Effects of hydrostatic pressure on the monoolein-water system: An estimate of the energy function of the inverted Ia3d cubic phase

Synchrotron x-ray diffraction has been used to investigate the mesomorphism of a monoolein-water dispersion under hydrostatic pressure. The results show the existence of a new phase, probably with cubic symmetry, before the transition from the L to the Lc lamellar phase occurs. Changes of the lipid bilayer conformation are discussed and the total energy function for the inverted cubic Ia3d and the lamellar L mesophase is derived. An estimate of the energy necessary for packing the lipid hydrocarbon chains is given.