Structure of micelles formed by monodisperse hexa-(γ-benzyl-L-glutamate) in solution

The angular dependence of light scattering and the concentration dependence of the relative viscosity have been measured in solutions of o-nitrophenylthio-hexa-(γ-benzyl-L -glutamate) ethylamide in ethylene dichloride. Both the reduced intensity of scattered light and the reduced viscosity of the solution suddenly increase above a certain critical concentration, below which both of them remain low and constant. The Debye plot of light scattering indicates that primary micelles having an aggregation number 48 are formed at the critical micelle concentration and that secondary micelles, each consisting of 294 molecules, then appear in increasing amounts with increasing concentration beyond the critical micelle concentration. The secondary micelle is rodlike and has a length of 1170 Å, if it is rigid. An analysis of the reduced viscosity leads to the intrinsic viscosity for the primary micelle, 0.360 dL g^?1, and to that of the secondary micelle, 1.28 dL g^?1. If the secondary micelle is represented by a prolate ellipsoid, it should have an axial ratio of 47. If the polypeptide chains are extended in the micelle, the observed aggregation number and axial ratio of the secondary micelle can well accommodate the intermolecularly hydrogen-bonded in-register β-structure of anti-parallel chains. In the primary micelle, some folded polypeptide chains are involved, and an intermolecularly hydrogen-bonded out-of-register structure would form a rather open network.