Conformation of Poly(S-benzyl-l-cysteine) in Solution

Abstract

Conformation of poly(S-benzyl-L-cysteine) was investigated by measurements of optical rotatory dispersion, infrared absorption and viscosity in dichloroacetic acid (DCA)–chloroform mixtures. Transition from random coil to the β-structure was confirmed to occur when DCA content of the solvent was reduced below 40% (v/v). Both dispersion parameters a₀ and b₀ increased as the polymers were transformed into the β-structure. Viscosity of the polymer solution changed only slightly with accompanying the transition. This was interpreted in terms of the formation of intramolecular β-structure. In the region where the β-structure was dominant both optical rotatory parameters and viscosity were independent of solvent composition. Such behavior has been rarely observed in the β-coil transition of other polypeptides. The β-structure of poly(S-benzyl-L-cysteine) was shown to be more stable than that of poly(O-benzyl-L-serine) as referred to respective random coil conformations.