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Reversed-phase HPLC chromatographic separations of Au monolayer protected clusters (MPCs) in the size range 1-2 nm (diameter) are detected electrochemically (ECLC) on the basis of double layer charging of the metal-like nanoparticles by the detector electrode. Discrete double-layer charging peaks are detected for the nanoparticles with resolution similar to that of the photodiode array detector. The ECLC experiment further seeks not solely to detect the nanoparticle peaks, but to estimate the nanoparticle sizes from the electrochemical responses. Hydrodynamic current--potential curves of nanoparticles eluted in different peaks were obtained by repeating chromatographic separations at different working electrode potentials; the [E.sub.1/2] separations between the voltammetric waves give estimates of cluster capacitance and, thus, size. Other approaches to core size determination are discussed, including determination based upon relative values of optical absorbance and current for each eluted peak. The data show that, at least for alkanethiolate MPCs, the elution order on the HPLC column employed is small clusters first and that there are significant differences in reversed-phase chromatographic retention times for clusters with apparently very similar core sizes over the range of 1-2-nm diameter.

New liquid ionic materials based on DNA salts of polyether-tailed cations are reported to have electrochemical properties.

We describe the use of the Taylor dispersion method to determine the diffusion coefficients of monolayer protected clusters (MPCs). The MPCs have nanometer Au cores ([approximately] 1- 5 nm diameter) coated with a passivating, self-assembled monolayer of thiolate ligands ([approximately]40-600). The results are found to agree with electrochemically measured diffusion coefficients, validating both approaches for measuring nanoparticle diffusivities. Taylor diffusion coefficients are used to calculate MPC hydrodynamic diameters under the sticking and the slip boundary conditions of the Stokes-Einstein equation, which are compared to the overall MPC diameter-estimated as the core diameter (measured by TEM) plus the length (2L) of two fully extended ligands. Better agreement between calculated and experimental hydrodynamic diameters of alkanethiolate-coated MPCs in organic solvents are obtained using slip boundary conditions, implying free draining of solvent through the outer portion of the extended chains. The hard-sphere (sticking) version of the Stokes-Einstein relation predicts unrealistically small hydrodynamic diameters. Similar but less clear-cut results are obtained for tiopronin-coated MPC ions in aqueous media.

This report describes how the electrochemical double-layer capacitances of nanometer-sized alkanethiolate monolayer-protected Au clusters (MPCs) dissolved in electrolyte solution depend on the alkanethiolate chain length (C4 to C16). The double-layer capacitances of individual MPCs ([C.sub.CLU]) are sufficiently small (sub-attoFarad, aF) that their metal core potentials change by > 0.1 V increments for single electron transfers at the electrode/solution interface. Thus, the current peaks observed are termed 'quantized double layer charging peaks', and their spacing on the potential axis varies with [C.sub.CLU]. Differential pulse voltammetric measurements of [C.sub.CLU] in solutions of core-size-fractionated (i.e., monodisperse) MPCs are compared to a simple theoretical model, which considers the capacitance as governed by the thickness of a dielectric material (the monolayer, whose chain length is varied) between concentric spheres of conductors (the Au core and the electrolyte solution). The experimental results fit the simple model remarkably well. The prominent differential pulse voltammetric charging peaks additionally establish this method, along with high-resolution transmission electron microscopy and laser ionization-desorption mass spectrometry, as a tool for evaluating the degree of monodispersity of MPC preparations. We additionally report on a new tactic for the preparation of monodisperse MPCs with hexanethiolate monolayers.

Electrogenerated anthraquinone radical anions that are ligated to monolayer-protected gold clusters were used to reduce 1,1-dinitrocyclohexane. The clusters were prepared by place-exchange of a fraction of the cluster's original octanethiolate ligands with 1-(1,3-dithiapropyl)anthracene-9,10-dione. The electrocatalytic efficiency was found to be larger for cluster-bound anthraquinone. The improvement in catalytic efficiency was due to the smaller diffusion coefficient of cluster-bound anthraquinone compared to that of the monomer, resulting in spatial compression of the reaction zone next to the electrode.

A viscous molten salt [Ru(bby)2(bpy(CO2MePEG350)2)](ClO4)2] that glasses at ca. -5 degrees celsius resulted from the attachment of two polyethylene glycol tails to ruthenium tris(bipyridine) through ester links on the 4,4'-positions of one of the bypyridine ligands. RuIII and RuI reaction led to electrochemically chemiluminescent emission with an efficiency of 0.2% photons/electron.

