Micelle-Dependent Spontaneous Formation of Gold(I)\nin Nanodendritic Chloride-Bridged Particles with Catalytic Activity\nfor Cyclization of Alkynylanilines in an Aqueous Environment

A proline-based\nengineered amphiphile featuring a thiourea functional\ngroup has been synthesized for the purpose of controlled reduction\nof Au(III) to Au(I) with subsequent stabilization of the resulting\nnanomaterial. This study elucidates the significant role played by\nthe designer amphiphile, alongside chloride ions, in imparting a dendritic\nmorphology to the final nanocatalyst. Such a morphology is pivotal\nfor the catalytic activity of Au(I), as demonstrated in the cyclization\nreaction of alkynylanilines, conducted in water as a benign reaction\nmedium. The structural characterization of the nanomaterial revealed\nintriguing associations between dendritic nanocatalysts and nanomicelles,\nas observed through cryogenic transmission electron microscopy. Spectroscopic\nanalyses, including X-ray photoelectron and X-ray absorption spectroscopy,\ncorroborate the presence of Au in the +1 oxidation state within the\ndendritic nanomaterial. The metal–amphiphile binding is further\nsupported by an X-ray absorption fine structure analysis. Cyclic voltammetry\nanalysis confirms the amphiphile-mediated reduction of Au(III) to\nAu(I). Significantly, the dendritic morphology is inaccessible when\n bromide ions are employed, whose greater nucleophilicity disrupts\nthe bridging linkages formed by the chloride counterpart. Under these\nconditions, the catalytic activity is adversely affected.