Synthetic bilayer membranes prepared from dialkyl amphiphiles with nonionic and zwitterionic head groups

Dialkyl amphiphiles with nonionic and zwitterionic head groups were prepared. The nonionic group is the polyoxyethylene chain and the zwitterionic group is composed of the combinations of ammonium sulfonate, ammonium phosphate, and ammonium amidate. These dialkyl amphiphiles, when dissolved in water, produced very large aggregates as determined by small-angle light scattering: 1-50 million daltons. The critical micelle concentration was 10^-5- 10^-6 M. The aggregate morphology was examined by electron microscopy. In the case of the nonionic amphiphile, the chain lengths of both the polyoxyethylene and dialkyl groups were shown to affect the morphology. When the alkyl chain length was C₁₂, C₁₄, C₁₆, and C₁₈ (but not C₈), the bilayer formation was observed, and vesicles, lamellae, and disks were found depending on the amphiphile structure. The zwitterionic amphiphiles similarly produced vesicles and lamellae. Most of these aggregates showed the phase transition phenomenon (solid-liquid crystal). The transition temperature rose with increasing alkyl chain lengths in general agreement with that of lecithin.