Adsorption of cyanuric chloride-activated polyethylene glycol on liposomes

One method for obtaining sterically stabilized liposomes consists of mixing an excess of cyanuric chloride-activated polyethylene glycol 5000 (activated PEG) with liposomes bearing distearoylphosphatidylethanolamine. Quantitative analysis of activated PEG present in extruded liposomes suggested that it can be found grafted as well as coated on the liposomal surface. Penetration kinetics at constant area and surface activity have shown the ability of activated PEG to adsorb on liposomes. This suggests that the interaction between activated PEG and lipid is primarily hydrophobic, and the triazine group of activated PEG must be embedded in the lipid. Microelectrophoretic measurements are consistent with the process of adsorption observed: Incorporation of PEG reduces the corresponding zeta potentials, but the presence of PEG in the bulk increases them in absolute terms. An experimental value lying between such extremes indicates that PEG is adsorbed.