L-ALPHA-PHASE SEPARATION IN PHOSPHATIDYLCHOLINE-WATER SYSTEMS INDUCEDBY ALKALI CHLORIDES

The effects of alkali chlorides on phosphatidylcholine-water bilayer s ystems in the L-alpha-phase were investigated by using small- and wide -angle X-ray scattering. The ternary system LICl-POPC-H2O under isothe rmal 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 Brag g diffraction peaks into discrete components indicates a phase separat ion into different lamellar liquid crystalline (smectic A) phases. It is also shown that in saturated distearoyl phosphatidylcholine and in egg phosphatidylcholine, alkali chlorides induce L-alpha-phase separat ion. The number and repeat distance of the coexisting lamellar phases depend on the nature and concentration of the alkali chloride, the con centration of the phosphatidylcholine, and the degree of the acyl chai n unsaturation. (C) 1998 Elsevier Science B.V. All rights reserved.