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  • 1
    Digitale Medien
    Digitale Medien
    Comment on the Berkeley kinetic network model (1985)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 25 (1985), S. 782-787 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: A kinetic model for the rheological behavior of polymeric systems, i.e. the Berkeley kinetic network model, is compared with a generalized transient-network model. It turns out that the Berkeley kinetic network model fits quite well in the framework of the transient-network model. From the point of view of the latter model, however, a number of parameters introduced in the kinetic-network model are not independent constants as was supposed. Since the generalized transientnetwork model is totally based on microscopic assumptions, the parameters in this theory reveal information about the structure, whereas the physical interpretation of the parameters in the kinetic model is vague. Stress predictions of the generalized transient-network model agree with experimental data from a 4 percent solution of polystyrene in arochlor, obtained from literature.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760251210
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  • 2
    Digitale Medien
    Digitale Medien
    Conformational Characterization of the 1-Aminocyclobutane-1-carboxylic Acid Residue in Model Peptides (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 3 (1997), S. 110-122 
    Details
    ISSN: 1075-2617
    Schlagwort(e): β-bend ; cyclic amino acid ; 310-helix ; peptide conformation ; X-ray diffraction ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A series of N- and C-protected, monodispersed homo-oligopeptides (to the dodecamer level) from the small-ring alicyclic Cα,α-dialkylated glycine 1-aminocyclobutane-1-carboxylic acid (Ac4c) and two Ala/Ac4c tripeptides were synthesized by solution methods and fully characterized. The conformational preferences of all the model peptides were determined in deuterochloroform solution by FT-IR absorption and 1H-NMR. The molecular structures of the amino acid derivatives Z-Ac4c-OH and Z2-Ac4c-OH, the tripeptides Z-(Ac4c)3-OtBu, Z-Ac4c-(L-Ala)2-OMe and Z-L-Ala-Ac4c-L-Ala-OMe, and the tetrapeptide Z-(Ac4c)4-OtBu were determined in the crystal state by X-ray diffraction. The average geometry of the cyclobutyl moiety of the Ac4c residue was assessed and the τ(N-Cα-C′) bond angle was found to be significantly expanded from the regular tetrahedral value. The conformational data are strongly in favour of the conclusion that the Ac4c residue is an effective β-turn and helix former. A comparison with the structural propensities of α-aminoisobutyric acid, the prototype of Cα,α-dialkylated glycines, and the other extensively investigated members of the family of 1-aminocycloalkane-1-carboxylic acids (Acnc, with n=3, 5-8) is made and the implications for the use of the Ac4c residue in conformationally constrained peptide analogues are briefly examined. © 1997 European Peptide Society and John Wiley & Sons, Ltd
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Inversion of 310-helix screw sense in a (D-αMe)Leu homotetrapeptide induced by a guest D-(αMe)val residue (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 1 (1995), S. 396-402 
    Details
    ISSN: 1075-2617
    Schlagwort(e): (αMe) amino acids ; CD spectroscopy ; 310-helix ; peptide 3D-structure ; X-ray structure ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The terminally blocked tetrapeptide pBrBz-[D-(αMe)Leu]2-D-(αMe)Val-D-(αMe)Leu-OtBu is folded in the crystal state in a left-handed 310-helical structure stabilized by two consecutive 1 ← 4 C=O⃛H—N intramolecular H-bonds, as determined by X-ray diffraction analysis. A CD study strongly supports the view that this conformation is also that largely prevailing in MeOH solution. A comparison with the published conformation of pBrBz-[D-(αMe)Leu]4-OtBu indicates that incorporation of a single internal β-branched (αMe)Val guest residue into the host homo-tetrapeptide from the γ-branched (αMe)Leu residue is responsible for a dramatic structural perturbation, i.e. an inversion of the 310 screw sense from right to left-handed.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/psc.310010607
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  • 4
    Digitale Medien
    Digitale Medien
    Conformation and membrane activity of an analogue of the peptaibol antibiotic trichogin GA IV with a lipophilic amino acid at the N-terminus (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 4 (1998), S. 389-399 
    Details
    ISSN: 1075-2617
    Schlagwort(e): conformational analysis ; lipo-amino acid ; membrane activity ; NMR ; peptide antibiotic ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: We have synthesized by solution-phase methods two analogues of the 11-residue lipopeptaibol antibiotic trichogin GA IV in which the N-terminal n-octanoyl group is replaced either by an N-acetylated 2-amino-2-methyl-l-undecanoic acid or by an N-acetylated α-aminoisobutyric acid. CD, FTIR absorption, and NMR analyses unequivocally show that the main structural features of trichogin GA IV are preserved in these analogues. Since only the peptide containing the lipophilic chain exhibits membrane-modifying properties, these results strongly support the view that moving the long acyl moiety from the Nα-blocking group to the side chain of the N-terminal extra-residue does not affect the conformational properties or the membrane activity of trichogin GA IV. © 1998 European Peptide Society and John Wiley & Sons, Ltd.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Peptide helices as rigid molecular rulers: A conformational study of isotactic homopeptides from α-methyl-α-isopropylglycine, [L-(αMe)Val]nLinear Oligopeptides, Part 360. Part 359: A. Bianco, M. Maggini, G. Scorrano, C. Toniolo, G. Marconi, C. Villani, M. Prato, J. Am. Chem. Soc. 1996, 118, 4072-4080. (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1104-1111 
