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  • Polymer and Materials Science  (5)
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  • 1
    Electronic Resource
    Electronic Resource
    Secondary structure of peptides. 18. 15N-nmr and 13C-nmr CP/MAS investigation of the primary and secondary structure of (Ala/Val) copolypeptides (1985)
    New York : Wiley-Blackwell
    Biopolymers 24 (1985), S. 2113-2129 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Various copolypeptides were prepared by benzylamine or tertiary amine-initiated copolymerizations of alanine-N-carboxyanhydride (Ala-NCA) and valine-N-carboxyanhydride (Val-NCA). The number-average molecular weights of these copolypeptides were detemined by 1H-nmr spectroscopic end-group analyses and viscosity measurements. The sequences were characterized by 15N-nmr spectra in solution, and the average lengths of the homogeneous blocks were determined from the signal intensities. The 50.3-and 75.4-MHz 13C-nmr CP/MAS spectra of the solid copolypeptides are not sensitive to sequence effects, but allow qualitative and quantitative analyses of the secondary structures. In contrast to other methods, the 13C-nmr spectra allow determination of the extent to which individual amino acids are incorporated into β-sheet or α-helix phases. Depending on primary structure and molecular weight, the secondary structure of (Ala/Val) copolypeptides may vary significantly. Both monomer units may be predominantly helical or predominantly β-sheet structure, or the Val units may prefer the β-sheet structure with most Ala-units forming β-helices. However, these secondary structures are more or less thermodynamically unstable and revert to the stable conformations on reprecipitation from trifluoroacetic acid/water.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360241108
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  • 2
    Electronic Resource
    Electronic Resource
    Secondary structure of peptides. 4: 13C-Nmr CP/MAS investigation of solid oligo- and poly(L-alanines) (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 1357-1372 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Primary and tertiary amine-initiated polymerizations of L-alanine-N-carboxyanhydride (L-Ala-NCA) were conducted at 20 or 100°C in a variety of solvents. The 75.5-MHz 13C-nmr CP/MAS spectra of the resulting poly(L-alanines) revealed that all samples contain both α-helix and pleated-sheet structures. Depending on the reaction conditions the α-helix content varied between ca. 1 and 99%. Reprecipitation from aprotic nonsolvents does not change the α-helix/β-sheet ratio, indicating that this ratio is thermodynamically controlled. Since relatively large amounts of oligopeptides of degree of polymerization (DP) 4-6 can be extracted by means of acetic acid, it is concluded that (a) most poly(L-alanines) possess a bimodal molecular weight distribution, (b) the oligopeptide fraction with DP ≤ 11 is responsible for the β-sheet fraction of all samples, and (c) the two-stage crystal growth proposed by Komoto and Kawai is not correct. Solubilizing initiators such as poly(ethylene oxide) NH2 prevent the precipitation of oligoalanine and, thus, the formation of a β-sheet structure. 13C-nmr CP/MAS measurements also show that tri- and tetra-L-alanines form insoluble β-sheet structures.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360220508
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  • 3
    Electronic Resource
    Electronic Resource
    Secondary structure of peptides, 11Part 10.: J. Stulz, D. Müller, H. R. Kricheldorf; Makromol. Chem. 184, 1311 (1983).. How to synthesize helical poly(L-phenylalanine)? (1983)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 184 (1983), S. 1407-1421 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Polymerizations of L-phenylalanine-N-carobxyanhydride(L-Phe-NCA) were conducted under various reaction conditions and the secondary structure of the resulting solid poly(L-phenylalanine)s was examined by means of 50,3 or 75,4 MHz 13C NMR CP/MAS spectra. When primary alkylamines were used as initiators only α-helix contents ≤ 60% were obtained regardless of solvent and temperature. However, a part of the β-sheet structures was thermodynamically unstable and could be converted into α-helices by reprecipitation. An α-helix content 〉 90% was achieved only when weakly nucleophilic reagents, such as aromatic amines or water, were used as initiators in methylene chloride. A kinetic explanation of these results is discussed. Aprotic bases gave low yields of poly(L-phenylalanine) and substantial amounts of low molecular weight side products. An α-helix content ≥ 95%, was achieved when L-Phe-NCA was polymerized in pyridine at 100°C. The usefulness of IR spectra for the characterization of the secondary structure of poly(L-phenylalanine) is discussed.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1983.021840709
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  • 4
    Electronic Resource
    Electronic Resource
    Secondary structure of peptides, 14Part 13: H. R. Kricheldorf and W. E. Hull, Int. J. Biol. Macromol. 6, 81 (1984).. FT-IR and 13C NMR CP/MAS investigation of the helix stability of solid poly(L-proline)s (1984)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 185 (1984), S. 1739-1749 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Primary amine and pyridine-initiated polymerizations of L-proline-N-carboxyanhydride (Pro-NCA) at 20 or 100°C yield exclusively or predominantly 103-helices. Only primary amine-initiated polymerizations in 1,4-dioxane at 100°C result in partial formation of 31-helices. The stability of both 103- and 31-helices against conformational transitions was investigated in various organic non solvents or salt solutions at 100 or 150°C. A 103 → 31 transition was only observed in protic non solvents such as formamide, water, or propionic acid, but not in alcohols. A 31 → 101 helix transition was observed in alcohols and most aprotic solvents but not in formamide, water, or propionic acid. Hence, it is concluded that the formation of 31 helices by primary amine-initiated polymerizations in 1,4-dioxane at 100°C is a kinetically controlled consequence of the reaction mechanism. The usefullness of 13C NMR CP/MAS spectra and Fourier-Transform IR spectra for the quantitative analysis of composed secondary structures is compared and discussed.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1984.021850820
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  • 5
    Electronic Resource
    Electronic Resource
    Secondary structure of peptides, 10Part 9: H. R. Kricheldorf, D. Müller, K. Ziegler, Polym. Bull. 9, 284 (1983).. FT-IR and 13C NMR CP/MAS study on tacticity and secondary structure of poly(D,L-leucine)s (1983)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 184 (1983), S. 1311-1322 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A series of poly (L-leucine)s with average degrees of polymerization in the range between 10 and 100 and various poly (D,L-leucine)s were prepared by polymerization of L-leucine-N-carb-oxyanhydride (NCA) or D,L-Leu-NCA. The FT-IR spectra measured in KBr show that the amide I and II bands are exclusively sensitive to the secondary structure of the poly (leucine)s and not to their tacticity. The tacticities of the poly(D,L-leucines) were determined in solution of trifluoroacetic acid by means of 13C NMR spectra, while 13C NMR CP/MAS spectra of the solid polymers revealed that the poly(D,L-leucine)s contain 40 - 60 wt.- % α-helix structure. For this reason the broad amide I and II bands do not enable one to distinguish isotactic and more or less atactic poly(leucine)s. However, the IR-bands between 500 and 900 cm-1 allow a differentiation between poly(L-leucine) and poly(D,L-leucine)s and also between poly(D,L-leucine)s of different tacticity. The IR-spectra confirm that primary amine-initiated polymerizations of D,L-Leu-NCA do not lead to long stereo blocks.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1983.021840622
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