| Abstract: | 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. |
