VESICLES AS AN EQUILIBRIUM STRUCTURE OF A SIMPLE SURFACTANT-WATER SYSTEM

Unilamellar vesicles are observed to form spontaneously in dilute wate r solutions of the ganglioside GM3, which is a double-tailed biologica l amphiphile with a saccharidic headgroup. Static and dynamic, both po larized and depolarized, laser light scattering measurements show that the population of vesicles, of about 500 angstrom in diameter, is in equilibrium with a very small number of much larger non spherical obje cts, which can be schematized as discs with an average radius of 5 000 angstrom. Hydrophobic chains in the vesicle bilayer are likely to sho w a significative degree of interdigitation. Discs are found to disapp ear completely when a second amphiphile, GM1, with the same hydrophobi c part and a much larger saccharidic headgroup is added. Spontaneous v esicle formation is associated to the small rigidity of the gangliosid e bilayer which may derive from the large mismatch in the lateral dime nsion of the polar heads and hydrocarbon chains.