Chemistry of Synthetic Bilayer Membranes

The preparation of bilayer membranes from synthetic dialkyl amphiphiles is described. According to the electron microscopic observation, the bilayer structure similar to that of biomembranes is formed spontaneously when dialkyldimethyl-ammonium bromides with C₁₀-C₂₀ alkyl groups are dispersed in water by sonication. The line broadening in the NMR spectrum strongly suggests that these synthetic bilayers constitute liquid crystalline or solid phases. The hydrophilic head group may be sulfonium and modified ammonium moieties. The bilayer assembly is also formed from dialkyl amphiphiles with anionic head groups: (phosphate, sulfonate, and carboxylate), from nonionic dialkyl amphiphiles (oligomeric ethylene oxide) moiety) and from zwitterionic dialkyl amphiphiles. These bilayers incorporate equimolar cholesterol fairly readily. The redistribution of catalyst (a cholesterol derivative) and substrate (p-nitrophenyl palmitate) molecules is very slow when they are tightly bound to the aggregate. The intravesicle reaction is much faster than the intervesicle counterpart in the case of the di-dodecyldimethylammonium bromide vesicle.