four serine residues susceptible to phosphorylation in the wild-type sequence have been replaced with aspartate residues to mimic phosphorylation, had smaller effect (pCa 5.6). These results are consistent with the notions that phosphorylation of MARCKS reduces its binding affinity for CaM and that the CaM binding affinity of the peptides is coupled to the Ca2+ affinity of CaM. All three MARCKS/MRP peptides perturbed the backbone NMR resonances of residues in both the N- and C-terminal domains of CaM and, in addition, the wild-type MARCKS and the MRP peptides induced strong positive cooperativity in Ca2+ binding by CaM, suggesting that the peptides interact with the amino- and carboxy-terminal domains of CaM simultaneously. NMR analysis of the Ca2+-CaM-MRP peptide complex, as well as CD measurements of Ca2+-CaM in the presence and absence of MARCKS/MRP peptides suggest that the peptide bound to CaM is non-helical, in contrast to the α-helical conformation found in the CaM binding regions of myosin light-chain kinase and CaM-dependent protein kinase II. The adaptation of the CaM molecule for binding the peptide requires disruption of its central helical linker between residues Lys-75 and Glu-82.
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    The effects of calcium ions on double helical forms of gramicidin (1997)
    Springer
    European biophysics journal 26 (1997), S. 299-306 
    Details
    ISSN: 1432-1017
    Keywords: Key words Ion binding ; Circular dichroism spectroscopy ; NMR ; Divalent cations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The effects of binding calcium ions to the double helical forms of gramicidin present in methanol solution were examined using circular dichroism (CD) and nuclear magnetic resonance (NMR) spectroscopies. It was found that calcium ions principally alter the relative composition of the equilibrium mixture of gramicidin conformers present in the solvent. In the absence of calcium, both parallel and antiparallel double helices are present. However, the addition of small amounts of Ca2+ shifts the equilibrium towards the left-handed parallel double helical form. This conformational change prevents monovalent cations (caesiums) from binding to the gramicidin double helix, and even converts the shorter, wider anti-parallel double helical form normally produced in the presence of caesium into the longer, narrower parallel double helical form. Furthermore, a temperature study showed that calcium ions tend to stabilize this form relative to the ion-free forms. The conformation of gramicidin is further changed, becoming a disordered structure, when the concentration of Ca2+ is raised. Thus, the binding of divalent calcium ions has a number of dramatic effects on the conformations of gramicidin present in solution.
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    URL: http://dx.doi.org/10.1007/s002490050084
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    Reevaluation of the redox and redox-Bohr cooperativity in tetrahaem Desulfovibrio vulgaris (Miyazaki F) cytochrome c 3 (1997)
    Springer
    JBIC 2 (1997), S. 343-349 
    Details
    ISSN: 1432-1327
    Keywords: Key words Cooperativity ; Cytochrome c3 ; NMR ; Paramagnetic ; Redox-Bohr
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  The thermodynamic model of five interacting charge centres (four haems and an ionisable centre), which was used in the characterisation of the thermodynamic properties of Desulfovibrio vulgaris (Hildenborough) cytochrome c 3 (c 3DvH), is now used to reevaluate the thermodynamic properties in Desulfovibrio vulgaris (Miyazaki F) cytochrome c 3 (c 3DvM) on the basis of published data (Park, J.-S., Ohmura, T., Kano, K., Sagara, T., Niki, K., Kyogoku, Y. and Akutsu, H. (1996) Biochim. Biophys. Acta 1293, 45–54). Contrary to the assertion of Park et al. (1996), the pH dependence of the proton chemical shifts of haem methyls in c 3DvM in several stages of oxidation is well described by the model, which involves both homotropic (e–/e–) and heterotropic (e–/H+) cooperativity. This shows that the pH dependence observed for c 3DvM is not significantly more complicated than that observed for c 3DvH. Since the parameters which we now obtain for c 3DvM are generated with the same model as those from c 3DvH, albeit using less precise data, it is possible to make a preliminary comparison of the thermodynamic properties of these two proteins and of their role in energy transduction. The extrinsic dipolar shifts generated for each methyl group by each of the four haems in c 3DvM are also determined. A novel method for approximating the magnetic susceptibility tensors is used: the orientations of the principal axes of the tensors have been shown to be closely related to the geometry of the axial ligands, which is available from the X-ray structure of c 3DvM, and the components of the tensors are extrapolated from EPR g values. The inclusion of the calculated haem extrinsic contributions clearly describes the pH dependence of the haem methyls in the core of the protein, close to other haems. This description is most remarkable in the case of the haem methyl 21CH3 II I, for which the "unusual pH dependence" commented on by Park et al. (1996) is easily explained using the thermodynamic parameters determined by our model together with the calculated extrinsic dipolar shifts, thus providing a test of the analysis.
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    URL: http://dx.doi.org/10.1007/s007750050141
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    Metal-binding and active-site structure of di-zinc Streptomyces griseus aminopeptidase (1997)
    Springer
    JBIC 2 (1997), S. 744-749 
    Details
    ISSN: 1432-1327
    Keywords: Key words Aminopeptidase ; Streptomyces ; Dinuclear ; NMR ; Co2+ ; Cu2+
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  Streptomyces griseus aminopeptidase has been characterized to have a dinuclear active site and to follow a dinuclear hydrolytic mechanism by means of activity assay, optical, and NMR spectroscopy. A sequential binding of Co2+ to the dinuclear sites in 20 mM Mes buffer at pH 6.1 has also been established. The results from these studies suggest that the two metal sites have a five-coordination sphere, with at least one coordinated His each. A di-Cu2+-substituted derivative of the enzyme has been prepared which exhibits a 1H NMR spectrum with sharp hyperfine-shifted signals, again indicating the presence of a dinuclear active site. This 1H NMR spectrum with sharp hyperfine-shifted features represents a first of its kind for a di-Cu2+ center in metalloproteins.
