Deuteration and solvent composition effects in the helix–coil transition of poly‐γ‐beiizyl‐L‐glutamate

The effects of deuteration and of changes in solvent composition on the thermo dynamics of the helix–coil transition have been studied by calorimetric and optical measurements in the poly‐γ‐benzyl‐ L ‐glutamate–dichloroacetic acid–1,2‐dichloro‐ethanc system. For a given solvent composition, deuteration of the polypeptide and of the acid lowers the transition temperature T c , while an increase in the volume fraction of acid in the solvent raises T c . A rise in T c is accompanied by a decrease in both the van't Hoff and the calorimetric heats of transition, but at different rates. The result is a temperature dependency in the Zimm‐Bragg cooperation parameter σ. Possible causes of this result and its implications are discussed.