Glucose electrochemical oxidation

Many dehydrogenase enzymes catalyze oxidation/reduction reactions with the aid of nicotinamide cofactors. The electrochemical oxidation of nicotinamide adeniiw dinucleotide, NADH, has been studied in depthThe direct oxidation of NADH has been used to determine concentration of ethanol i s-isv, i62) lactate 157,160,162,163) pyTuvate 1 ), glucose-6-phosphate lactate dehydrogenase 159,161) alanine The direct oxidation often entails such complications as electrode surface pretreatment, interferences due to electrode operation at very positive potentials, and electrode fouling due to adsorption. Subsequent reaction of the NADH with peroxidase allows quantitation via the well established Clark electrode. 

FIGURE 5.7. Effect of changing the cosubstrate and the pH on the kinetics of an homogeneous redox enzyme reaction as exemplified by the electrochemical oxidation of glucose by glucose oxidase mediated by one-electron redox cosubstrates, ferricinium methanol ( ), + ferricinium carboxylate ( ), and (dimethylammonio)ferricinium ( ). Variation of the rate constant, k3, with pH. Ionic strength, 0.1 M temperature 25°C. Adapted from Figure 3 in reference 11, with permission from the American Chemical Society. 

The detection step involves electrochemical oxidation at a nickel electrode. This electrode has been applied to measurements of glucose (4), ethanol (5), amines, and amino acids (6,7). The reaction mechanism involves a catalytic higher oxide of nickel. The electrolyte solution consists of 0.1 M sodium hydroxide containing 10-4 M nickel as suspended nickel hydroxide to ensure stability of the electrode process. The flow-injection technique offers the advantages of convenience and speed in solution handling and ready maintenance of the active electrode surface. 

The presence of glucose, fructose, galactose, arabinose and citric, malic and tartaric acid did not produce interference on the quantification of gluconic acid. Only ascorbic acid yielded an amperometric response under the working conditions, due to the electrochemical oxidation of this compound at the applied potential. Nevertheless, the content of gluconic acid in honey samples is remarkably higher than the possible content of ascorbic acid. Consequently, no significant interference should be expected in the analysis of the proposed real samples. 

Indeed, the mathematical form of the mixed-potential concept (Bockris, 1954) has been applied to a number of chemical processes which, it has been shown, in fact, consist of two partnered surface electrochemical processes (Spiro, 1984). Thus, energy conversion processes at the surface of mitochondrial cells may involve the electrochemical oxidation of glucose as the anodic reaction and the electrochemical reduction of oxygen as the cathodic (Gutmann, 1985). 

Koga, T. and Taniguchi, I., Electrochemical oxidation of glucose to glucarate using TEMPO as a mediator in an alkaline solution. Electrochemistry 2004, 72 (12), 858-860. 

Carbonaceous substrates (graphite and glassy carbon) are generally preferred because of their mechanical, chemical, and electrochemical properties. Excellent results are also obtained by chemically modified platinum (154,156,179) and tin(IV) oxide electrodes (155). For example, glucose oxidase has been successfully immobilized by cross-linking the enzyme with BSA and GA onto an electrochemically oxidized platinum surface, with silanization using 3-amino-propyltriethoxysilane ... 

It also was found that the direction of the photobiocatalytic switch of the nitrospiropyran-FAD-reconstituted enzyme is controlled by the electrical properties of the electron transfer mediator. With ferrocene dicarboxylic acid as a diffusional electron transfer mediator, the enzyme in the nitrospiropyran-FAD state (10a) was found to correspond to the OFF state bio-catalyst, while the protonated nitromerocyanine state of the enzyme (10b) exhibits ON behavior. In the presence of the protonated 1-[1-(dimethyl-amino )ethyl]ferrocene, the direction of the photobioelectrocatalytic switch is reversed. The nitrospiropyran-enzyme state (10a) is activated toward the electrocatalyzed ox idation of glucose, while the protonated nitromerocyanine enzyme state (10b) is switched OFF, and is inactive for the electrochemical oxidation of glucose. This control of the photoswitch direction of the photoisomerizable reconstituted enzyme was attributed to electrostatic interactions between the diffusional electron mediator and the photoisomefizable unit... 

Some details are given by Merck in Ref. 112. The electrochemical oxidation is performed in alkaline solution using nickel or nickel oxide electrodes [113]. Hydrogen evolved at the cathode can be used for the hydrogenation of D-glucose to D-sorbitol, the first step in the vitamin C synthesis by the Reichstein route. Obviously, Merck doesn t use electrodes with high specific areas but prefers to stop the electrolysis at a conversion rate of 90%. The oxidation is completed with sodium hypochlorite solution. 

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