Lalpha-phase separation in phosphatidylcholine-water systems induced by alkali chlorides

The effects of alkali chlorides on phosphatidylcholine-water bilayer systems in the Lalpha-phase were investigated by using small- and wide-angle X-ray scattering. The ternary system LiCl-POPC-H2O under isothermal conditions has shown that above Li+/POPC molar ratios of 0.1 and a lipid concentration above 5% (w/w), a splitting of the lamellar Bragg diffraction peaks into discrete components indicates a phase separation into different lamellar liquid crystalline (smectic A) phases. It is also shown that in saturated distearoyl phosphatidylcholine and in egg phosphatidylcholine, alkali chlorides induce Lalpha-phase separation. The number and repeat distance of the coexisting lamellar phases depend on the nature and concentration of the alkali chloride, the concentration of the phosphatidylcholine, and the degree of the acyl chain unsaturation.