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  • 1
    Electronic Resource
    Electronic Resource
    Effect of spectral window size on circular dichroism spectra deconvolution of proteins
    Amsterdam : Elsevier
    Biophysical Chemistry 48 (1993), S. 19-29 
    Details
    ISSN: 0301-4622
    Keywords: Circular dichroism ; Deconvolution ; Proteins ; Spectral window size
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0301-4622(93)80038-K
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  • 2
    Electronic Resource
    Electronic Resource
    Changes induced in the surface characteristics and catalytic activity of amorphous Cu-Zr by hydrogen pretreatmentPart 4 of the series ‘Amorphous Alloy Catalysis’. For Part 3, see Ref. 14. (1992)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 19 (1992), S. 519-523 
    Details
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Hydrogen-treated amorphous Cu61Zr39 alloy ribbon exhibits the development of characteristic formations (hemispheres) in a circular arrangement (as revealed by SEM) on both sides of the ribbon, in parallel with copper enrichment (determined by AES) and partial crystallization (determined by differential scanning calorimetry). The extrusion of pure copper is considered to be caused by hydrogen diffusing into the bulk through existing surface defects. As a consequence of the surface and structural changes, steady increases in both the copper surface area and the catalytic activity (dehydrogenation of alcohols and isomerization of allyl alcohol and 2-propyloxirane) are demonstrated.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/sia.740190196
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  • 3
    Electronic Resource
    Electronic Resource
    Cooperativity of carbohydrate moiety orientation and β- turn stability is determined by intramolecular hydrogen bonds in protected glycopeptide modelsThis is publication No. 1708 from the Graduate Department of Biochemistry, Brandeis University, Waltham, Massachusetts, 02254-9110 (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 1549-1564 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 2, 3, 4, 6-Tetra-O-acetyl-β-D-gluco-, and β-D-galactopyranosides, as well as approximately 4 : 1 anomeric mixtures of α- and β-mannopyranosides of Boc-X-Y-NHCH3 dipeptides (X-Y = Pro-Ser, Pro-D-Ser, Val-Ser, Val-D-Ser, and Gly-Ser) have been synthesized. CD and ir spectroscopic studies were performed to characterize the conformation of the glycosylated peptide backbone and examine the possible formation of intrapeptide and glycopeptide intramolecular H-bonds. It was found that O-glycosylated peptides containing a D-serine residue are likely to adopt a type II β-turn while those with the Pro-Ser or Val-Ser sequence feature a type I(III) β-turn in solution. Glycosylation also increases the magnitude of the CD bands, characteristic of the given type of β-turns, which can be interpreted as an indication of the stablization of the folded backbone conformation. Infrared data showed that in nonpolar solutions the peracetyl glycopeptides adopt both single- and double H-bonded conformations whose ratio, in some cases, depends on the position at C-2′ of the H-bond acceptor acetoxy group. These data suggest that five-, seven-, or ten-membered glyco-turns may play an important role in fixing the steric orientation of the carbohydrate antennae systems in glycoproteins.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360291206
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  • 4
    Electronic Resource
    Electronic Resource
    Environment-dependent conformation of Boc-Pro-Ser-NHCH3 (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 763-771 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformation of Boc-Pro-Ser-NHCH3 (1) was studied in the solid state and in solution. In the crystal, the steric structure of 1 is characterized by an E(cis) urethane tertiary amide bond and the lack of intramolecular H bonds. Four-hundred megahertz 1H- and 101-MHz 13C-nmr studies in CDCl3 clearly show the presence of two conformers differing in the rotameric state of the tertiary-amide bond. Selective 1H-13C nuclear Overhauser enhancement experiments at -20°C as well as 1H-nmr and ir data indicate that the major trans conformer (84% in CDC13) may adopt a type I β-turn conformation with a possible Oγ - H-N interaction, similarly to Piv-Pro-Ser HCH3 (2) [A. Aubry, N. Ghermani, and M. Mar-raud (1984) Int. J. Peptide Protein Res. 23, 113-122]. Molecular mechanics calculations on the cis rotamer show that the β-pleated-like backbone conformation of serine in the crystal of 1 is not a low-energy state for the isolated molecule; it is caused by packing forces, particularly by the helical network of intermolecular H bonds.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360300711
