Electric and hydrodynamic properties of polypeptides in solution. 3. Aggregation of poly(L-glutamic acid) in aqueous methanol solvents studied by electric birefringence.

Abstract

AbstractThe rise and decay of electric birefringence for poly(L‐glutamic acid) (PLGA) in aqueous solvents containing 20 and 10 vol % methanol have been found to be unusual. The decay curves have been analyzed on the assumption that there exist two kinds of particles, namely, one (component I) with a shorter relaxation time exhibiting positive birefringence and the other (component II) with a longer relaxation time exhibiting negative birefringence at low fields. From the field strength dependence of the steadystate birefringence the permanent dipole moment, the anisotropy of electric polarizability, and the saturation value of birefringence have been determined for each component. Furthermore, from the relaxation time the length of component I and the diameter of component II have been computed on the models of cylindrical rod and oblate ellipsoid, respectively. The dipole moment, the anisotropy of electric polarizability, and the relaxation time of component II are much larger than those of component I. Both the anisotropy of electric polarizability and the optical anisotropy factor are positive in sign for component I and negative for component II. It is concluded that component I is the helical PLGA molecule itself and component II is the side‐by‐side (antiparallel) aggregate composed of many helical PLGA molecules. The optical anisotropy factor of each component has been discussed on the basis of Peterlin‐Stuart theory.