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    URL: http://dx.doi.org/10.1007/s007750050190
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    Characterization of cytochrome c 6 from the cyanobacterium Anabaena PCC 7119 (1997)
    Springer
    JBIC 2 (1997), S. 225-234 
    Details
    ISSN: 1432-1327
    Keywords: Key words Cytochrome c6 ; Anabaena PCC 7119 ; EPR ; NMR ; Redox-Bohr
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  A soluble monoheme c–type cytochrome c 6 has been isolated from the cyanobacterium Anabaena PCC 7119. It is a basic protein, with a molecular mass of 9.7 kDa, which accepts electrons from Anabaena ferredoxin in the ferredoxin-NADP+reductase-dependent NADPH cytochrome c reductase activity assay. The turnover of the reaction has an optimum pH at 7.5. Flavodoxin can also replace ferredoxin in this assay, but with only 20% efficiency. Plastocyanin from Anabaena PCC 7119, as well as the c 6 cytochromes from the green algae Chlorella fusca and Monoraphidium braunii are also shown to accept electrons from Anabaena ferredoxin. The reduction potential of cytochrome c 6 at pH 6.7 was determined to be 338 mV and is pH dependent, with pK a ox=8.4±0.1 and pK a red≈9.5. The ferric and ferrous cytochrome forms and their pH equilibria have been studied using visible, EPR and 1H-NMR spectroscopies. The amino acid sequence and the visible and NMR spectroscopic data indicate that the heme iron has a methionine-histidine axial coordination in the pH range 5–11. However, the EPR data for the ferricytochrome are complex and show that in this pH range five distinct forms are present. Between pH 5 and 9 the spectrum is dominated by two rhombic species, with g–values at 2.94, 2.29, 1.43 and at 2.84, 2.34, 1.56, which interconvert with a pK a of 8.4. The NMR data also show a main interconversion between two cytochrome forms at this pH, which coincides with that determined from the pH dependence of the reduction potential. Both these forms were associated with a methionine-histidine heme-iron coordination by correlation with the visible and NMR spectral data, although having crystal field parameters atypical for this type of coordination. Anabaena cytochrome c 6 is one more example of a heme protein for which the widely used crystal field analysis of the EPR data (truth diagram) fails to unequivocally determine the type of heme-iron ligation.
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    URL: http://dx.doi.org/10.1007/s007750050128
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    Thermal decomposition of the magnesium, zinc, lead and niobium chelates derived from 8-quinolinol (1997)
    Springer
    Journal of thermal analysis and calorimetry 50 (1997), S. 625-632 
    Details
    ISSN: 1572-8943
    Keywords: DSC ; NMR ; 8-quinolinol compounds ; TG-DTG ; stability ; thermal decomposition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Solid M-Ox compounds, whereM represents Mg(II), Zn(II), Pb(II) and NbO(III), and Ox is 8-quinolinol, have been prepared. Thermogravimetry, derivative thermogravimetry (TG, DTG), differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR) and infrared absorption spectra (IR) have been used to characterize and to study the thermal stability and thermal decomposition of these compounds.
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    URL: http://dx.doi.org/10.1007/BF01979034
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    Influence of vanadate on glycolysis, intracellular sodium, and pH in perfused rat hearts (1997)
    Springer
    Molecular and cellular biochemistry 170 (1997), S. 53-64 
    Details
    ISSN: 1573-4919
    Keywords: vanadate effects ; glycolysis ; intracellular sodium ; NMR ; perfused rat hearts ; ischemia-reperfusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Vanadium compounds have been shown to cause a variety of biological and metabolic effects including inhibition of certain enzymes, alteration of contractile function, and as an insulin like regulator of glucose metabolism. However, the influence of vanadium on metabolic and ionic changes in hearts remains to be understood. In this study we have examined the influence of vanadate on glucose metabolism and sodium transport in isolated perfused rat hearts. Hearts were perfused with 10 mM glucose and varying vanadate concentrations (0.7‐100 μM) while changes in high energy phosphates (ATP and phosphocreatine (PCr)), intracellular pH, and intracellular sodium were monitored using 31P and 23Na NMR spectroscopy. Tissue lactate, glycogen, and (Na+, K+)-ATPase activity were also measured using biochemical assays. Under baseline conditions, vanadate increased tissue glycogen levels two fold and reduced (Na+, K+)-ATPase activity. Significant decreases in ATP and PCr were observed in the presence of vanadate, with little change in intracellular pH. These changes under baseline conditions were less severe when the hearts were perfused with glucose, palmitate and b-hydroxybutyrate. During ischemia vanadate did not limit the rise in intracellular sodium, but slowed sodium recovery on reperfusion. The presence of vanadate during ischemia resulted in attenuation of acidosis, and reduced lactate accumulation. Reperfusion in the presence of vanadate resulted in a slower ATP recovery, while intracellular pH and PCr recovery was not affected. These results indicate that vanadate alters glucose utilization and (Na+, K+)-ATPase activity and thereby influences the response of the myocardium to an ischemic insult.