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  • 5
    Electronic Resource
    Electronic Resource
    Characterization of β-turns in cyclic hexapeptides in solution by fourier transform IR spectroscopy (1993)
    New York : Wiley-Blackwell
    Biopolymers 33 (1993), S. 201-207 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The β-turn represents a structural element frequently encountered in globular proteins. However, in spite of various theoretical and experimental studies the ir signature bands of pure β-turns are still not established beyond doubt. Although considerable information exists now on the ir spectra of β-helical and β-sheet structures, the lack of knowledge concerning turn structures in general, and that of β-turns in particular, presents a major uncertainty in the estimation of global protein secondary structures from ir spectroscopic data. To obtain more specific information about the characteristic amide bands in β-turns, we report herein an ir spectroscopic analysis of a series of five cyclic pseudo-hexapeptides known to form β-turns from previous CD and nmr studies [A. Perczel, M. Hollósi, B. M. Foxman, and G. D. Fasman (1991) Journal of the American Chemical Society, Volume 113, pp. 9772-9784 ]. We show here that in these cyclic peptides the amide groups involved in β-turns that comprise a ten-membered hydrogen-bonded ring (and represent the first H-bond pair in a β-sheet), give rise to characteristic amide I bands in the range 1638-1646 cm-1, with the exact position depending on the solvent and the nature of the side-chain substituents. © 1993 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360330202
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  • 6
    Electronic Resource
    Electronic Resource
    Ca2+-induced conformational transitions of phosphorylated peptides (1993)
    New York : Wiley-Blackwell
    Biopolymers 33 (1993), S. 497-510 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: CD spectroscopic studies on protected peptides containing lysine and serine, or phosphoserine, and on serine-containing fragments of the neurofilament protein midsized subunit, both in the unphosphorylated and phosphorylated form, are reported. The introduction of the phosphoryl group was not found to have a significant spectral effect in aqueous solution. In trifluoroethanol (TFE), spectral shifts toward unordered (type U) spectra or the appearance of distorted spectra likely reflect the adoption of aperiodic polypeptide conformations due to salt bridge(s) between negatively charged phosphoserine and positive lysine side-chain groups. A turn-stabilizing effect of phosphorylation was also observed.CD-monitored titration experiments in TFE revealed a high conformational sensitivity of phosphopeptides toward Ca2+ ions. The appearance of the unordered spectra or spectral shifts were the sign of a bulk disordering effect of Ca2+ ions. Spectra with specific spectroscopic features reflect the formation of Ca2+complexes and the adoption of ordered unique backbone conformations.When ordered structures were obtained on addition of Ca2+ ions, the observed CD curves showed a resemblance to the spectrum of β-pleated sheets. This may originate from chain extension and the formation of β-pleated sheet segments fixed by Ca2+ bridges between PO3H1- groups of adjacent peptide chains. The data clearly show that the effect of the Ca2+ ions is highly specific: the sequence, chain length, presence and distribution of charged side-chain groups, degree and site of phosphorylation, and environmental factors appear to be determining in the process of chain extension or β-sheet formation. © 1993 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360330316
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  • 7
    Electronic Resource
    Electronic Resource
