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Nuclear magnetic resonance investigation of the helix to random coil transformation in poly‐α‐amino acids. I. Poly‐ L ‐alanine
Author(s) -
Ferretti James A.,
Paolillo Livio
Publication year - 1969
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.1969.360070203
Subject(s) - trifluoroacetic acid , chemistry , random coil , helix (gastropod) , alanine , peptide , solvent , chloroform , amino acid , nuclear magnetic resonance spectroscopy , crystallography , nuclear magnetic resonance , stereochemistry , circular dichroism , organic chemistry , ecology , biochemistry , physics , snail , biology
High‐resolution nuclear magnetic resonance spectra at 100 MHz and 220 MHz have been obtained on two samples of poly‐ L ‐alanine of differing molecular weights (2500 and 42 500) in the chloroform–trifluoroacetic acid system under various conditions of solvent composition, temperature, and polypeptide concentration. Separate helix and random coil peaks are observed for the α‐CH and peptide NH backbone proton resonances, thereby permitting the determination of helix content. This observation of separate peaks demonstrates that the lifetimes of the helix and random coil portions of poly‐ L ‐alanine have lower limits of about 10 −1 sec. It is suggested that solvent–peptide versus peptide–peptide hydrogen bond competition, coupled with a destabilizing effect of the trifluoroacetic acid on the helix, is responsible for the helix–random coil transformation.