Using electrons stored on quantized capacitors in electron transfer reactions

Monolayer-protected clusters (MPCs) of gold with a majority composition of [CH3(CH2)(6)S](50)Au-145 have been synthesized. Solutions of this material in a toluene-acetonitrile solvent, containing a supporting electrolyte, are shown to display quantized double layer capacitance charging in differential pulse voltammetry experiments. These solutions can also be electrolytically charged to controllable potentials, and the average number of electrons (or holes) stored on the metal-like MPC cores can be estimated from the pattern of single-electron quantized charging peaks. The charged solutions are stable for hours. The charged MPCs can also be isolated in dried form, and retain most of their charge upon redissolution. The electronic charge on the MPC cores can be employed to carry out redox reactions with electron acceptor and donor molecules, such as ethylferrocene and TCNQ. These reactions proceed in a predictable and quantifiable way. Charged MPCs also undergo electron transfer reactions when mixed with solutions of differently charged MPCs, and the potential of the resulting solutions is completely consistent with Nernstian predictions. In the use of double layer charges to carry out redox transformations, these experiments illustrate a more quantitative capability than-has been previously described.