Supporting electrolyte and solvent effects on single-electron double layer capacitance charging of hexanethiolate-coated [Au.sub.140] nanoparticles

Sequential injections of single electrons (or holes) into the cores of [Au.sub.140] hexanethiolate monolayer-protected clusters (MPCs) occur at measurably different electrochemical potentials owing to the extremely small (subattofarad) values of the single MPC capacitance ([C.sub.MPC]) of the nanoparticle. The potential increment for each sequential injection is [DELTA]V = e/[C.sub.MPC]. The dependence of [DELTA]V on the concentration of supporting electrolyte (from 1 to 100 raM), measured using square wave voltammetry, is shown to be caused, primarily, by changes in the diffuse double layer component ([C.sub.DIFFUSE]) of [C.sub.MPC]. The dependence of [C.sub.DIFFUSE] on [r.sub.core], the radius of the nanoparticle, is considered. Additionally, significant changes in the magnitude of the compact double layer component ([C.sub.COMPACT], equivalent to the Stern layer) of [C.sub.MPC] were induced by adding hydrophobic solvent components such as hexane or dodecane or by introducing hydrophobic electrolyte ions (tetrabutyl-, tetrahexyl-, and tetraoctylammonium, perchlorate, and tetraphenylborate). These changes are interpreted as specific solvation and ion penetration of the hexanethiolate monolayer. For brevity we will refer to these phenomena as solvation/penetration phenomena.