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    URL: http://dx.doi.org/10.1023/A:1006899932108
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    Conformational Analysis of the Thrombin Receptor Agonist Peptides SFLLR and SFLLR-NH2 by NMR: Evidence for a Cyclic Bioactive Conformation (1997)
    Springer
    The protein journal 16 (1997), S. 113-131 
    Details
    ISSN: 1573-4943
    Keywords: Thrombin receptor peptide ; NMR ; conformation ; bioactivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The conformational properties of the pentapeptide Ser-Phe-Leu-Leu-Arg (P5), a human thrombin receptor-derived sequence forming part of a tethered ligand which activates the thrombin receptor, and its more active amide derivative Ser-Phe-Leu-Leu-Arg-NH2 (P5-NH2), have been studied by proton NMR spectroscopy in dimethylsulfoxide. Measurements of nuclear Overhauser effects, performed using two-dimensional rotating frame nuclear Overhauser (ROESY) and one-dimensional nuclear Overhauser enhancement (NOE) spectroscopy, revealed that P5 exists mainly in an extended conformation. However, proton–proton 1D-NOEs between Phe CαH and Ser CαH, Leu3 CαH and Leu3 NH, and Leu4 CαH and Leu4 NH, as well as between the Ser and Arg sidechains, also implicated a minor conformer for P5 having a curved backbone and a near-cyclic structure. In contrast to P5, measurements of NOEs and ROEs for P5-NH2 revealed a more stabilized cyclic structure which may account for its higher biological potency. Thus strong interresidue sequential NH (i)–NH (i + 1) interactions, as well as C-terminal carboxamide to N-terminal side-chain interactions, i.e., Arg CONH2 to Phe ring and Arg CONH2 to Ser $$C_\alpha /C_{\beta \beta '} $$ , observed at lower levels of the ROESY spectrum, supported a curved backbone structure for SFLLR-NH2. Since the higher potaency P5-NH2 analogue adopts predominantly a cyclic structure, a cyclic bioactive conformation for thrombin receptor agonist peptides is suggested.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026342001226
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    Nmr Structural Characterization of Oligo-N-Substituted Glycine Lead Compounds from a Combinatorial Library (1997)
    Springer
    Molecular diversity 3 (1997), S. 1-15 
    Details
    ISSN: 1573-501X
    Keywords: combinatorial library ; hydrophobic collapse ; NMR ; n-substituted glycines ; structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Synthesis and screening of combinatorial librariesfor pharmaceutical lead discovery is a rapidlyexpanding field. Oligo-N-substituted glycines (NSGs)were one of the earliest sources of moleculardiversity in combinatorial libraries. In one of thefirst demonstrations of the power of combinatorialchemistry, two NSG trimers, CHIR-2279 and CHIR-4531,were identified as nM ligands for two 7-transmembraneG-protein-coupled receptors. The NMR characterizationof these two lead compounds was undertaken to verifycovalent connectivity and to determine solutionconformations, if any. The sequential chemical shiftassignments were performed using a new strategy forassigning 1H and 13C resonances of NSGs. The conformational preferences were then determined inboth an aqueous co-solvent system and an organicsolvent to probe the effects of hydrophobic collapse. NSGs are expected to be more flexible than peptidesdue to the tertiary amide, with both cis andtrans amide bond conformations being accessible. Solution NMR studies indicate that although CHIR-2279and CHIR-4531 have identical backbones and termini,and very similar side chains, they do not display thesame solution conformational characteristics.
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    URL: http://dx.doi.org/10.1023/A:1009698309407
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    Sequential Main-Chain Proton and Carbon Resonance Assignments for Wild-Type Yeast Iso-1 Ferrocytochrome c and Identification of Secondary Structural Elements (1997)
    Springer
    The protein journal 16 (1997), S. 775-786 
    Details
    ISSN: 1573-4943
    Keywords: Cytochrome c ; assignments ; ferrocytochrome c ; NMR ; 1H NMR ; 13C NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Yeast iso-1 cytochrome c is a naturally occurring protein that possesses an unusually reactive Cysl02 that imbues iso-1 with a complicated solution chemistry which includes spontaneous dimerization and poorly characterized redox reactions. For this reason previous studies of this typical member of the c-type cytochromes have been relegated to variant proteins in which the 102 position has been mutated, with most common changes involving serine and threonine. However, we have determined sequential 1H resonance assignments for the wild-type native protein because it is the actual participant in yeast mitochondrial electron transfer processes and because the wild-type native protein should be the fundamental assignment basis. In addition to 1H resonance assignments for 97 of 106 amino acids, we have also provided an extensive database of long-range NOEs. Comparison of these NOEs and a chemical shift index based upon α-H resonances has lead to identification of solution secondary structural elements that are consistent with the solid-state crystal structure. Although there is currently no efficient expression system that would facilitate isotope labeling of iso-1 cytochrome c, we tried to assess the usefulness of future heteronuclear experiments by using natural-abundance 1H/13C HMQC experiments to unambiguously assign 35 α-C resonances.
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    URL: http://dx.doi.org/10.1023/A:1026315900800
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    Carbohydrate-protein interaction studies by laser photo CIDNP NMR methods (1997)
    Springer
    Glycoconjugate journal 14 (1997), S. 531-534 
    Details
    ISSN: 1573-4986
    Keywords: Chemically induced dynamic nuclear polarization (CIDNP) ; carbohydrate-protein interaction ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The side chains of tyrosine, tryptophan and histidine are able to produce CIDNP (Chemically Induced Dynamic Nuclear Polarization) signals after laser irradiation in the presence of a suitable radical pair-generating dye. Elicitation of such a response in proteins implies surface accessibility of the respective groups to the light-absorbing dye. In principle, this technique allows the monitoring of the effect of ligand binding to a receptor and of site-directed mutagenesis on conformational aspects of any protein if CIDNP-reactive amino acids are involved. The application of this method in glycosciences can provide insights into the protein-carbohydrate interaction process, as illustrated in this initial model study for several N-acetyl-glucosamine-binding lectins of increasing structural complexity as well as for a wild type bacterial sialidase and its mutants. Experimentally, the shape and intensity of CIDNP signals are determined in the absence and in the presence of specific glycoligands. When the carbohydrate is bound, CIDNP signals of side chain protons of tyrosine, tryptophan or histidine residues can be broadened and of reduced intensity. This is the case for hevein, pseudo-hevein, the four hevein domains-containing lectin wheat germ agglutinin (WGA) and the cloned B-domain of WGA 1 (domB) representing one hevein domain. This response indicates either a spatial protection by the ligand or a ligand-induced positioning of formerly surface-exposed side chains into the protein’s interior part, thereby precluding interaction with the photo-activated dye. Some signals of protons from the reactive side chains can even disappear when the lectin-ligand complexes are monitored. The ligand binding, however, can apparently also induce a conformational change in a related lectin that causes the appearance of a new signal, as seen for Urtica dioica agglutinin (UDA) which consists of two hevein domains. Additionally, the three CIDNP-reactive amino acids are used as sensors for the detection of conformational changes caused by pH variations or by deliberate amino acid exchanges, as determined for the isolectins hevein and pseudo-hevein as well as for the cloned small sialidase of Clostridium perfringens and two of its mutants. Therefore, CIDNP has proven to be an excellent tool for protein-carbohydrate binding studies and can be established in glycosciences as a third biophysical method beside X-ray-crystallography and high-resolution multidimensional NMR studies which provides reliable information of certain structural aspects of carbohydrate-binding proteins in solution.
