Self-aggregation properties of gangliosides, glycosidic surfactants of biological origin

A comparative study of the aggregation properties of a class of glycosidic surfactants, all having the same hydrophobic part but different saccharidic headgroups, is presented. Although the surfactants, gangliosides, are of biological origin, the reported data can be of general use. Gangliosides are double-tail surfactant like phospholipids, but have a ramified oligosaccharide chain headgroup. They may form either micelles or bilayers depending on the length and conformation of the oligosaccharide chain. For long chains, micelles are formed with a large aggregation number and a long lifetime (many hours), while vesicles are formed for shell sugar chains. Their critical micelle concentration is very low of the order of 10(-8) M, and the micellar dimension is independent of the ionic strength of the solution, even if gangliosides are ionic surfactants due to the presence of sialic acids. Steric effects of the headgroups are very important. For instance the ganglioside GM3 forms vesicles spontaneously in solution with a low bending rigidity of the bilayer. Data are interpreted in terms of the existing geometrical models of self-assembly.