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 (activat ed PEG) with liposomes bearing distearoylphosphatidylethanolamine. Quantita tive analysis of activated PEG present in extruded liposomes suggested that it can be found grafted as well as coated on the liposomal surface. Penetr ation kinetics at constant area and surface activity have shown the ability of activated PEG to adsorb on liposomes. This suggests that the interactio n between activated PEG and lipid is primarily hydrophobic, and the triazin e group of activated PEG must be embedded in the lipid. Microelectrophoreti c measurements are consistent with the process of adsorption observed: Inco rporation of PEG reduces the corresponding zeta potentials, but the presenc e of PEG in the bulk increases them in absolute terms. An experimental valu e lying between such extremes indicates that PEG is adsorbed. (C) 2001 Else vier Science B.V. All rights reserved.