ESR STUDY OF ORDER AND DYNAMICS IN LECITHIN LIPOSOMES WITH HIGH CHOLESTEROL CONTENT

Previous studies have shown that increasing amounts of cholesterol in phosphatidyl choline liposomes (involving cholesterol/lecithin ratios up to 1), produce an increase in order and a decrease in mobility of the phospholipids in the bilayer. The present work focuses on the order and dynamics of the phospholipids in soybean and egg yolk liposomes with cholesterol/lecithin (chol/lec) ratios as high as 2. The influence of cholesterol on the order parameter and correlation times of 5-, 12- and 16-doxyl stearic acid probes, is analyzed for both types of liposomes. The order parameter increases continuously with the increase of the amount of cholesterol although the correlation time at first increases, then it levels off at a chol/lec ratio of 1, and thereafter shows a small, gradual decrease up to a ratio of 2. A statistical model of cholesterol substitution on the lecithin lattice was employed to explain the correlation time results.