CUBIC PHASES OF GANGLIOSIDES IN WATER - POSSIBLE ROLE OF THE CONFORMATIONAL BISTABILITY OF THE HEADGROUP

An accurate X-ray scattering study of the self-association properties in water of the ganglioside GM1, a biological amphiphile similar to ph ospholipids but with an oligosaccharide headgroup, is described. The p hase diagram displays a large cubic region, for concentrations between 31% and 55% by weight, enclosed by isotropic micellar and lamellar ph ases. The peculiar feature of the GM1 molecule to present a conformati onal bistability, recently observed in ganglioside micelles, can be we ll recognized in the cubic phase region, suggesting that GM1-water beh aves like a pseudoternary system, with an additional degree of freedom , automatically readjusting the mole fraction of the two conformers in order to optimize the molecular packing.