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  • 1
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational analysis of a protected homodipeptide of 1-aminocyclopentanecarboxylic acid (Acc5) has been carried out. 1H-nmr studies establish a β-turn conformation for Boc-Acc5-Acc5-NHMe in chloroform and dimethylsulfoxide solutions involving the methylamide NH in an intramolecular hydrogen bond. Supportive evidence for the formation of an intramolecular hydrogen bond is obtained from ir studies. X-ray diffraction studies reveal a type III β-turn conformation in the solid state stabilized by a 4 → 1 hydrogen bond between the Boc CO and methylamide NH groups. The φ,ψ values for both Acc5 residues are close to those expected for an ideal 310-helical conformation (φ≃ ± 60°, ψ∼ ±30°).
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A newly designed host-guest approach is introduced as a experimental tool to explore the relationship between the sequence of peptides and their secondary structure. From the CD spectra of the host-guest peptides studied, a tentative scale for the α-helix potential in 2,2,2-trifluorethanol of guest amino acids is delineated. The conformational preferences are also examined in β-structure supporting media (solid state, CH2Cl2, CH3OH, H2O) using ir-absorption and CD techniques. Scales for the β-forming tendency of guest amino acid residues in the different media are delineated. It is shown that the preferred conformation of the host-guest peptides is a function of the medium, the chain length, and the protecting groups. Given the fact that conformational effects are important in peptide synthesis, the tentative scales may serve as a guideline to predict secondary structures of side-chain-protected or -deprotected peptides in a given solvent, complementing the well-known empirical conformational prediction parameters.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 182 (1981), S. 941-947 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Monodispersed N-and C-protected linear homo-oligomers of S-methyl-L-cysteine (n = 2 - 7) are studied by measurements of circular dichroism in the vacuum-ultraviolet region. In the solid state higher members of the series take up a β-conformation. The results are compared with earlier circular dichroism and infrared absorption measurements on the same series, and also with the related norvaline and methionine series.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preferred conformation of the Cα,α-diphenylglycine residue was determined in simple derivatives and dipeptides. The dipeptides were synthesized by the 5(4H)-oxazolone (from the N-para-bromobenzoylated amino acid) method. This activated intermediate and a reaction by-product, para-bromobenzoylbenzhydrylamine, were characterized inter alia by x-ray diffraction. Conformational energy calculations on the Cα,α-diphenylglycine mono-peptide, Ac-Døg-NHMe, indicate that this Cα,α-symmetrically disubstituted residue is conformationally restricted and that its minimum energy conformation falls in the fully extended (C5) region. The results of the theoretical analysis are in agreement with the solution and crystal-state structural tendency of mClAc-Døg-OH, Z-Døg-OtBu, pBrBz-Døg-Gly-OMe and its tert-butyl ester analogue, determined by ir absorption, lH-nmr, and x-ray diffraction, and also described in this work. The implications for the use of the Døg residue in designing conformationally constrained analogues of bioactive peptides are briefly discussed.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The molecular and crystal structures of three compounds, representing the repeating units of the β-bend ribbon (an approximate 310-helix, with an intramolecular hydrogen-bonding donor every two residues), have been determined by x-ray diffraction. They are Boc-Aib-Hib-NHBzl, Z-Aib-Hib-NHBzl, and Z-L-Hyp-Aib-NHMe (Aib, α-aminoisobutyric acid; Bzl, benzyl; Boc, t-butyloxycarbonyl; Hyp, hydroxyproline Hib, α-hydroxyisobutyric acid; Z, benzyloxycarbonyl). The two former compounds are folded in a β-bend conformation: type III (III′) for Boc-Aib-Hib-NHBzl, while type II (II′) for the Z analogue. Conversely, the structure of Z-L-Hyp-Aib-NHMe, although not far from a type II β-bend, is partially open.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 32 (1992), S. 453-456 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A survey of literature for the various types of helices experimentally observed in highresolution single crystal x-ray diffraction analyses of peptides has allowed to determine accurate conformational and helical parameters for the various secondary structures such as the α-helix, the 310-helix, the fully extended conformation (25-helix) and the β-bend ribbon spiral. For each of these structures the characteristic φ, ψ conformational parameters, n, the number of residues per turn, h, the height per residues and p, the pitch of the helix are described.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0006-3525
