Indophenol andO-Quinone Derivatives Immobilized on Zirconium Phosphate for NADH Electro-oxidation

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 MARCEL DEKKER, INC. • 270 MADISON AVENUE • NEW YORK, NY 10016buffers, 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 2þ 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 Â 10 6 M À1 s À1 .

NADH Electrooxidation Using Bis(1,10-phenanthroline-5,6-dione)(2,2′-bipyridine)ruthenium(II)-Exchanged Zirconium Phosphate Modified Carbon Paste Electrodes

“…Several authors have demonstrated the use of this material for the construction of NADH biosensors. Mediators previously immobilized in α-ZrP are phenoxazines, phenothiazines, phenazines, fluorenones and flavines [15,[37][38][39][40]. These authors did not use enzymes in their studies nor provided X-ray powder diffraction (XRPD) evidence of the mediator intercalation into the layered material.…”

“…However, the electrochemical oxidation of NADH (or NADPH) requires a high overvoltage and suffers from side chemical reactions [18,19]. The use of redox mediators has been demonstrated to substantially overcome these limitations, particularly in dehydrogenase sensors [4,15,20]. Ideal mediators should exhibit chemical and electrochemical reversibility, stability under physiological conditions, a fast electron exchange reaction with the coenzymes, and a suitable redox potential, usually between −0.2 to 0 V vs. SCE to avoid interferences in biological determinations [5,18,21].…”

“…These sensors are attractive for several reasons [10][11][12][13][14][15][16][17]: 1) complex organic molecules can be determined with the convenience, speed and ease that characterize amperometric measurements; 2) biocatalysts permit reactions to occur under mild conditions of temperature, pH and minimal substrate concentrations; 3) the sensor response is analyte dependent as dictated by the specificity of most enzyme reactions; and 4) the measured signal is inherently amplified by the enzyme catalytic cycle.…”

Immobilized redox mediators for electrochemical NAD(P)+ regeneration

“…Several authors have demonstrated the use of α-zirconium phosphate for the construction of NADH biosensors. Mediators that have been immobilized in α-zirconium phosphate are Nile blue (Malinauskas et al 2000), toluidine blue (Malinauskas et al 2000), Meldola's Blue (Ladiu et al 2007;Munteanu et al 2001), methylene green (Munteanu et al 2001), 2,4,7-trinitro-9-fluorenone (Munteanu et al 2002), and 2,6-dichlorophenolindophenol (Dicu et al 2003). Cyclic voltammetric investigations of Meldola's Blue, methylene green, and riboflavin immobilized on α-zirconium phosphate performed in buffered solutions at different pHs have also been performed (Munteanu et al 2001).…”

“…Furthermore, for a catalytic system, the pH independency is helpful due to different pH optima of the enzymes and limited buffer capacity of the solution. The addition of Ca 2+ to a buffered solution of 2,6-dichlorophenolindophenol adsorbed on α-zirconium phosphate in the presence of NADH was shown to increase the oxidation current (Dicu et al 2003). The kinetic parameters obtained for Meldola's Blue adsorbed via zirconium phosphate on a GC paste electrode were adversely influenced by increased surface coverage (Γ) (Ladiu et al 2007).…”