Direct Electron Transfer to a Metalloenzyme Redox Center Coordinated to a Monolayer-Protected Cluster

A strategy for establishing electrical contact to the metal center of a redox metalloenzyme, galactose oxidase (GOase), by coordination of a linker attached to a monolayer-protected gold cluster is presented. The cluster−enzyme hybrid system was first prepared in solution and characterized by high-angle annular dark-field scanning transmission electron microscopy. Electrochemical communication between a gold electrode and GOase was achieved by first modifying the electrode surface with a biphenyl dithiol self-assembled monolayer followed by reaction with gold clusters capped with thioctic acid. GOase was then immobilized by replacement of the H2O molecule at the CuII exogenous site by coordination of a carboxylate-terminated gold cluster. This chemical attachment ensured electrical contact between the redox center and the electrode, leading to direct mediatorless electron transfer to the protein. Hybrid systems can find applications in biosensors and biofuel cells and for studying electrochemically the catalytic mechanism of reactions for which free radicals and electron-transfer reactions are involved. The present results can be extended to other metalloenzymes

Substrate Structural Effects on the Synthesis and Electrochemical Properties of Platinum Nanoparticles on Highly Oriented Pyrolytic Graphite

Platinum nanoparticles have been prepared by potentiostatic multipulse electrodeposition with controlled nucleation and growth on freshly cleaved and electrochemically oxidized highly oriented pyrolytic graphite. The influence of the applied potential sequence on the size distribution was investigated. For short electrolysis times, the deposition of nanoparticles takes place via a progressive nucleation mechanism. A narrow size distribution was obtained by controlling independently the nucleation and growth steps, and particles with heights between 52 and 1.4 nm could be prepared by altering the pulse parameters. Anodic oxidation of the substrate had a large influence on the particle size, resulting in the preparation of particles 1.4 nm in height. XPS demonstrated that Pt particles of small size were readily oxidized. The rate of electrochemical methanol oxidation showed a dependence on the particle size, and no oxidation of methanol could be observed for the smaller sizes investigated

Oriented Immobilization of <i>Desulfovibrio </i><i>gi</i><i>gas</i> Hydrogenase onto Carbon Electrodes by Covalent Bonds for Nonmediated Oxidation of H₂

The orientation of hydrogenase bound covalently to a pyrolytic graphite edge electrode modified with a 4-aminophenyl monolayer can be modulated via electrostatic interactions during the immobilization step. At low ionic strength and when the amino groups of the electrode surface are mostly protonated, the hydrogenase is immobilized with the negatively charged region that surrounds its 4Fe4S cluster nearer to the protein surface facing the electrode. This allows direct electron transfer between the immobilized hydrogenase and the electrode, which is observed by the strong catalytic currents measured in the presence of the H2 substrate. Therefore, a very stable enzymatic electrode is produced that catalyzes nonmediated H2 oxidation

Synthesis of ω-Hydroxy Hexathiolate-Protected Subnanometric Gold Clusters

The synthesis of ω-hydroxy hexathiolate-protected subnanometric gold clusters is described. Quantitative high-angle annular dark-field scanning transmission electron microscopy has been employed to determine atomic composition. The smallest particles observed contain 13 ± 2 Au atoms; all others contained multiples of this particle size. The UV−vis spectra show the bands of discrete electronic transitions for this core size. Chemical analyses indicate a composition of Au13(SC6OH)8 for the clusters. The role of the ligand shell in determining the core size is highlighted