The cubic phase of phosphatidylethanolamine film by small angle x-ray scattering

Using small angle x-ray scattering, we have investigated the effects of polyvinylpyrrolidone (PVP) and oleic acid (OA) on the structures of the cubic phase of 1,2-dielaidoyl-sn-glycero-3-phosphoethanolamine (DEPE) films. At lower PVP concentrations, DEPE–PVP mixed films existed in two cubic phases. With increasing PVP concentration in the DEPE–PVP mixed phase, a phase transition from Q229 (Im3m) to Q224 (Pn3m) occurred. The effect of addition of OA to a DEPE–PVP mixed phase was also determined using a certain fixed amount. At 0.5 mol% OA, the presence of low amounts of OA allows the DEPE–PVP–OA system to organize in a cubic Q229 phase. At 1.0 mol% OA, the presence of larger amounts of OA induces formation of coexisting Q229 and Q224 phases. At 1.5 mol% OA, the presence of even larger amounts of OA promotes formation of a cubic Q224 phase in the DEPE–PVP–OA mixture.