Mediated Electrosynthesis of Nanocomposites of Gold Nanoparticles with Cyclobis (paraquat-p-phenylene)

The result of cyclobis(paraquat-p-phenylene) (CBPQT(4+)) -mediated reduction of gold ions generated by anodic oxidation of metallic gold in MeCN (50% vol.)-H2O/0.05 M Bu4NCl medium in the absence and presence of such stabilizers as cetyltrimethylammonium chloride and polyvinylpyrrolidone is polydisperse aggregated composite nanoparticles with sizes ranging from several nm to 100 nm or more. The resulting AuNP@(CBPQT(4+))(n) nanocomposite is a gold nanoparticle encapsulated in a shell of macrocycle molecules. CBPQT(4+) is bound to the surface of the gold nanoparticle by donor-acceptor interactions between the electron-withdrawing viologen units and the electron-donating metal particle. Theoretical calculations suggest that the cavity of the bound macrocycle is not empty, but filled with 10-12 gold atoms. CBPQT(4+) presumably forms a monomolecular layer on the metal surface, and its excess amount is involved in the aggregation and sedimentation of the nanocomposites. The encapsulation of AuNPs in the macrocyclic shell is the main reason for the suppression of the metal catalytic activity in the test reaction of p-nitrophenol reduction with sodium borohydride.