Properties of mixed vesicles of lecithin: cholesterol up to a 1:2 molar ratio.

The cholesterol solubilizing capacity of lecithin vesicles was studied and some physicochemical properties of the resulting mixed vesicles were investigated. The maximum association of ultrasonicated cholesterol and lecithin was found to be a cholesterol/lecithin molar ratio of 2:1, with a limiting concentration of colloidal lipid of approximately 34 mg/ml. The 2:1 dispersions were found to be rather stable with no change in cholesterol/lecithin ratios for long periods. The mixed 2:1 cholesterol/lecithin vesicles were separated by Sepharose 4 B chromatography to obtain homogeneous preparations. The homogeneity was further tested by analytical ultracentrifugation and electron microscopy. Light-scattering measurements showed an increase in particle weight with increasing cholesterol proportion. 1H-and 13C-NMR studies demonstrated an additional broadening, especially of chain resonances, when going from a cholesterol/lecithin molar ratio of 1:1 to 2:1.