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    URL: http://dx.doi.org/10.1023/A:1018572023153
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    Effects of Ageing and Seeding on the Formation of Zeolite Y from Coal Fly Ash (1997)
    Springer
    Journal of porous materials 4 (1997), S. 245-251 
    Details
    ISSN: 1573-4854
    Keywords: fly ash ; zeolite Y ; ageing ; seeding ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Zeolite Y was selectively synthesised by treating Tarong fly ash in a hydrothermal system. The effects of ageing and seeding on the formation of the resultant phases, crystallisation kinetics, and gel chemistry of Si and Al were investigated. Most of the Si and Al components in the Tarong fly ash could be effectively transformed into zeolite Y in the presence of seeds but not the mineral phase, like mullite. The maximum crystallinity of zeolite Y obtained was 72%. The cation-exchange capacity (CEC) of the fly ash was 0.08 mmol/g but increased to 3.2 mmol/g after a proper treatment. Crystallisation of zeolite materials from fly ash is quite different from that of normal zeolite synthesis because the sources of Si and Al are relatively less reactive and other cation ions (e.g., K+, Mg2+) are present in fly ash. Zeolite P is a competitive phase present in the resulting products that could be eliminated by employing the seeding method. NMR study demonstrated that ageing plays an important role in enhancing the hydrothermal condition during which both Si and Al in fly ash dissolved into a basic solution and reacted to form ring-like structures, and further to zeolite materials. Seeding can selectively induce the formation of zeolite Y and eliminate the processes of induction and nucleation.
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    URL: http://dx.doi.org/10.1023/A:1009669104923
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    lonization and Solubilization of 4 Alkyl Benzole Acids and 4 Alkyl Anilines in Sodium Taurodeoxycholate Solutions (1997)
    Springer
    Pharmaceutical research 14 (1997), S. 1574-1582 
    Details
    ISSN: 1573-904X
    Keywords: ionization ; solubilization ; bile salts ; micelles ; NMR ; partition coefficient
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. The aqueous solubility and the extent of solubilization and ionization constant in sodium taurodeoxycholate (NaTDC) solutions of a series of benzoic acid and aniline derivatives were measured as a basis to characterize and thereby help predict the nature of the interaction of drugs with bile aggregates. Methods. The aqueous solubility and the solubilization of two series of compounds, 4-alkyl benzoic acids and 4-alkyl anilines, was measured as a function of NaTDC in 0 and 150 mM NaCl. The ionization constants were determined in water and in 50 mM NaTDC at sodium chloride concentrations of 0, 75 and 150 mM by spectrophotometric titration. The diffusion coefficients of NaTDC and the solutes were measured by pulsed-field gradient spin echo NMR spectroscopy. Results. The aqueous solubilities decreased with increasing alkyl chain length in both series, and the aniline derivatives had larger solubilities than the benzoic acid derivatives. The number of moles of solute solubilized per mole of bile salt ranged from 0.17 to 0.31 for the benzoic acid derivatives and from 1.3 to 3.0 for the aniline derivatives. The pKa values of the benzoic acid derivatives in the presence of NaTDC were higher relative to the controls, and the difference in the pKa (ΔpKa,obs) increased with increasing chain length. With the aniline derivatives, the pKa values were also shifted to higher values in NaTDC relative to the control but only in the absence of salt. The presence of the solute caused a decrease in the diffusion coefficient of NaTDC, and the diffusion coefficients of the solutes decreased with increasing alkyl chain length. With the hexyl derivatives, the diffusion coefficient of the solute was smaller than the diffusion coefficient of the bile salt. The chemical shift of the protons attached to carbon 18 and 19 of the bile salt were decreased to a greater extent in the presence of the solutes than the protons attached to carbon 26. Conclusions. Both the solubilization and ionization behavior of solutes were affected by the presence of bile salt aggregates. The surface potential and effective polarity of NaTDC aggregates were found to be dependent on the alkyl chain length for these two homologous series of solutes. The solubilization ratio was largely independent of alkyl chain length, but the unitary partition coefficient was dependent on both the alkyl chain length as well as ionization state. The derivatives reduced the diffusivity of the micelles suggesting the formation of larger sized aggregates and the solutes (hexyl derivatives) appear to favor association with the larger sized aggregates. The phenyl ring of the solutes appears to be oriented parallel to the plane of the steroid frame with preferential positioning near the hydrophobic rings.
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    URL: http://dx.doi.org/10.1023/A:1012178318128
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    Effect of Restricted Conformational Flexibility on the Permeation of Model Hexapeptides Across Caco-2 Cell Monolayers (1997)
    Springer
    Pharmaceutical research 14 (1997), S. 169-175 
    Details
    ISSN: 1573-904X
    Keywords: peptide delivery ; conformation ; Caco-2 cells ; membrane permeability ; NMR ; CD
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. To determine how restricted conformational flexibility of hexapeptides influences their cellular permeation characteristics. Methods. Linear (Ac-Trp-Ala-Gly-Gly-X-Ala-NH2; X = Asp, Asn, Lys) and cyclic (cyclo[Trp-Ala-Gly-Gly-X-Ala]; X = Asp, Asn, Lys) hexapeptides were synthesized, and their transport characteristics were assessed using the Caco-2 cell culture model. The lipophilicities of the hexapeptides were determined using an immobilized artificial membrane. Diffusion coefficients used to calculate molecular radii were determined by NMR. Two-dimensional NMR spectroscopy, circular dichroism, and molecular dynamic simulations were used to elucidate the most favorable solution structure of the cyclic Asp-containing peptide. Results. The cyclic hexapeptides used in this study were 2−3 times more able to permeate (e.g., Papp = 9.3 ± 0.3 × 10−8 cm/sec, X = Asp) the Caco-2 cell monolayer than were their linear analogs (e.g., Papp = 3.2 ± 0.3 × 10−8 cm/sec, X = Asp). In contrast to the linear hexapeptides, the flux of the cyclic hexapeptides was independent of charge. The cyclic hexapeptides were shown to be more lipophilic than the linear hexapeptides as determined by their retention times on an immobilized phospholipid column. Determination of molecular radii by two different techniques suggests little or no difference in size between the linear and cyclic hexapeptides. Spectroscopic data indicate that the Asp-containing linear hexapeptide exists in a dynamic equilibrium between random coil and β-turn structures while the cyclic Asp-containing hexapeptide exists in a well-defined compact amphophilic structure containing two β-turns. Conclusions. Cyclization of the linear hexapeptides increased their lipophilicities. The increased permeation characteristics of the cyclic hexapeptides as compared to their linear analogs appears to be due to an increase in their flux via the transcellular route because of these increased lipophilicities. Structural analyses of the cyclic Asp-containing hexapeptide suggest that its well-defined solution structure and, specifically the existence of two β-turns, explain its greater lipophilicity.
