Side-chain dynamics in poly(alpha-glutamate) and poly(gamma-glutamate) aqueous solutions: a high-frequency dielectric investigation

The side-chain dynamics in two polypeptides, poly(cl-glutamate) and poly(ga mma-glutamate), in aqueous solutions were investigated by means of dielectr ic spectroscopic measurements carried out in the frequency range from 1 MHz to 1.8 GHz. The influence of the conformational transitions induced by pH was studied and the behaviour of the dielectric parameters of the observed dielectric dispersion (the dielectric increments and the relaxation times) as a function of the degree of ionization is discussed. These results sugge st that the motion of the side-chain groups in both polymers is largely ind ependent of the chain conformation, i.e., of the fraction of the helical co ntent in the polymer chain. The findings indicate that the cooperative coup ling mechanism between several repeat units in the coiled part of the chain , recently reported for similar polymers to take into account the observed dielectric relaxation, is invalid.