    Keywords: conformational analysis, of peptides ; disubstituted glycines, peptides rich in ; Fourier transform ir absorption, of peptides ; 310-helical conformation, in peptides ; Cα-methylated α-amino acids, peptides rich in ; nmr, of peptides ; peptide conformation ; x-ray diffraction, of peptides ; β-turn conformation, in peptides ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational preferences of the alicyclic Cα,α-disubstituted glycines Acnc (1-amino-1-cycloalkane-carboxylic acid; n = 4, 7, 9, 12) were assessed in selected model compounds, including homopeptides and Ala (or Aib, α-aminoisobutyric acid)/Acnc peptides containing a small total number of residues, by Fourier transform ir absorption, 1H-nmr, and x-ray diffraction analyses. The results obtained indicate that β-turn and 310-helical structures are preferentially adopted by short peptides rich in these cycloaliphatic α-amino acids. © 1997 John Wiley & Sons, Inc. Biopoly 40: 519-522, 1996
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 0006-3525
    Keywords: conformational analysis, of peptides ; disubstituted glycines, peptides rich in ; Fourier transform in absorption, of peptides ; 310-helical conformation, in peptides ; Cα-methylated α-amino acids, peptides rich in ; nmr, of peptides ; peptide conformation ; x-ray diffraction, of peptides ; β-turn conformation, of peptides ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preferred conformations of Cα-methyl phenylglycine, Cα-methyl phenylalanine, and Cα-methyl homophenylalanine residues, as determined in model peptides (including homopeptides) by Fourier transform ir absorption, 1H-nmr, CD, and x-ray diffraction techniques, are compared with the aim of investigating the effect of phenyl ring position in the Cα-methylated amino acid side chain. This study shows that (a) β-turn and 310-helical structures are preferentially adopted by peptides rich in these Cα-methylated, aromatic α-amino acids and (b) turn and helix handedness is critically biased by the position of side-chain branching. © 1997 John Wiley & Sons, Inc. Biopoly 40: 523-527, 1996
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational preferences of the N-trifluoroacetylated homo-peptides of Cα,α-diethylglycine from monomer to pentamer in chloroform solution were determined by using ir absorption and 1H-nmr. Intramolecular hydrogen bonding was found to be the dominant factor for all NH groups. The likely absence of a conformational transition upon increasing main-chain length, and the remarkable stability to dilution, heating, and addition of perturbing agents, are additional relevant findings of this study. These results are in agreement with those of the fully extended, C5-conformation-forming homo-peptides from the higher homolog Cα,α-di-n-propylglycine, but contrast dramatically to those of the homo-peptides from the lower homolog Cα,α-dimethylglycine, which have been shown to adopt the 310-helical structure.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Conformational energy computations on a derivative and a homo-dipeptide of Cα,α-diethylglycine were performed. In both cases the N- and C-terminal groups are blocked as acetamido and methylamido moieties, respectively. It was found that the Cα,α-diethylglycine residues are conformationally restricted and that the minimum energy conformation corresponds to the fully extended C5 structure when the N—Cα—C′ bond angle is smaller than 108° (as experimentally observed). The results of the theoretical analysis are in agreement with the crystal-state structural propensity of the complete series of N-trifluoroacetylated homo-peptides of this Cα,α-dialkylated residue from monomer to pentamer, determined by x-ray diffraction and also described in this work. Interestingly, for the first time, a crystallographically planar peptide backbone was observed (in the protected tripeptide). A comparison with peptides of Cα,α-dimethylglycine, Cα-methyl, Cα-ethylglycine, and Cα,α-di-n-propylglycine indicates that the fully extended conformation becomes more stable than the helical structures when both amino acid side-chain Cβ atoms are substituted.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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