Electrochemical oxidation of highly oriented pyrolytic graphite (HOPG) electrodes in KN[O.sub.3] electrolyte solution at a carbon submonolayer level was shown in a previous paper to produce raised, bubblelike features, giving the appearance of shallow blisters. The blisters were established to be hollow, with a top surface of intact HOPG lattice and an inner one of graphitic oxide. This paper explores the relationship of the intercalating properties of the electrolyte anion to the blister formation on HOPG. Cyclic voltammetry, atomic force microscopy, optical microscopy, and in situ atomic force microscopy/electrochemistry results are presented. Surface blister formation is observed to occur in 1 M LiCl[O.sub.4], 1 M [(N[H.sub.4]).sub.2]S[O.sub.4], 1 M HN[O.sub.3], and 1 M [H.sub.2]S[O.sub.4] aqueous electrolytes as a result of potential scans (+1.50 to +1.90 V vs SSCE, depending on the electrolyte) that pass a few carbon monolayers of charge or less. Blister formation on HOPG in 1 M KOH electrolyte is observable but at significantly higher levels of oxidative charge, whereas blisters were not observed in 1 M [K.sub.2]HP[O.sub.4] and 1 M [H.sub.3]P[O.sub.4] electrolytes. These results are consistent with literature Raman intercalation data that indicate phosphate does not readily intercalate into HOPG, supporting a model in which blister formation reflects electrolyte anion intercalation followed by subsurface gas evolution.

Oxidation of the first fractional carbon monolayer on highly oriented pyrolytic graphite (HOPG) electrodes is topographically manifested by the formation of well-defined surface blisters consisting of a solid skin covering a hollow interior. Atomic force microscopy (AFM), optical microscopy (OM), and scanning electron microscopy (SEM) show that the surface blisters formed by application of potentials from +1.5 to +1.63 V vs SSCE in 1.0 m [KNO.sub.3] are from 20 to 1000 nm high and from 0.5 to 50 [micro]m at the base. Surface analyses by AFM, X-ray microprobe, and Auger electron spectroscopy indicate that the outermost layer of the blister skin is essentially intact HOPG lattice (at the atomic scale) while the interior of the blister top contains a layer of graphite oxide (EGO). We propose that, following intercalation of electrolyte and water into the HOPG, blisters form as a result of electrolytic gas evolution at subsurface active sites (e.g., crystallite grain boundaries) with accompanying parallel electrolytic formation of EGO. The HOPG electrode kinetics of the Fe-[[(CN).sub.6].sup.3-/4-] couple are only slightly enhanced by oxidation at +1.62 V, relative to the large changes in k[degrees] caused by oxidation at +1.99 V, consistent with AFM images that show modest overall changes in the HOPG surface lattice in the former case and extensive lattice damage with exposure of edge plane sites in the latter case., The topographical manifestations of the oxidation of the first fractional carbon monolayer of basal plane highly oriented pyrolytic graphite electrode surfaces was analyzed. The formation of well-defined blisters in the electrode was characterized by atomic force, optical, scanning electron Auger electron microscopies and surface and energy-dispersive x-ray microanalyses. Results indicate that these blisters were formed due to electrolytic gas evolution at the subsurface active sites.

The electrochemistry of metal nanoparticles, single nanoelectrodes and nanopores are discussed. The developments in the fabrication and characterization of single nanopores, nanoelectrodes and nanoparticles are described.

The synthesis and characterization of two slightly different [Au.sub.13] cluster molecules, [Au.sub.13][[PPh.sub.3].sub.4][[S[(C[H.sub.2]).sub.11]C[H.sub.3]].sub.2][Cl.sub.2] and [Au.sub.13][[PPh.sub.3].sub.4][[S[(C[H.sub.2]).sub.11]C[H.sub.3]].sub.4], are described. The electrochemical and spectroscopic properties of the two [Au.sub.13] cluster molecules are compared with those of a secondary synthetic product and the characterization of sub-nanometer clusters have shown how these [Au.sub.13] clusters display structure not present in the bulk material.

Issues concerning the synthesis and examination of polyether, semisolid, MPEG-based redox molten salts of mixed-valent ruthenium complexes, using electrochemical measurements, and their electron-transfer chemistry are discussed. Analysis of the optically-driven electron transfer process indicates that ion association contributes thermal electron-transfer energy barriers in these redox melts.