MONOMER TRANSFER AND SOLUBILIZATION OF BILAYER VESICLES FROM DOUBLE-CHAINED AMMONIUM AMPHIPHILES CARRYING AROMATIC UNITS

Double-chained ammonium amphiphiles with terminal (4'-cyanobiphenyl-4- yl)oxy, (4'-cyanoazobenzen-4-yl)oxy, or (4'-nitroazobenzen-4-yl)oxy mo ieties form vesicles upon sonication in water. The UV absorption maxim a of the vesicle dispersions are blue shifted due to formation of H ag gregates of the aromatic units in the bilayer. When these vesicles are mixed with dialkyldimethylammonium bromide vesicles the H aggregates disappear, as can be monitored by UV spectroscopy, By changing the con centration of both vesicle dispersions, it was concluded that the spec tral changes are due to a monomer exchange process instead of a vesicl e fusion process. The same phenomenon was used to monitor the solubili zation of these vesicles by hexadecyltrimethylammonium bromide micelle s, For vesicles from amphiphiles with (cyanobiphenylyl)oxy units at th e termini of both chains, a unidirectional diffusion of monomers to di dodecylclimethylammonium bromide vesicles is found. The reverse proces s is hampered by the rigidity of the bilayer of the former compound du e to stacking of the aromatic units. For vesicles from amphiphiles wit h only one azobenzene unit, the exchange with didodecyldimethylammoniu m bromide vesicles is bidirectional, due to the reduced rigidity of th ese membranes. The monomer exchange with dodecyloctadecyldimethylammon ium bromide and dioctadecyldimethylammonium bromide vesicles is again a unidirectional diffusion of the azobenzene-containing amphiphiles. S olubilization of vesicles from amphiphiles with (cyanobiphenylyl)oxy u nits at the termini of both chains by hexadecyltrimethylammonium bromi de micelles is an unidirectional diffusion process of monomers from th e vesicles to the micelles. Solubilization of vesicles from amphiphile s with only one azobenzene unit is accompanied by penetration of hexad ecyltrimethylammonium bromide monomers into the bilayers.