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Local conformations of ends of α‐helical poly[Glu(OBzl)] studied by circular dichroism of terminal chromophores
Author(s) -
Shimizu Toshimi,
Sisido Masahiko,
Imanishi Yukio,
Higashimura Toshinobu
Publication year - 1980
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.1980.360190703
Subject(s) - chemistry , circular dichroism , chromophore , dimer , dichloroacetic acid , helix (gastropod) , stereochemistry , crystallography , photochemistry , organic chemistry , ecology , snail , biology
Conformations of terminal peptide units of α‐helical poly(γ‐benzyl‐ L ‐glutamate), poly‐[Glu(OBzl)], were examined by an induced circular dichroism (CD) of chromophores which were covalently attached to both ends of the chain. In chloroform, where the helical poly‐[Glu(OBzl)] exists as a head‐to‐tail‐type dimeric associate, the chromophores showed a strong CD induced by an asymmetric perturbation from the helical structure. The induced CD almost disappeared by an addition of a few percent of dichloroacetic acid, which has been reported as a powerful breaker of the associate. These results are explained by an incorporation of terminal peptide units into a helical conformation in the head‐to‐tail associate and a local unfolding of the terminal portions by the addition of acid. An induced CD of a charge‐transfer complex between the two terminal chromophores was also observed and the structure of the helix–helix junction of the head‐to‐tail dimer is discussed.