Electrochemical Preparation of VPtCl[sub 6] Film and Its Electrocatalytic Properties with NAD[sup +] and Sulfur Oxoanions

Abstract

A modified electrode with vanadium hexachloroplatinate ͑VPtCl 6 ͒ film has been fabricated directly from the mixing of V 2+ and PtCl 6 2− ions, and its electrochemical behavior was investigated. The deposition of a VPtCl 6 film occurred when Pt IV Cl 6 2− was electrochemically reduced to Pt II Cl 6 2− and V 3+ to V 2+ . The electrochemical quartz crystal microbalance ͑EQCM͒, ultraviolet-visible absorption spectroscopy, stopped-flow, chronoamperometry, and cyclic voltammetry techniques were used to study the deposition and growth mechanism of the above film. In the EQCM studies, the reversibility of the vanadium ͑II/III͒ hexachloroplatinate film during cycling and the corresponding frequency change was found to be good, and the V 2+ ion exchange obviously occurred in the redox couple. For the surface morphological analysis, the film was further electrochemically deposited on a transparent semiconductor indium tin oxide ͑ITO͒ electrode for scanning electron microscopy and atomic force microscopy studies. It was found that the deposited VPtCl 6 film formed as a film with platinum and vanadium particles on ITO. To validate the electroanalytical properties, a VPtCl 6 -modified glassy carbon electrode was applied for the electrocatalytic reduction of the NAD + ͑␤-Nicotinamide adenine dinucleotide͒ and sulfur oxoanions, and the results showed a quite effective electrocatalytic reduction for the corresponding substances.Generally, the biochemical reactions that are catalyzed by redox enzymes such as oxidoreductases or dehydrogenases depend on the use of NAD͑H͒ as a cofactor that plays the role of the electron and hydrogen carrier. In the reduced form, NADH, the molecule transfers two electrons and a proton to a substrate in the presence of a suitable enzyme, resulting in the oxidation of NADH to ␤-Nicotinamide adenine dinucleotide ͑NAD + ͒. In the biomedical and industrial area, the NADH has important values. The enzymatically catalyzed electroreduction of NAD + has also attracted considerable attention for both biosensor development and large-scale applications. So, the reduction of NAD + to NADH has attracted significant scientific attention over the years. Chemically modified electrodes 1-3 and enzyme-mediated electrodes 4-6 have been proposed for NAD + reduction. A number of studies have been reported, and a large majority of these relies on an electron-mediator-assisted reduction mechanism. While enzymatic modification of an electrode surface can give hopeful results in the reduction of NAD + to enzymatically active 1, 4-NADH, this method results in a somewhat complex electrode system due to problems associated with the immobilization of an enzyme and electron mediator at the electrode surface, including loss of the enzyme activity and electron mediator leakage. Hence, there is a need to develop a simple electrode surface that would allow electrochemical reduction of NAD + . It is therefore desirable to design a modified electrode that would have a long-term stability and offer a high efficiency in the reduction of ...

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