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Secondary structure of peptides. 18. 15 N‐nmr and 13 C‐nmr CP/MAS investigation of the primary and secondary structure of (Ala/Val) copolypeptides
Author(s) -
Kricheldorf Hans R.,
Müller Detlef,
Hull William E.
Publication year - 1985
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360241108
Subject(s) - chemistry , protein secondary structure , monomer , nmr spectra database , crystallography , trifluoroacetic acid , benzylamine , carbon 13 nmr , nuclear magnetic resonance spectroscopy , proton nmr , two dimensional nuclear magnetic resonance spectroscopy , stereochemistry , spectral line , organic chemistry , polymer , biochemistry , physics , astronomy
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 1 H‐nmr spectroscopic end‐group analyses and viscosity measurements. The sequences were characterized by 15 N‐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 13 C‐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 13 C‐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.