DSC Study of the Conformational Transition of Poly-γ-Benzyl-L-Glutamate in the System: 1,3-Dichlorotetrafluoroacetone-Water

Abstract

The helix-coil transition in homopolypeptides is of interest not only because of its obvious relevance to in vivo processes in biological systems but also because it serves as a useful model for co-operative transitions in general, with the attractive simplification of a quasi-one dimensionality, and because of the opportunities it affords for the study of hydrogen bonding and other non-covalent interactions in polymers under reasonably well-defined conditions. For these, and other reasons, a substantial body of experimental and theoretical observations in this area has been accumulated in the past decade and a half, (1,2): A large fraction of the experimental research in model homopoly-α-amino acids has concentrated on non-ionizable polymers soluble in organic solvent systems. These offer a simplicity in the presumed molecular mechanism of transition, which may be conceived simply in terms of competitive intra-molecular (peptide-peptide) and inter-molecular (peptide-solvent) interactions. In the absence of the latter, the order-disorder transition would still occur because of the gain in entropy afforded by conversion to the latter phase, but for most known polypeptides the transition would take place at an inconveniently high temperature.