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    Isolation and Characterization of Major Phase I and II Metabolites of Ibuprofen (1997)
    Springer
    Pharmaceutical research 14 (1997), S. 676-680 
    Details
    ISSN: 1573-904X
    Keywords: ibuprofen ; metabolites ; NMR ; HPLC
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
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    URL: http://dx.doi.org/10.1023/A:1012125700497
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    Effects of hydroxy compounds on gel formation of gelatin (1997)
    Springer
    Colloid & polymer science 275 (1997), S. 67-72 
    Details
    ISSN: 1435-1536
    Keywords: Key words Gelatin ; gel formation ; NMR ; viscoelasticity ; circular dichroism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  Network formation of gelatin gel is known to consist of three-dimensionally cross-linked triple helices among polypeptide chains. The effects of added low molecular weight mono-ols, diols and polyols on the higher-order structure formation of gelatin chains were investigated using the following measurements: melting temperature, viscoelasticity and spin-lattice relaxation time (T 1) of H17 2O of gels, and circular dichroism spectra of diluted gelatin solutions. Furthermore, hydration behaviors of these hydroxy compounds were evaluated from the dynamic hydration numbers (n DHN) derived from T 1 of H17 2O in the solutions. It was found that network structures of gelatin gels containing hydoxy compounds were influenced by the number and position of hydroxyl groups as well as the number of carbon atoms of these coexisting compounds. The effect of hydroxyl groups of hydroxy compounds was considered to stabilize the helices among gelatin chains. Especially, the addition of polyols with large number of hydroxyl groups increased the number of cross-linking junctions in the gel networks, which consist of the aggregation among the helices. On the contrary, the effect of carbon atoms of hydroxy compounds is to disturb the formation of the helices and the aggregation among the helices.
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    URL: http://dx.doi.org/10.1007/s003960050053
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    Chemical transformation, phytotoxicity and nutrient availability in progressive composting stages of wheat straw (1997)
    Springer
    Plant and soil 196 (1997), S. 15-25 
    Details
    ISSN: 1573-5036
    Keywords: compost ; manure ; maturity ; NMR ; plant yield ; wheat straw
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Chemical maturity parameters in addition to plant growth limiting factors have been monitored in the course of a 2-month composting experiment. Wheat straw with 5% dry w horse manure was adjusted to C/N= 45 with urea. The pile was rotated and homogeneous samples were taken every four days. The most intense changes in straw fractions occurred in the first 20 days of composting, as suggested by wet chemical analyses, thermogravimetry and 13C NMR spectrometry. Nevertheless, plant response to compost application gave significant changes at between 20–60 days that were not clearly reflected by the above techniques. Glasshouse experiments with a soil treated with compost samples taken at the successive transformation stages suggested no linear correlation between composting time and the potential of compost in improving plant yield. In the samples taken after 20 days in the conditions studied, referred to as postmature composts, the ryegrass yield did not depend on most of the organic matter characteristics, but closely paralleled the concentration of available nitrogen and – to lesser extent – phosphorous in the compost. The probable immobilization of these elements in the course of composting was also suggested by plant response experiments with different doses of compost and the addition or not of mineral solution.
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    URL: http://dx.doi.org/10.1023/A:1004240927483
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    Rheo-NMR study of a non-flow-aligning side-chain liquid crystal polymer in nematic solution (1997)
    Springer
    Rheologica acta 36 (1997), S. 618-627 
    Details
    ISSN: 1435-1528
    Keywords: NMR ; viscometry ; shear flow ; liquid-crystalline polymer ; nematic solvent
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The flow behavior of a highly concentrated solution of a nematic side-chain liquid crystal polymer in a low molecular mass nematic solvent is investigated by deuterium nuclear magnetic resonance with simultaneous measurement of the shear viscosity in a cone-and-plate NMR viscometer. The director orientation under shear in the magnetic field is determined from the quadrupole splitting of the NMR spectra. The orientation as a function of shear rate is analyzed in terms of the Ericksen-Leslie-Parodi theory, yielding the Leslie coefficients μ 2 and μ 3 and thus the flow alignment parameter λ. From the combined analysis of orientation and viscosity as a function of shear rate a total of four independent viscosity parameters is obtained for the nematic solution. The value determined for the flow-alignment parameter, λ≈0.2, and the analysis of the data based on Brochard's theory show that the polymer is of the non-flow-aligning type and has a slightly prolate shape.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00367357
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  • 86
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    Scopolamine and atropineN-methyl diastereomer stability.Ab initio calculations onO-formylscopine andO-formyltropine model compounds (1997)
    Springer
    Structural chemistry 8 (1997), S. 319-329 
    Details
    ISSN: 1572-9001
