Optical rotatory behavior of polypeptide solutions in the liquid crystal and pretransitional regions

Abstract

The optical rotatory behavior of solutions of the synthetic polypeptides poly‐γ‐benzyl‐l‐glutamate (PBLG) and poly‐γ‐benzyl‐d‐glutamate (PBDG) was studied in various solvents as a function of wavelength, concentration of polymer and temperature. The specific rotation in the liquid crystal was found to be inversely proportional to the pitch of the cholesteric structure and therefore does not follow the deVries equation previously thought to describe the optical rotatory dispersion of these liquid crystals. Solutions of PBLG and PBDG were also examined in the pretransitional region at concentrations just below the critical point for the formation of cholesteric spherulites. An enhancement of the optical rotatory power was observed which is attributable to short range chiral ordering of the long axes of the macromolecules. The sense of the emergent chiral ordering is strongly solvent dependent but the effects may be separated into three solvent classifications. Residual form optical activity was also found in the pretransition region of racemic mixtures of PBLG and PBDG in each solvent class.