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Kinetics for the transition between cis ‐ and trans ‐helices in poly‐ L ‐proline
Author(s) -
Rifkind Joseph M.
Publication year - 1970
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.1970.360090904
Subject(s) - chemistry , nucleation , kinetics , isomerization , solvent , crystallography , helix (gastropod) , reaction rate constant , stereochemistry , thermodynamics , organic chemistry , catalysis , ecology , physics , quantum mechanics , snail , biology
The kinetics for the cis ‐ trans isomerization of long‐chain poly‐ L ‐proline has been studied as a function of pressure, temperature, and solvent composition in the acetic acid + n ‐propanol solvent system. Our complete kinetic curves were fitted by Monte Carlo techniques, and rate constants for nucleation, growth, and termination were estimated. It was found that for the formation of a cis ‐helix, high pressure, low temperature, and increased acetic acid content of the solvent, lowered the rate of nucleation relative to growth. The inverse seems to be t rue for the formation of a trans ‐helix. Molecular models suggest that this behavior of the kinetic constants can be due to the exposure of peptide units to solvent in the transition state for trans nucleation, and the burying of peptide units in the transition state for cis nucleation. It is further suggested from our analysis of complete kinetic curves that at least one of the assumptions usually made in the analysis of relaxation kinetics is invalid for poly‐ L ‐proline.