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 phospholipids but with an oligosaccharide headgroup, is described. The phase diagram displays a large cubic region, for concentrations between 31% and 55% by weight, enclosed by isotropic micellar and lamellar phases. The peculiar feature of the GM1 molecule to present a conformational bistability, recently observed in ganglioside micelles, can be well recognized in the cubic phase region, suggesting that GM1-water behaves 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.