    Details
    ISSN: 0947-6539
    Schlagwort(e): amino acids ; conformation ; helices ; molecular rulers ; oligopeptides ; structure elucidation ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Terminally blocked, isotactic homopeptides from the sterically demanding α-methylvaline of general formula Y-[L-(αMe)Val]n-OtBu (Y = Z, pBrBz, Ac; n = 2-8) have been prepared step-by-step in solution and fully characterized. The conformations preferred in solution (β-turn and right-handed 310-helix) have been assessed by FT-IR, 1H NMR and CD spectroscopy. The molecular and crystal structures of the Z-protected trimer, hexamer, heptamer and octamer have been determined by X-ray diffraction. In the crystal state, while the trimer is folded in a type III β-turn conformation, the longest homopeptides form well-developed, regular, right-handed 310-helices. The screw sense in the helix of the pBrBz-blocked octamer has been confirmed to be right-handed by solid-state and solution CD spectroscopy. The possible exploitation of these peptide helices as rigid and precise molecular rulers is discussed.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.1460020909
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  • 6
    Digitale Medien
    Digitale Medien
    Effect of phenyl ring position in the Cα-methylated α-amino acid side chain on peptide preferred conformation (1996)
    New York : Wiley-Blackwell
    Biopolymers 40 (1996), S. 523-527 
    Details
    ISSN: 0006-3525
    Schlagwort(e): 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
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 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
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Solid-state CD and peptide helical screw sense (1996)
    New York : Wiley-Blackwell
    Biopolymers 38 (1996), S. 301-304 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: No abstract.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Helical screw sense of peptide molecules: The pentapeptide system (Aib)4/L-Val[L-(αMe)Val] in the crystal state (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 433-443 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Aib peptides ; crystal state structure ; helical peptides ; peptide helices ; x-ray crystallography ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The crystal-state preferred conformations of six Nα-blocked pentapeptide esters, each containing four helicogenic, achiral α-aminoisobutyric acid (Aib) residues followed by one chiral L-valine (L-Val) or Cα-methyl-L-valine [(αMe)Val] residue at the C-terminus, have been assessed by x-ray diffraction analysis. In all of the compounds the —(Aib)4— sequence is folded in a regular 310-helical conformation. In the four pentapeptides characterized by the L-(αMe)Val residue two conformationally distinct molecules occur in the asymmetric unit. Conversely, only one molecule is observed in the asymmetric unit of two pentapeptides with the C-terminal L-Val residue. In the L-Val based peptides the helical screw sense of the —(Aib)4— sequence is right-handed, whereas in the L—(αMe)Val— analogues both right- and left-handed helical screw senses concomitantly occur in the two crystallographically independent molecules. © 1998 John Wiley & Sons, Inc. Biopoly 46: 433-443, 1998
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Preferred conformation of peptides rich in alicyclic Cα,α-disubstituted glycines (1996)
    New York : Wiley-Blackwell
    Biopolymers 40 (1996), S. 519-522 
    Details
    ISSN: 0006-3525
    Schlagwort(e): 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
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 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
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Structural versatility of peptides from Cα, α-disubstituted glycines: Crystal-state conformational analysis of homopeptides from Cα-methyl, Cα-benzylglycine [(αMe)Phe]nThis work is part 274 of the Linear Oligopeptides series. For part 273, see Ref. 1. (1993)
    New York : Wiley-Blackwell
    Biopolymers 33 (1993), S. 1617-1625 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The molecular and crystal structures of one derivative and three homopeptides (from the di-to the tetrapeptide level) of the chiral, Cα, α-disubstituted glycine Cα-methyl, Cα-benzylglycine [(αMe)Phe], have been determined by x-ray diffraction. The derivative is mClAc-D-(αMe)Phe-OH, and the peptides are pBrBz-[D-(αMe)Phe]2-NHMe, pBrBz-[D-(αMe)Phe]3-OH hemihydrate, and pBrBz-[D-(αMe)Phe]4-OtBu sesquihydrate. All (αMe)Phe residues prefer φ,ψ torsion angles in the helical region of the conformational map. The dipeptide methylamide and the tripeptide carboxylic acid adopt a β-turn conformation with a 1 ← 4 C=O…H—N intramolecular H bond. The structure of the tripeptide carboxylic acid is further stabilized by a 1 ← 4 C=O…H—O intramolecular H bond, forming an “oxy-analogue” of a β-turn. The tetrapeptide ester is folded in a regular (incipient) 310-helix. In general, the relationship between (αMe)Phe chirality and helix screw sense is opposite to that exhibited by protein amino acids. A comparison is made with the conclusions extracted from published work on homopeptides from other Cα-methylated α-amino acids. © 1993 John Wiley & Sons, Inc.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.360331011
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