Deuterium N.M.R. studies of polypeptides I. Sidechain orientation in poly(γ-benzyl L-glutamate) and the mechanism of the cholesteric sense inversion

Abstract

The mechanism of thermally- and solvent-induced cholesteric sense inversions in lyotropic polypeptide liquid crystals has been discussed based on deuterium N.M.R. observations for poly(γ-benzyl L-glutamate) with perdeuteriated sidechain benzyl ester groups. Comparison of the deuterium quadrupolar splitting pattern with the macroscopic helical twisting power indicates that the sense inversion does not necessarily require sidechain conformational transitions (or changes in the helix surface chirality). The new data support a less specific mechanism for sense determination in polypeptide liquid crystals: anisotropic intermolecular interactions between helices are influenced by the solvent dielectric medium.