The optical rotation and molecular configuration of synthetic polypeptides in dilute solution

Abstract

The optical rotations of a number of synthetic polypeptides have been measured in a variety of solvents. For each polypeptide species, a number of copolymers of different D:L compositions have been examined. Several distinct types of behaviour have been found, which may readily be interpreted in terms of the relative stability of left-handed helices, right-handed helices, and random coils. In solvents that are not too polar (even for quite considerable departures from the enantiomorph) predominantly L polymers exist entirely as right-handed helices. The rotation of a right-handed helical form of several meso polypeptides has been deduced; this rotation varies somewhat from polymer to polymer but is not markedly dependent on the solvent. It appears that the solvated D and I residues on a meso helical polypeptide largely cancel out each other’s contributions to the rotation. The dispersion of the right-handed helical form of poly-DL-leucine has been derived.