INVESTIGATION OF THE ADSORPTION OF DIOLEOYL-L-ALPHA-PHOSPHATIDIC ACIDMONOLAYER AND BILAYER FROM VESICLE SOLUTION ONTO POLYETHYLENIMINE-COVERED SUBSTRATES

The formation of monolayers and bilayers of dioleoyl-L-alpha-phosphati dic acid from solutions of small unilamellar vesicles onto polyethylen imine-treated substrates was investigated by means of small angle X-ra y scattering and X-ray photoelectron spectroscopy. The formation of mo nolayers could be verified after an adsorption time of 5 min, on remov al of the substrates from the vesicle solution and washing with water. No adsorption of dioleoyl-L-alpha-phosphatidic acid takes place when the substrates used have not been pretreated with polyethylenimine. Th is suggests that the interaction of the charges of polyethylenimine wi th the phosphatidic acid headgroups is the driving force for the adsor ption. Further experiments show that immersion of the supported bilaye rs in polyethylenimine solution again leads to dried films with layer thicknesses of approximately twice the values of the supported monolay ers. From this observation the formation of supported bilayers of lipi d/polyelectrolyte complexes is derived.