    Keywords: Scopolamine ; atropine ; scopine ; tropine ; ab initio ; X-ray crystallography ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Ab initio geometry optimizations at the RHF-21G basis set level were calculated forequatorial andaxial N-methyl diastereomers ofO-formyltropine andO-formylscopine esters and other model compounds. These optimized geometries were then utilized as input for single-point energy calculations using the higher level RHF/6-31G* basis set to afford a more precise estimation of the total energies and atomic charges. Ethano bridge “pinching” of theN-protonated tropanyl piperidine moiety pushes the smalleraxial N-proton closer toward the neighboring twoaxial C-H bonds compared with the analogous case for a bulkyaxial N-methyl. Increasedcis 1,3-diaxial interactions in theaxial N-methyl diastereomer destabilize this epimer in favor of theequatorial N-methyl counterpart [e.g., 2.121 kcal/mol lower energy for theequatorial N-methylO-formyltropineN-protonated diastereomer (12) than for theaxial epimer (13)]. Lower pyramidality at nitrogen in the free base maintains the relative stability of theequatorial N-methyl free base diastereomer (14) (1.120 kcal/mol more stable than theaxial free base15). A nonprotonated carbon atom at the apex of a three-membered ring fused to the 6,7-positions of theO-formyltropine skeleton results in severe transannular nonbonding steric interactions involving the neighboringequatorial N-methyl group inN-protonated16 (3.335 kcal/mol less stable than theaxial N-methyl epimer17, where these transannular interactions are reduced due to the smallerequatorial N-H proton). Oxygen atom occupation of the apex of a similar fused three-membered ring retains the same severe transannular nonbonding steric interactions involving the neighboringequatorial N-methyl group inN-protonated18. These transannular interactions now become electrostatically attractive in theN-protonatedaxial N-methyl epimer19 (2.031 kcal/mol more stable than theequatorial epimer). Reduced pyramidality at nitrogen in theO-formylscopine free base reduces the repulsive transannular interaction with the neighboringequatorial N-methyl group compared to that in theN-protonated form. Lowered pyramidality also reduces thecis-1,3-diaxial interactions in theaxial N-methyl epimer, but the nitrogen lone pair is pushed close to the transannular oxygen lone pair as a result (theequatorial N-methyl free base20 is 3.870 kcal/mol more stable than theaxial epimer21). Theseab initio-calculated models ofO-formyltropines andO-formylscopineN-methyl diastereomeric protonated cations and free bases provide stereochemical insight into the relative stabilities of solution-state atropine and scopolamineN-methyl species previously observed by NMR spectroscopic methods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02281245
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    Restricted rotation about partial C,N double bonds (1997)
    Springer
    Structural chemistry 8 (1997), S. 217-226 
    Details
    ISSN: 1572-9001
    Keywords: NMR ; ab initio calculation ; restricted rotation ; solvent effects ; NBO
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The restricted rotation about the partial C,N double bond in 2-chloro-6-NR2-pyran-4-ones is discussed in the light of NMR spectroscopic data and theoretical calculations.Ab initio calculations at the HF/6-31G* level were carried out using a continuum model to take solvent effects into account. The delocalization ofπ-electron density [described by natural bond orbital analysis (NBO)] was applied to determine the degree of conjugation in the ground state (GS) and in the transition state (TS) for the restricted rotation of the compounds studied. The reason for the different barriers to rotation of the NR2 substituents (pyrrolidino 〉 dimethylamino 〉 morpholidino 〉 piperidino) at the 2-chloro-pyran-4-one ring appears to be the different steric hindrance of the NR2 substituents in the GS for the restricted rotation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02263510
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    Environmental variability in the reactivity of freshwater dissolved organic carbon to UV-B (1997)
    Springer
    Biogeochemistry 36 (1997), S. 89-97 
    Details
    ISSN: 1573-515X
    Keywords: dissolved organic carbon ; UV-B ; NMR ; lakes ; rivers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Reductions in the global stratospheric ozone layer arethought to be increasing the amount of ultraviolet B (UV-B) radiationreaching the planet’s surface and may be affecting the chemistry ofdissolved organic carbon (DOC) in surface waters. We studied theabundance of chromophores in DOC collected in four different aquaticenvironments in southwestern Nova Scotia using 13C nuclearmagnetic resonance (13C NMR) spectroscopy. We showed a clearseasonal pattern in the distribution of structural carbon related tolight-sensitive chromophores. There seemed to be little variation in theUV-B related chemical structure of DOC between lakes and streams, thoughwater from a bog pool showed large differences from the other samples. Thesepatterns of potential UV-B reactivity tend to be dampened however, byvariations in DOC concentrations which also occur seasonally.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005735929568
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  • 89
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    Surface Tension and 1H NMR Studies on Inclusion Complexes of β-Cyclodextrin with Sodium Alkyl Sulfonate (1997)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 28 (1997), S. 213-221 
    Details
    ISSN: 1573-1111
    Keywords: β-Cyclodextrin ; surfactants ; inclusion complexes ; NMR ; surface tension
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The inclusion complexes of β-CD with sodium octylsulfonate (C8As), sodium dodecyl sulfonate (C12As), andsodium hexadecyl sulfonate (C16As) in aqueous solutions havebeen studied by surface tension measurement at the air/water interfaceand 1H NMR spectroscopy at 323 K. At fixed concentrations of the surfactants, the surface tensions firstincrease with the increase of β-CD concentrations,then they attain a maximum. The surface tension curves of the surfactantsin the presence of β-CD are higher than those in the absence ofβ-CD. The values increase with increasing β-CD concentrations foreach surfactant. The apparent critical micelle concentrations (CMC) of thesurfactants vary linearly with β-CD concentrations. A 1H NMR study shows that the signals of theinner H-3 and H-5 of β-CDshift upfield upon addition of the surfactants.The magnitude of the chemicalshift changes (Δδ=δ CDδ obs)varies as a functionof the concentrations of the surfactants. From therelationships between the chemicalshift changes of H-3 or H-5 inside the β-CD cavityand guest/host molar ratios, a 1:1 stoichiometry foreach inclusion complex is assumed. The associationconstants of the inclusion complexes have beendetermined by 1H NMR spectroscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007923723044
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    Pentachlorophenol biodegradation by Pseudomonas spp. UG25 and UG30 (1997)
    Springer
    World journal of microbiology and biotechnology 13 (1997), S. 305-313 
    Details
    ISSN: 1573-0972