    Synthesis and conformational analysis of N-glycopeptides. II. CD, molecular dynamics, and nmr spectroscopic studies on linear N-glycopeptidesAbbreviations for dipeptides. Boc-Pro-Asn (Ac3GlcNHAc)-NHCH3: N4-3,4,6-tri-O-acetyl-2-acetamido-2-deoxy-β-D-glucopyranosyl-N2 - (tert-butyloxycarbonyl-L-prolyl) - asparagine-N-methylamide; Boc-Pro-Asn (GlcNHAc)-NHCH3: N4 - 2-acet-amido-2-deoxy-β-D-glucopyranosyl-N2 - (tert-butyloxycarbonyl L - prolyl) - asparagine - N - methylamide; Boc - Val - Asn (Ac-GlcNHAc) - NHCH3: N4-3,4,6-tri-O-acetyl-2-acetamido-2-deoxy-β-D-glucopyranosyl-N2 - (tert-butyloxycarbonyl-L-valyl) - aspar-agine-N-methylamide; Boc-Val-Asn (GlcNHAc) - NHCH3: N4 - 2-acetamido-2-deoxy-β-D-glucopyranosyl-N2 - (tert-butyloxycarbonyl-L-valyl) - asparagine-N-methylamide; Boc-Pro-Gln - (Ac3-GIcNHAc) - NHCH3: N5-3,4,6-tri-O-acetyl-2-acetamido-2-deoxy-β-D-glucopyranosyl-N2 - (tert -butyloxycarbonyl-L-prolyl) - gluta-mine-N′-methylamide; Boc-Pro-Gln (GlcNHAc)-NHCH3: N5-(2-acetamido -2-deoxy-β-D-glucopyranosyl)-N2- (tert-butyloxycar-bonyl -L-vrolyl) - glutamine - N-methylamide; Boc-Val Gln (GlcNHAc) -NHCH3: N5-3,4,6-tri-O-acetyl-2-acetamido-2-deoxy-β- D -glucopyranosyl-N2- (tertbutyloxycarbcnyl-L-valyl) - glutamine-N-methylamide; Boc-Val-Gln (GlcNHAc) - NHCH3: N5 - (2-acetamido-2-deoxy-β-D-glucopyranosyl)-N2 - (tert-butyloxycarbonyl-L-valy)-glutamine-N-methylamid; Ac3-NHAc-GlcNHAc: N-acetyl-3,4,6-tri-O-acetyl-2-acetaraido-2-deoxy-β-D-glucopyranosylamine; NHAcGlcNHAc: N-acetyl-2-acetamido-2-deoxy-β-D-glucopyranosylamine. (1993)
    New York : Wiley-Blackwell
    Biopolymers 33 (1993), S. 665-685 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The comprehensive structural analysis reported herein of eight N-glycopeptides, in three different solvents, is based on quantitative CD experiments, homonuclear nuclear Overhauser effect measurements, and molecular dynamics (MD) calculations. Although several orientations of the two amide planes attached to the carbohydrate pyranose ring are possible, according to NOE, CD data, and MD simulations, of all of the glycopeptide models, regardless of the type of the carrier peptide, only one dominant conformer population was found. This conformer is characterized by a nearly trans orientation of the CH and NH hydrogens of both acetamido groups. This finding is in perfect agreement with x-ray crystallographic data on the solid state conformation of the 1-N-acetyl- and 1-N-(β-aspartoyl)-2-acetamido-2-deoxy-β-D-glucopyranosylamine. The precise identification of this dominant conformer of N-glycopeptides in solution was the major question addressed herein by the structural analyses. A “CD additivity” experiment was carried out using an equimolar solution of Boc-Pro-Asp-NHCH3 and l-N-acetyl-3,4,6-tri-O-acetyl-2-acetamido-2-deoxy-β-D-gluco-pyranosylamine at ambient temperature in acetonitrile. The CD spectrum obtained from the equimolar solution of the above two molecules (the “spectroscopic sum”) was identical with the CD curve obtained from the algebraic summation of the individually recorded CD spectra of the peptide and the carbohydrate moiety (“mathematical sum”).The global picture of the CD spectral analyses of the eight parent peptides with the eight N-glycopeptides revealed that in trifluoroethanol and acetonitrile, the side-chain modification of the Asn models (natural N-glycopeptide analogues) by N-glycosylation has a significant effect on the conformation of the carrier peptide, resulting in a decrease in the original type I β-turn content. Simultaneously, the type II β-turn conformational percentage increased to ≈ 20%. Such a conformational ratio change seems to be larger than the expected errors arising from the CD analyses, and agrees with the results of MD calculations. N-glycosylation of Asn residues causes perturbations, not only through the covalent bond, but also through specific hydrogen bonds between the backbone and side chain atoms. CD spectroscopy, augmented by efficient CD curve deconvolution techniques, has proved to be a useful tool for studying multicomponent conformer mixtures of small linear peptides in solution and changes of conformational equilibria caused by N-glycosylation. © 1993 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360330416
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  • 8
    Electronic Resource
    Electronic Resource
    A search for the ideal type I β-turn (1996)
    New York : Wiley-Blackwell
