Solution behavior of homopolymers and random copolymers of l‐methionine and s‐ethyl‐l‐cysteine

Abstract

AbstractSynthesis and conformational studies of polypeptide homopolymers and random copolymers of L‐methionine and S‐ethyl‐L‐cysteine are reported. Syntheses were carried out by sodium methoxide initiation of the N‐carboxyanhydrides of the α‐amino‐acids dissolved in nitrobenzene. The polymers were studied in solution by classical techniques: optical rotatory dispersion, viscometry, light scattering, and spectrophotometry. The effect of the solvent composition on the helix‐random coil transition for poly (L‐methionine) indicates that this polypeptide is still about 60% helical in pure dichloroacetic acid (DCA). Similar behavior of random copolymers containing 60% or more of L‐methionine is observed. The infrared spectra indicate the “β‐structure” of poly (S‐ethyl‐L‐cysteine) and random copolymers rich in S‐ethyl‐L‐cysteine. The influence of solvent composition on the conformational behavior of these polymers is slight. Weight‐average molecular weight and radius of gyration have been determined in pure DCA. In the case of poly (L‐methionine) the experimental observations agree with the interrupted‐helix model.