Monolayer-protected metal nanoparticles are commonly prepared by a two-phase synthesis in which metal complexes in aqueous solution are reduced in the presence of a nonpolar solvent that contains an alkanethiol. This approach, often termed the Brust-Schiffrin method, is extended to the preparation of polyoxometalate-protected nanoparticles in aqueous solution. Initially, hexanethiol-protected gold nanoparticles were prepared in toluene. After purifying and fractionating to obtain monodisperse nanoparticles, transfer of the metal center to an aqueous solution was accomplished by ligand exchange involving replacement of the alkanethiolate with a polyoxometalate (POM), phosphomolybate or phosphotungstate. Evidence for phase transfer of the gold nanoparticle core without a change is size will be presented. These ca. 5-nm anionic moieties are amenable to electrostatic assembly of multilayers on electrodes such as indium tin oxide modified with a monolayer of 3-aminopropyl triethoxysilane. The ability of the POM to catalyze electrochemical reductions is enhanced by the gold nanoparticle core. This synergism will be demonstrated for the reduction of bromate and of dioxygen. Fabrication of multilayered composites of POM-protected nanoparticles and conducting polymers also will be described. For example, alternating layers of anionic POMs and aniline, which subsequently forms a conducting polymer, increases the population of catalytic centers; communication between centers is promoted by the conducting polymer. Control of the quantity of deposition of the conducting polymer by assembly of polyaniline nanoparticles rather than the aniline precursor will be discussed.

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