Electrocatalytic oxidation of reduced nicotinamide adenine dinucleotide (NADH) at a chlorogenic acid modified glassy carbon electrode

Department of Chemistry, Faculty of Science, University of Tehran, Tehran, Iran; Electroanalytical Chemistry Laboratory, Faculty of Chemistry, University of Tabriz, Tabriz, Iran
Journal of Electroanalytical Chemistry (Impact Factor: 2.58). 03/1999; DOI: 10.1016/S0022-0728(98)00459-8

ABSTRACT The redox response of chlorogenic acid solution at an inactivated glassy carbon electrode was investigated and an ECE mechanism was proposed for the electrode process. It has been shown that the oxidation of chlorogenic acid at an activated glassy carbon electrode leads to the formation of a deposited layer of about 4.5×10−10 mol cm−2 at the surface of the electrode. Cyclic voltammetry was used for the deposition process and the resulting modified electrode retains the activity of the quinone/hydroquinone group anticipated for a surface-immobilized redox couple. The properties of the electrodeposited films, during preparation under different conditions, and the stability of the deposited film were also examined. The pH dependence of the redox activity of these films was found to be 57 mV per pH unit, which is very close to the anticipated Nernstian dependence of 59 mV per pH unit. The modified electrode exhibits potent and persistent electrocatalysis for NADH oxidation in phosphate buffer solution (pH 7.0) with a diminution of the overpotential of about 430 mV and an increase in peak current. The electrocatalytic current increases linearly with NADH concentration from 0.1 to 1.0 mM. The apparent electron transfer rate constant, ks, and the heterogeneous rate constant for electrooxidation of NADH, kh, were also determined using cyclic voltammetry and rotating disk electrode voltammetry, respectively.

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    ABSTRACT: The electrocatalytic properties for NADH oxidation of five organic dyes, two indophenol derivatives (2,6-dichlorophenolindophenol and indophenol) and three o-quinone derivatives (phenanthrenequinone, pyrroloquinoline-quinone, and 1,2-naphthoquinone) were compared when adsorbed on zirconium phosphate entrapped in carbon paste. The electrochemical behavior of the immobilized dyes was investigated with cyclic voltammetry, performed in different aqueous buffers, at different potential scan rates and pH values. The electrocatalytic efficiency for NADH oxidation was evaluated from cyclic voltammetry, and the second order electrocatalytic rate constant was calculated from rotating disk electrode experiments, at various concentrations of NADH and pH values. These studies indicate that the mechanism of such electro-oxidation proceeds via the formation of an intermediate complex. A positive effect with the addition of Ca cations to the solution was observed and the reaction rate for NADH oxidation increased. The highest second order rate constant was obtained for 2,6-dichlorophenolindophenol and found to be 4.6 × 10 M s.
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