Electrical Ordering in Polypeptide Solutions

Polypeptides possess large dipole moments when in a helical conformation and can be easily ordered in solution by an electric field. Such ordering results in the material's becoming doubly refractive (the Kerr effect). We have investigated the mode of aggregation of poly-γ-benzyl-L-glutamate dissolved in benzene, dioxane, and ethylene dichloride by measuring the Kerr constant as a function of concentration. From a consideration of this dependence on concentration, the calculated dipole moments of the polymers in these solvents, and the measured intrinsic viscosities, two different modes of aggregation are proposed—a linear association for high dielectric solvents (ethylene dichloride) and a lateral (antiparallel) association for low dielectric solvents (benzene, dioxane).