Conformation and molecular motion of poly(l-glutamate) with long n-alkyl side chains in the solid state and the liquid crystalline state as studied by high-resolution 13C NMR spectroscopy

Abstract

Abstract 13 C CP/MAS and PST/MAS NMR experiments are carried out on poly(γ- n -octadecyl l -glutamate) (POLG) over a wide range of temperatures from −40 to 230°C to elucidate dynamical and conformational features in the solid state and the liquid-crystalline state, in addition to the experimental findings reported previously. From these experimental results it was found that as the temperature is increased and the methylene carbons of the n -alkyl side-chains are away from the main-chain, the gauche fraction is increased but the magnitude of its temperature change is decreased. Furthermore, from the experimental results on the temperature dependence of the 13 C chemical shift of the main-chain carbonyl carbon, it was found that the main-chain takes the right-handed α-helix form in the temperature range from −40 to 230°C, and that as the temperature is increased, the amide hydrogen-bond length in the main-chain is increased slightly.