    Keywords: NMR ; pcpB ; pcpC ; pentachlorophenol degradation ; Pseudomonas spp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Eighty-nine bacterial isolates obtained by enrichment from pentachlorophenol (PCP)-contaminated soil samples were tested for PCP dechlorination activity and hybridization to pcpB (encoding PCP-4-monooxygenase) and pcpC (encoding tetrachlorohydroquinone reductive dehalogenase) gene probes synthesized by polymerase chain reaction from Flavobacterium sp. ATCC 39723 genomic DNA. Seven isolates were able to dechlorinate PCP, hybridize to both pcpB and pcpC DNA probes, and mineralize sodium pentachlorophenate (NaPCP) at an initial concentration of 100μg/ml. Although the seven PCP-mineralizing isolates possessed DNA sequences homologous to the Flavobacterium pcpB and pcpC genes, restriction analysis revealed sequence differences between the isolates and the Flavobacterium PCP dechlorination genes. Two isolates, designated UG25 and UG30, with the fastest onset and highest extent of PCP mineralization were selected for further study. Both isolates were tentatively identified as Pseudomonas spp. and exhibited stoichiometric release of Cl− ions as PCP was degraded. The release of Cl− began concomitantly with PCP disappearance from the medium. Both UG25 and UG30 degraded NaPCP at a concentration of 250 μg/ml in a minimal salt medium. Supplementation of the medium with glutamate increased the NaPCP degradation threshold of UG25 to a concentration of 300 μg/ml but did not affect that of UG30. 31P-NMR spectra of UG25 and UG30 cell suspensions exposed to PCP showed lower intracellular ATP levels and a more acidic cytoplasmic pH relative to untreated cells. This de-energization may explain the lack of cell growth in the presence of high PCP concentrations.
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    URL: http://dx.doi.org/10.1023/A:1018587108422
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    Spectroscopic Study of the Complexation of DDQ with 1,10-Diaza-18-crown-6 in Chloroform Solution (1997)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 28 (1997), S. 39-49 
    Details
    ISSN: 1573-1111
    Keywords: Diaza-18-crown-6 ; DDQ ; charge transfer complexes ; spectrophotometry ; IR ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The formation of charge transfer complexes with 1:1 and 2:1 stoichiometries (acceptor-to-donor) between DDQ and 1,10-diaza-18-crown-6 in chloroform solution was investigated spectrophotometrically. The stepwise formation constants of the resulting complexes were evaluated from the non-linear least-squaresfitting of the absorbance-mole ratio data. The enthalpies and entropiesof the complexation reactions were determined from the temperature dependence of the stepwise formation constants. The resulting 1:1 and 2:1 complexes were isolated in crystalline form and characterized. The results are consistent with the ionic structure of the resulting charge transfer complexes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007933827603
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    Chemical Surface Coating: Synthesis and Characterization of a Silicon Oxynitride Coated Silica Sel (1997)
    Springer
    Interface science 5 (1997), S. 95-101 
    Details
    ISSN: 1573-2746
    Keywords: silica gel ; surface modification ; silicon oxynitride ; FTIR ; XPS ; NMR ; porosity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Mesoporous silica gel has been coated with a thin silicon oxynitridefilm via chemical surface coating. In the first part of the synthesis, achemically bound preceramic polysilazane coating is formed layer by layer onthe pore walls at low temperature, using SiCl4 andNH3 as reagents. In the second part of the synthesis, thepolysilazane coated silica gel is pyrolysed, yielding a chemically bound,thin oxynitride coating. During the synthesis, the evolution of the chemical and morphologicalcomposition has been investigated with several elemental and spectroscopicanalysis techniques as well as with nitrogen porosimetry.
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    URL: http://dx.doi.org/10.1023/A:1008692707123
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    Micro-environment effect on the structure of synthetic substrates of thermolysin (1997)
    Springer
    International journal of peptide research and therapeutics 4 (1997), S. 391-395 
    Details
    ISSN: 1573-3904
    Keywords: Molecular modeling ; NMR ; Peptides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The conformations of thermolysin synthetic substrates in H2O/D2O (9/1) and glycerol-d 5 (5 M) are investigated using two-dimensional nuclear magnetic resonance spectroscopy and molecular modeling. The structures obtained from molecular modeling and NMR studies are compared. Comparisons of these structures with bound inhibitor in the active site of thermolysin are also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02442905
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    Structural modifications of oxidized insulin B-chain induced by glycerol addition (1997)
    Springer
    International journal of peptide research and therapeutics 4 (1997), S. 489-495 
    Details
    ISSN: 1573-3904
    Keywords: CD ; Endopeptidase ; Micro-environment ; NMR ; Subtilisin BPN′
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary 1H-NMR studies of the bovine insulin S-sulfonated B-chain are reported in H2O/D2O (9/1) and in glycerol-d 5 (5 M) using two-dimensional NMR spectroscopy. The first results show that the oxidized insulin B-chain secondary structure differs from that of native insulin by a loss of the α-helix between the two disulfide bridges and that the glycerol favours the structuring of the peptide.
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    URL: http://dx.doi.org/10.1007/BF02442922
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    Structural modifications of oxidized insulin B-chain induced by glycerol addition (1997)
    Springer
    International journal of peptide research and therapeutics 4 (1997), S. 489-495 
    Details
    ISSN: 1573-3904
    Keywords: CD ; Endopeptidase ; Micro-environment ; NMR ; Subtilisin BPN′
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract H-NMR studies of the bovine insulin S-sulfonatedB-chain are reported in H2O/D2O (9/1) and inglycerol-d5 (5 M) using two-dimensional NMRspectroscopy. The first results show that the oxidizedinsulin B-chain secondary structure differs from thatof native insulin by a loss of the α-helixbetween the two disulfide bridges and that theglycerol favours the structuring of the peptide.
