Effects of solvents interacting favorably with hydrophilic segments of the membrane surface of phosphatidylcholine on their gel-phase membranes in water

We have investigated the effects of two kinds of solvents forming the lamellar liquid-crystalline (L(alpha)) phase in phosphatidylcholine (PC) membranes in neat condition, such as formamide and 1,3-propanediol, on phase behaviors of multilamellar vesicle (MLV) of DPPC (DPPC-MLV). These solvents induced the interdigitated gel (L(beta)I) phase in DPPC-MLV in excess water above their critical concentrations. Solubility measurement indicates that these solvents interact favorably with the hydrophilic segment of the PC membrane but interact unfavorably with the alkyl chains. Based on these results, we propose the mechanism of the induction of the L(beta)I phase by these solvents.