CHOLESTERYL-PULLULAN AND CHOLESTERYL-AMYLOPECTIN INTERACTIONS WITH EGG PHOSPHATIDYLCHOLINE MONOLAYERS

The extent of adsorption of cholesteryl-pullulan and cholesteryl-amylopectin at air-water interface was assessed from the surface pressure measurements at constant area. It was found that areas per adsorbed cholesterol derivative of pullulan and amylopectin are 0.40 and 0.19 nm2, respectively. These small areas indicate that sugar moieties of both polysaccharide derivatives are completely immersed in the aqueous phase. The surface potential data strongly suggest that the cholesteryl moieties of adsorbed cholesteryl derivative of pullulan are stretched toward the air phase, but lay flat, exposing lateral CH3 groups to the interface, in the case of a cholesteryl derivative of amylopectin. Surface pressure and surface potential isotherms of egg-phosphatidylcholine monolayers were shown to be greatly modified in the presence of cholesterol-substituted polysaccharides in the aqueous subphase. The results reveal the ability of both polysaccharide derivatives to penetrate the lipid monolayer. However, this effect is superior for cholesteryl-amylopectin, which interacts strongly with the lipid even at very high surface coverages. cholesteryl-amylopectin also compensates lipid surface potential to a higher extent than cholesteryl-pullulan. This would explain why liposomes coated with cholesteryl-amylopectin exhibit lower stability relative to those coated with a cholesterol derivative of pullulan. © 1991 Academic Press, Inc.