Intermolecular Interactions of Lithocholic Acid Derivatives with Phospholipid as Bilayer Membrane

Three single chain lithocholic acid derivatives with a steroidal moiety in the center of the hydrocarbon chain and two head groups at both ends of the chain were synthesized and characterized. Due to their high compatibility with phospholipids, they can be incorporated homogeneously into the phospholipid bilayer membrane. The resulting mixed vesicles showed high stability against aggregation by monitoring the turbidity change in the vesicle suspensions. The entire membrane-spanning packing thus locates the steroidal moiety at the center of the bilayer. The interaction of the steroidal moiety with lipid molecules at the center of the bilayer resulted in higher mobility of lipid molecules below the T_c of the host phospholipid membrane as clarified by temperature-dependent ¹H NMR, fluorescence depolarization anisotropy, and differential scanning calorimetry (DSC). The results were compared with those of cholesterol, whose steroidal moiety is located near the surface of the membrane.