Electric and hydrodynamic properties of polypeptides in solution. II. Conformation of poly(L-glutamic acid) in various organic solvents.

Abstract

AbstractThe electric birefringence of poly(L‐glutamic acid) (PLGA) in methanol, dimethyl sulfoxide, dimethylformamide, N‐methylacetamide, trifluoroacetic acid, dioxane–water mixtures (3:1 and 4:1 by volume), and dioxane–formamide mixture (1:1 by volume) has been measured by the use of the rectangular pulse technique at 30 °C. The intrinsic viscosity has also been measured at the same temperature. The magnitude of the specific Kerr constant and the intrinsic viscosity suggests that PLGA is helical and has a large dipole moment in methanol, dimethyl sulfoxide, dimelhylformamide, N‐methylacetamide, and dioxane–water mixtures. In this case we have obtained the length distribution curve and the mean length of PLGA molecules from the decay of the electric birefringence, by applying the method recently developed for helical polypeptides. Furthermore, we have proposed and applied a method of obtaining the mean dipole moment and the optical anisotropy factor from the field strength dependence of the electric birefringence for polydisperse systems on the basis of the knowledge on the length distribution. The results show that PLGA may have a different helical conformation in dimethyl sulfoxide. The specific Kerr constant of PLGA in trifluoroacetic acid is very small, which suggests that PLGA is a random coil in this solvent.