    Biopolymers 38 (1996), S. 723-732 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In 1968 C. Venkatachalam (Biopolymers, Vol. 6, pp. 1425-1436) predicted the ideal forms of β-turns (type I, type II, etc.) based entirely on theoretical calculations. Subsequently, over a thousand x-ray structures of different globular proteins have been analyzed, with results suggesting that the most important form among the hairpin conformers is the type I β-turn. For the latter type of hairpin conformation, the original computations had predicted φi+1 = -60°, ψi+1 = -30°, φi+2 = -90°, and ψi+2 = 0° as backbone torsion angle values, and these have been used from that time as reference values for the identification of the type I β-turn. However, it has never been clarified whether these “ideal” backbone torsion angle values exist in real structures, or whether these torsion angles are only “theoretical values.” Using the most recent release of the Protein Data Bank (1994), a survey has been made to assign amino acid pairs that approach the ideal form of the type I β-turn. The analysis resulted in four sequences where the deviation from ideal values for any main-chain torsion angles was less than 2°. In order to determine whether such a backbone fold is possible only in proteins owing to fortuitous cooperation of different folding effects, or whether it occurs even in short peptides, various attempts have been made to design the optimal amino acid sequence. Such a peptide model compound adopting precisely the predicted torsion angle values [φi+1 = -60°, ψi+1 = -30°, φi+2 = -90°, and ψi+2 = 0°] could provide valuable information. The solid state conformation of cyclo[(δ) Ava-Gly-Pro-Thr (O1Bu)-Gly] reported herein, incorporating the -Pro-Thr- subunit, yields values suggesting that the “ideal” type I β-turn is even possible for a peptide where there are no major environmental effects present. © 1996 John Wiley & Sons, Inc.
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  • 9
    Electronic Resource
    Electronic Resource
    CD and Fourier transform ir spectroscopic studies of peptides. II. Detection of β-turns in linear peptides (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 177-185 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Comparative CD and Fourier transform ir (FTIR) spectroscopic data on N-Boc protected linear peptides with or without the (Pro-Gly) β-turn motif (e.g., Boc-Tyr-Pro-Gly-Phe-Leu-OH and Boc-Tyr-Gly-Pro-Phe-Leu-OH) are reported herein. The CD spectra, reflecting both backbone and aromatic contributions, were not found to be characteristic of the presence of β-turns. In the amide I region of the FTIR spectra, analyzed by self-deconvolution and curve-fitting methods, the β-turn band shewed up between 1639 and 1633 cm-1 in trifluoroethanol (TFE) but only for models containing the (Pro-Gly) core. This band war-also present in the spectra in chloroform but absent in dimethylsulfoxide. These findings, in agreement with recent ir data on cyclic models and 310-helical polypeptides and protein in D2O [see S. J. Prestrelski, D. M. Byler, and M. P. Thompson (1991), International Journal of Peptide and Protein Research, Vol. 37, pp. 508-512; H. H. Mantsch, A. Perczel. M. Hollósi, and G. D. Fasman (1992), FASEB Journal, Vol. 6, p. A341; H. H. Mantsch. A. Perczel, M. Hollósi, and G. Fasman (1992), Biopolymers. Vol. 33, pp. 201-207; S. M. Miick, G. V. Martinez, W. R. Fiori, A. P. Tedd, and G. L. Millhauser (1992). Nature, Vol. 359, pp. 653-655], suggest that the amide I band, with a major contribution from the acceptor C = O of the 1 ← 4 intramolecular H bond of β-turns, appears near or below 1640 cm-1, rather than above 1660 cm-1. In TFE, bands between 1670 and 1660 cm-1 are mainly due to “free” carbonyls, that is, C = O's of amides that are solvated but not involved in the characteristic H bonds of periodic secondary structures or β-turns. © 1994 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360340204
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  • 10
    Electronic Resource
    Electronic Resource
    A SIMS and AES examination of a Cu/Co/Si alloyPaper presented at Surface Analysis 79, Karlovy Vary, Czechoslovakia, 12-15 June 1979. (1979)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 1 (1979), S. 139-143 
    Details
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The present paper deals with SIMS and AES examination of the layer structure developing during the annealing of a Cu/Co/Si alloy. It was discovered from the spectra and Auger images that there is a significant local increase of the concentration of the alloying materials. A surface layer develops during heat treatment of the alloy sample. We prove the presence of CoSi clusters and the joint enrichment of Si and Co.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/sia.740010502
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