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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.

Electrons are transported within polymeric films of alkanethiolate monolayer-protected Au clusters (MPCs) by electron hopping (self-exchange) between the metal cores. The surrounding monolayers, the molecular linkers that generate the network polymer film, or both, presumably serve as tunneling bridges in the electron transfers. This paper introduces a steady-state electrochemical method for measuring electron hopping rates in solvent-wetted and swollen, ionically conductive MPC films. The films are network polymer films of nanoparticles, coated on a rotated disk electrode that is contacted by a solution of a redox species (decamethylferrocene, Cp*Fe). Controlling the electrode potential such that the film mediates oxidation of the redox probe can force control of the overall current onto the rate of electron hopping within the film, which is characterized as the apparent electron diffusion coefficient [D.sub.E]. [D.sub.E] is translated into an apparent electron hopping rate [k.sub.ET] by a cubic lattice model. The experiment is applied to MPC network polymer films linked by [alpha], [omega]-alkanedithiolates and by metal ion-carboxylate connections. We evaluate the dependencies of apparent hopping rate on Cp*Fe concentration, film thickness, electrode potential relative to the Cp*Fe formal potential, film-swelling solvent, and temperature. The apparent hopping rates are in the [10.sup.4]-[10.sup.5] [s.sup.-1] range, which is slower than those for the same kind of MPC films, but in a dry (nonswollen) state measured by electronic conductivities.

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.

Cyclic voltammetry and electromechanical methods were used to study the reduction of the antimalarial agent Artemisinin (ART) in N,N-dimethylformamide (DMF). The standard potential of the dissociative reduction of ART is found to be -0.89 V versus SCE in DMF, which is ca. 0.8 V more positive than the irreversible direct reduction resulting from cyclic voltammetric measurements. Moreover, the value of the dissociative reduction of ART can be used to estimate the O-O bond dissociation energy.

The synthesis, characterization, and properties of a series of gold nanoclusters protected by thiolated peptides based on the alpha-aminoisobutyric acid (Aib) unit are described. The infrared (IR) and NMR spectra has shown that in the monolayer the peptides are involved in both intra- and interligand C=O...H-N hydrogen bonds.

The synthesis of ~2 nm NO-releasing gold nanoparticles is an important step toward the development of a NO-delivery system that bridges small-molecule diazeniumdiolates and diazeniumdiolate-modified fumed silica particles. Further functionalization of the nanoparticles with receptor molecules to enable specific antibody-antigen or ligand-receptor interactions may allow for the targeting of specific tissues or cells.

The electrochemical and spectroscopic properties of a well-characterized, synthetically accessible, 1.1 nm diam Au nanoparticle, Au38(PhC2S)24 are discussed. A study on the voltammetry of the Au38 nanoparticles in CH2Cl2 reveals a 1.62 V energy correction of ca. 0.29 V.

The homogeneous and heterogeneous reductions of the endoperoxides 9,10-epidioxyanthracene (DPA-O2) and 9,10-dimethyl-9,10-epidioxyanthracene (DMA-O2) are investigated. The initial electron transfer (ET) reduction DPA-O2 and DMA-O2 follows a dissociative mechanism with fragmentation of the O-O bond to yield a distonic radical anion.

Gold nanoparticles are the focus of numerous investigations because of their optical, electronic, and chemical properties. The first results for the electron-transfer dynamics of the smallest, most molecular, member (8 kDa) of this transition are provided.

Endoperoxides are significant chemical intermediates in the activity of several substances. The values of the standard reduction potentials (Eodiss) for the two bicyclic endoperoxides, ascaridole (ASC) and dihydroascaridole (DASC) in aprotic media, are reported. The kinetics of their homogenous reduction was examined, as a driving force of electron transfer (ET).

Electrochemical methods are used to investigate the dynamics of the concerted dissociative reduction of di-tert-butyl peroxide (DTBP), dicumyl peroxide (DCP) and di-n-butyl peroxide (DNBP). The role of steric effects on the kinetics of reduction is examined by comparing DTBP with the heterogeneous reduction of DNBP and the homogeneous reduction of DCP. The overall results suggest that the concerted dissociative reduction of the three dialkyl peroxides is nonadiabatic.

Sequential injections of single electrons (or holes) into the cores of Au140 hexanethiolate monolayer-protected clusters (MPCs) occur at measurably different electrochemical potentials owing to the extremely small (subattofarad) values of the single MPC capacitance (CMPC) of the nanoparticle. The potential increment for each sequential injection is ΔV = e/CMPC. The dependence of ΔV on the concentration of supporting electrolyte (from 1 to 100 mM), measured using square wave voltammetry, is shown to be caused, primarily, by changes in the diffuse double layer component (CDIFFUSE) of CMPC. The dependence of CDIFFUSE on rcore, the radius of the nanoparticle, is considered. Additionally, significant changes in the magnitude of the compact double layer component (CCOMPACT, equivalent to the Stern layer) of CCMP were induced by adding hydrophobic solvent components such as hexane or dodecane or by introducing hydrophobic electrolyte ions (tetrabutyl-, tetrahexyl-, and tetraoctylaminonium, 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. [ABSTRACT FROM AUTHOR]

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 doublelayer 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 E1/2 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. [ABSTRACT FROM AUTHOR]

Monolayer-protected nanoparticles (MPNs) with average core sizes of 1.7- (small), 2.2- (medium) and 4.5-nm (large) diameter have been prepared and functionalized with a variety of aryl ketone substrates, namely, 11-mercaptoundecaphenone (1), 1-(4-hexyl-phenyl)-11-mercaptoundecanone (2), 1-[4-(11-mercaptoundecyl)phenyl]hexanone (3), or 1-[4-(11-mercaptoundecyl)phenyl]undecanone (4). Upon irradiation in benzene solution, the aryl ketone-modified MPNs undergo the Norrish type II photoreaction and yield alkene- or acetophenone-modified MPNs exclusively, with no evidence for the generation of cyclobutanol. The extent of the photoreaction for the entire series of aryl ketones is dependent on the size of the MPN core. For 11-mercaptoundecaphenone, the reaction proceeds nearly to completion on the smallest MPN cores (99 +/- 1%) but occurs to a much lesser extent on medium (85 +/- 5%) and large cores (66 +/- 6%). The differences in the extents of reaction are rationalized by the decreased reactivity of substrates on terrace regions, which become increasingly larger with the core size. In lending support to this hypothesis, the edge and vertex sites of medium-sized MPNs were selectively populated with an aryl ketone probe and shown to react quantitatively, whereas selective population of the terrace sites on the same-sized MPNs results in a much lower extent of reaction. Together, these results indicate differences in reactivity of monolayer substrates on terrace versus edge/vertex sites of MPNs. The differences in reactivity with site will play a role in the design of modified MPNs for applications.