SECM measurement of the fast electron transfer dynamics between Au381+ nanoparticles and aqueous redox species at a liquid/liquid interface

Quantitative measurements are reported of the rate of interfacial electron transfers (ET) between gold monolayer protected clusters (Au MPCs) dissolved in 1,2-dichloroethane and aqueous redox species. Scanning electrochemical microscopy (SECM) current-distance approach curves were used to obtain the heterogeneous rate constant of ET between organic soluble Au-38 clusters and an aqueous IrCl62- oxidant. The Au cluster cores, protected with a shell of phenylethylthiolate ligands, are sufficiently small (d similar to 1.1 nm) to exhibit molecule-like redox activity. The evaluation of the ET rate constant at the nonpolarizable liquid/liquid interface was accomplished using an approach previously developed for bimolecular ET reactions between conventional redox entities. The dependences of the effective heterogeneous rate constant, k(f), on the concentration of the aqueous redox mediator and reaction driving force were found to be in agreement with theoretical expectations.