INDUCTION OF A HEXAGONAL PHASE IN PHOSPHOLIPID-SURFACTANT BILAYERS

The possibility of modifying the curvature of lipid bilayers by mixing them with additives is demonstrated and the evolution of geometrical parameters with composition is discussed. X-ray diffraction patterns o f the POPC/C12EO2/(H2O)-H-2 system were observed as a function of the relative humidity. The formation of an unexpected hexagonal phase indi cates peculiar behaviour in these mixtures. The cylinder radius of thi s phase is considerably smaller than previously observed in cubic phas es. A discussion of the head group interactions is presented. We have also been able to show that the uptake of water by the L-beta gel phas e is higher as a single phase than in the L-beta+H-II two phase region . The water content is important for the stabilization of H-II phase a nd determination of its characteristic dimensions. However, it is argu ed that the interaction between the surfactant and the lipid is the ke y factor for its formation and that the EO2 head groups displace water from the inner parts of the polar region of the mesogenic units.