SURFACE-POTENTIAL OF LIPID MONOLAYERS WITH GRAFTED POLYETHYLENE GLYCOLS

In this study we investigated the origin and the magnitude of surface potentials of monolayers composed of lipids to which polyethylene glyc ol(PEG) is covalently bonded. Under the first set of experimental cond itions we measured the surface potential of lipid monolayers composed of different lipids. In the second set we added free PEG to the subpha se of the monolayers. In the third series we investigated the variatio n of the polyethylene glycol moieties covalently attached to the lipid s. The experimental data allowed the separation of different contribut ions to the surface potential originating from the hydrocarbon side ch ain, the surface charge, and PEG. For lipid monolayers in the gas phas e up to a surface pressure of 10 mN/m, the contribution of the PEG dom inated the surface potential and the surface pressure while near the c ollapse point the lipids gave the main contribution to both parameters . The results showed a good correlation to recent measurements of the surface potentials of liposomes formed from the same lipids. (C) 1994 Academic Press, Inc.