QUATERNARY AMMONIUM DERIVATIVES OF CHOLESTEROL - POLYMERIZATION AND VESICLE FORMATION

The ability of nine amphiphilic quaternary ammonium derivatives of cholesterol to form small unilamellar vesicles in water has been investigated using the entrapment of [C-14]sucrose coupled with gel filtration. In all cases vesicles were detected and the proportion of [C-14]sucrose entrapped suggested that these were indeed of the small unilamellar type. In the case of one amphiphile with a pyridinium ion head-group, studies over a period of four weeks showed the vesicles to be very stable, although there was some evidence for fusion and growth of the lamellar structures. Five of the amphiphiles also contained a polymerizable methacrylate group. Photoinitiation of polymerization of these in aqueous dispersions using 2,2-dimethoxy-2-phenylacetophenone as the initiator yielded only oligomeric products with DP(n) approximately 5-13. In contrast polymerization in isotropic benzene solutions using thermal fragmentation of azobisisobutyronitrile yielded polymers with DP(n) up to approximately 180. In aqueous solution the 'rigid' bilayer structures may impose some additional steric restriction to polymer growth, a restriction that is absent in benzene solutions.