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A nuclear magnetic resonance study of the helix–coil transition of poly( L ‐glutamic acid)
Author(s) -
Lader H. J.,
Komoroski R. A.,
Mandelkern L.
Publication year - 1977
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.1977.360160412
Subject(s) - chemistry , helix (gastropod) , aqueous solution , resonance (particle physics) , proton , proton nmr , spectral line , nmr spectra database , dispersity , asymmetric carbon , crystallography , carbon fibers , nuclear magnetic resonance , stereochemistry , polymer chemistry , organic chemistry , atomic physics , physics , materials science , optically active , quantum mechanics , ecology , astronomy , snail , composite number , composite material , biology
There have been many reports that the nuclear magnetic resonance (nmr) spectra of a large number of polypeptides exhibit peak doubling of the α‐carbon and the α‐carbon proton in the helix–coil transition region. One apparent exception to this generalization has been polypeptides with ionizable side chains, where the helix–coil transition is induced by changes in pH in aqueous solution. Because it is important to establish the proper theoretical reason for the peak doubling and its relation to the rate of conformational change of amino acid residues, we have reexamined the proton and carbon‐13 nmr spectra, at high field, for two polydisperse samples of poly( L ‐glutamic acid). Doubling of the α‐carbon proton resonance as well as those of the α‐ and β‐carbon, and backbone carbonyl are observed for a low‐molecular‐weight sample (DP = 54), while a higher molecular weight sample (DP = 309), exhibits only single resonances. Thus, polydispersity by itself is not sufficient to observe peak doubling; low‐molecular weight is also required.