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

Unilamellar vesicles are observed to form spontaneously in dilute water solutions of the ganglioside GM3, which is a double-tailed biological amphiphile with a saccharidic headgroup. Static and dynamic, both polarized 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 objects, which can be schematized as discs with an average radius of 5 000 angstrom. Hydrophobic chains in the vesicle bilayer are likely to show a significative degree of interdigitation. Discs are found to disappear completely when a second amphiphile, GM1, with the same hydrophobic part and a much larger saccharidic headgroup is added. Spontaneous vesicle formation is associated to the small rigidity of the ganglioside bilayer which may derive from the large mismatch in the lateral dimension of the polar heads and hydrocarbon chains.