INFLUENCE OF MEMBRANE-COMPOSITION ON THE INTRAVESICULAR PRECIPITATION OF NANOPHASE GOLD PARTICLES

Nanometer-sized gold crystallites were precipitated within multilamellar egg yolk phosphatidylcholine (PC) vesicles by incubation of lipid dispersions with aqueous HAuCl4. In situ reduction to Au(0) occurred rapidly in the presence of the lipid molecules. The vesicles and crystallites were characterized by transmission electron microscopy of air-dried stained and unstained samples, and of fixed and sectioned material. Intravesicular crystallites were spherical in morphology, had smaller diameters (mean = 4.1 nm), and were less aggregated as compared with Au crystals formed in the extravesicular phase (mean diameter = 25.1 nm). The influence of changes in the membrane composition on crystal nucleation and growth was investigated by the addition of secondary lipids to the PC vesicles. Incorporation of stearylamine resulted in a marked increase in the number of intravesicular Au(0) crystallites, particularly within the interlamellar regions, suggesting that the positively charged amine headgroups provide an energetically favorable site for Au(III) reduction and Au(0) nucleation. In contrast, only limited intravesicular crystallization occurred in PC vesicles containing negatively charged lipids such as phosphatidylserine, phosphatidylglycerol, or phosphatidic acid. © 1993 by Academic Press, Inc.