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    URL: http://dx.doi.org/10.1023/A:1008822230053
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    Micro-environment effect on the structure of synthetic substrates of thermolysin (1997)
    Springer
    International journal of peptide research and therapeutics 4 (1997), S. 391-395 
    Details
    ISSN: 1573-3904
    Keywords: Molecular modeling ; NMR ; Peptides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The conformations of thermolysin synthetic substrates inH2O/D2O (9/1) and glycerol-d5 (5 M) are investigated using two-dimensional nuclearmagnetic resonance spectroscopy and molecular modeling. The structuresobtained from molecular modeling and NMR studies are compared. Comparisonsof these structures with bound inhibitor in the active site of thermolysinare also discussed.
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    URL: http://dx.doi.org/10.1023/A:1008881812479
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    Conformational study of a native monodisulfide bridge analogue of EETI II (1997)
    Springer
    International journal of peptide research and therapeutics 4 (1997), S. 245-249 
    Details
    ISSN: 1573-3904
    Keywords: Folding ; Molecular modelling ; NMR ; Squash trypsin inhibitor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Trypsin inhibitor EETI II, possessing six cysteinesengaged in three disulfide bridges, shares a commonstructural motif with other proteins of differentorigins and functions. To understand the principlesthat govern folding of this largely distributed basicscaffold, mainly composed of a small triple-strandedΒ-sheet, we have studied different stages in thefolding of EETI II. The conformational properties ofa synthetic analogue of EETI II possessing only onenative (15-27) disulfide bridge were investigated withthe combined use of 1H NMR and molecularmodelling. Although two native-like reverse turns wereobserved, formation of Β-sheet could not beevidenced in the one disulfide analogue, while themotif has been shown to be present in a foldingintermediate with two native disulfide bridges (9-21and 15-27). These results suggest that the structuralmotif requires stabilisation by two disulfide bridges
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    URL: http://dx.doi.org/10.1023/A:1008816030709
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    Temperature coefficients of peptides dissolved in hexafluoroisopropanol monitor distortions of helices (1997)
    Springer
    International journal of peptide research and therapeutics 4 (1997), S. 29-39 
    Details
    ISSN: 1573-3904
    Keywords: NMR ; Hydrogen bond ; Conformational shifts ; TFE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Temperature coefficients are widely used as an indication of solvent accessibility to amide protons. Low temperature coefficients are related to low accessibility and are often interpreted as evidence for intramolecular hydrogen bonding. Conformational shifts, i.e. the difference between chemical shifts of a particular residue in a structured and in a random-coil conformation, provide information on secondary structure. In particular, negative CHα conformational shifts are often used to delineate the extent of helical stretches. NH conformational shifts show large oscillations within a helix that have been interpreted as the result of helix distortions affecting hydrogen bond lengths. In the ocurse of the study of differnet peptides that adopt a helical structure in the presence of the structure-inducing solvent hexafluoroisopropanol (HFIP), we have found a strong correlation between temperature coefficients and amide conformational shifts. However, contrary to the initial expectations, lower temperature coefficients were associated to amide protons involved in longer, and presumably weaker, hydrogen bonds. The correlation can be explained, however, assuming that, in helical peptides dissolved in HFIP, temperature affects the chemical shift of amide protons mainly by changing the average length of intramolecular hydrogen bonds and changes in solvent accessibility play only a secondary role under these experimental conditions. The pattern of temperature coefficients in helical peptides can therefore be used to identify short or long hydragen bonds causing bending of the helix axis.
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    URL: http://dx.doi.org/10.1007/BF02443552
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    Temperature coefficients of peptides dissolved in hexafluoroisopropanol monitor distortions of helices (1997)
    Springer
    International journal of peptide research and therapeutics 4 (1997), S. 29-39 
    Details
    ISSN: 1573-3904
    Keywords: NMR ; Hydrogen bond ; Conformational shifts ; TFE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Temperature coefficients are widely used as an indication of solvent accessibility to amide protons. Low temperature coefficients are related to low accessibility and are often interpreted as evidence for intramolecular hydrogen bonding. Conformational shifts, i.e. the difference between chemical shifts of a particular residue in a structured and in a random-coil conformation, provide information on secondary structure. In particular, negative CHα conformational shifts are often used to delineate the extent of helical stretches. NH conformational shifts show large oscillations within a helix that have been interpreted as the result of helix distortions affecting hydrogen bond lengths. In the course of the study of different peptides that adopt a helical structure in the presence of the structure-inducing solvent hexafluoroisopropanol (HFIP), we have found a strong correlation between temperature coefficients and amide conformational shifts. However, contrary to the initial expectations, lower temperature coefficients were associated to amide protons involved in longer, and presumably weaker, hydrogen bonds. The correlation can be explained, however, assuming that, in helical peptides dissolved in HFIP, temperature affects the chemical shift of amide protons mainly by changing the average length of intramolecular hydrogen bonds and changes in solvent accessibility play only a secondary role under these experimental conditions. The pattern of temperature coefficients in helical peptides can therefore be used to identify short or long hydrogen bonds causing bending of the helix axis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008873632394
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  • 100
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    Conformational study of a native monodisulfide bridge analogue of EETI II (1997)
    Springer
    International journal of peptide research and therapeutics 4 (1997), S. 245-249 
    Details
    ISSN: 1573-3904
    Keywords: Folding ; Molecular modelling ; NMR ; Squash trypsin inhibitor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Trypsin inhibitor EETI II, possessing six cysteines engaged in three disulfide bridges, shares a common structural motif with other proteins of different origins and functions. To understand the principles that govern folding of this largely distributed basic scaffold, mainly composed of a small triple-stranded β-sheet, we have studied different stages in the folding of EETI II. The conformational properties of a synthetic analogue of EETI II possessing only one native (15–27) disulfide bridge were investigated with the combined use of1H NMR and molecular modelling. Although two native-like reverse turns were observed, formation of β-sheet could not be evidenced in the one disulfide analogue, while the motif has been shown to be present in a folding intermediate with two native disulfide bridges (9–21 and 15–27). These results suggest that the structural motif requires stabilisation by two disulfide bridges.
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    URL: http://dx.doi.org/10.1007/BF02442884
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