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Structure of aggregates and helix–coil transition of polypeptides by dielectric measurements. II. Poly‐ D , L ‐phenylalanine and poly‐β‐benzyl‐ L ‐aspartate in chloroform–dichloroacetic acid mixtures
Author(s) -
Marchal E.
Publication year - 1974
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.1974.360130703
Subject(s) - dichloroacetic acid , chemistry , chloroform , helix (gastropod) , solvent , polymer , circular dichroism , dissociation (chemistry) , dipole , dielectric , polymer chemistry , crystallography , organic chemistry , ecology , snail , biology , physics , optoelectronics
The dielectric absorption of poly‐ DL ‐phenylalanine and poly‐γ‐benzyl‐ L ‐aspartate (PLAB) was measured in very dilute solutions to determine the type of molecular association and to locate the helix–coil transition. Both polypeptides were present as associated helices in chloroform. The mode of aggregation, which was determined by measuring the dipole moment and the critical frequency, did not depend on the polarity of the side chain but rather on that of the solvent. In both polymers, the dissociation of the aggregates in chloroform was observed on addition of small amounts of dichloroacetic acid; further addition of the acid lead to the helix–coil transition. No second region of dielectric absorption that might be related to the kinetics of the transition was found during the helix–coil transition of PBLA.