Electrocatalytic oxidation of NADH

Figure 3.13 — Set-up for the electrocatalytic oxidation of NADH catalysed by the reduced form of diaphorase (Dp). Dp (red) and Dp (ox) reduced and oxidized form of diaphorase. (Reproduced from [88] with permission of the Royal Society of Chemistry).

E. Maestre, I. Katakis and E. Dominguez, Amperometric flow-injection determination of sucrose with a mediated tri-enzyme electrode based on sucrose phosphorylase and electrocatalytic oxidation of NADH, Biosens. Bioelectron., 16(1-2) (2001) 61-68. 

An alternative biosensor system has been developed by Hart et al. [44] which involves the use of the NAD+-dependent GDH enzyme. The first step of the reaction scheme involves the enzymatic reduction of NAD+ to NADH, which is bought about by the action of GDH on glucose. The analytical signal arises from the electrocatalytic oxidation of NADH back to NAD+ in the presence of the electrocatalyst Meldola s Blue (MB), at a potential of only 0Y. Biosensors utilising this mediator have been reviewed elsewhere [1,17]. Razumiene et al. [45] employed a similar system using both GDH and alcohol dehydrogenase with the cofactor pyrroloquinoline quinone (PQQ), the oxidation of which was mediated by a ferrocene derivative. 

Some derivatives with mediating properties are suitable to form chemically modified electrodes (CMEs) with catalytic properties for NADH oxidation (55). Various attempts have been tried with different classes of mediators to immobilize the mediator onto solid electrodes or in carbon paste electrodes since the first deliberately made CME for electrocatalytic oxidation of NADH was described by Tse and Kuwana in 1978 (56), see Table I. They and others (67-72) based their CMEs on immobilized ortho-quinone derivatives. However, these CMEs were rapidly inactivated in the presence of NADH, probably because of side reactions in the catalytic process (72). For some other immobilized mediators one major reaction route could be proposed as the CME turned out to be quite stable in the presence of NADH. The catalytic reaction sequence comprizes two steps, one chemical between NADH and the immobilized mediator (reaction (6)) and one electrochemical between the mediator and the electrode (reaction (7)). The sequence is given below for the simplest case ... 

Figure 4. Basic structures of mediators for electrocatalytic oxidation of NADH.

Some of the structures reported from this laboratory for making CMEs for electrocatalytic oxidation of NADH are summarized in Figure 5. We have found that a positively charged paraphenylene-diimine is the best basic catalytic structure (55,83,84-87,89,91,92). When it is incorporated as a part of a phenoxazine or a phenothiazine (see Figure 5) some very beneficial properties are added to the mediator. The E° values are decreased with some 300 to 400 mV compared with the free paraphenylenediimine structure (57,58,102) and they strongly adsorb on graphite electrodes to form CMEs allowing NADH to be electrocatalytically oxidized well below 0 mV (55,83,84-87,89,91,92). 

In another example, a mixed monolayer composed of a photoisomerizabie component and an electrochemical catalyst was applied to switch the electrocatalytic properties of a modified eleetrode between ON and OFF states. A Au-electrode surface functionalized with a nitrospiropyran mono-layer and PQQ moieties incorporated into the monolayer was applied to control the electrocatalytic oxidation of 1,4-dihydri-P-nicotinamide adenine dinucleotide (NADH) by light. The positively charged nitromerocyanine-state interface resulted in the repulsion of Ca cations, which are promoters for the NADH oxidation by the PQQ, thus resulting in the inhibition of the electrocatalytic process. In the nitrospiropyran state, the monolayer does not prevent the association of the PQQ catalyst and promoter thus it provides efficient electrocatalytic oxidation of NADH. Similar outcomes have been achieved using a combination of the photo- and thermal effects resulting... 

Due to high biocompability and large surface are of cobalt oxide nanoparticles it can be used for immobilization of other biomolecules. Flavin adenine FAD is a flavoprotein coenzyme that plays an important biological role in many oxidoreductase processes and biochemical reactions. The immobilized FAD onto different electrode surfaces provides a basis for fabrication of sensors, biosensors, enzymatic reactors and biomedical devices. The electrocatalytic oxidation of NADH on the surface of graphite electrode modified with immobilization of FAD was investigated [276], Recently we used cyclic voltammetry as simple technique for cobalt-oxide nanoparticles formation and immobilization flavin adenine dinucleotide (FAD) [277], Repeated cyclic voltammograms of GC/ CoOx nanoparticles modified electrode in buffer solution containing FAD is shown in Fig.37A. 

Fang, C. and Zhon, Y. (2001). The electrochemical characteristics of Cgo-glutathione modified Au electrode and the electrocatalytic oxidation of NADH, Electroanalysis, 13, 949-54. 

Figure 14-9. Cyclic voltammogram of a graphite electrode modified with P-naphthoyl Nile Blue, a) buffer (pH 8.0) b) after addition of NADH (10 mM). The increase in the anodic current is attributed to electrocatalytic oxidation of NADH at the mediator-modified electrode. - SOO to +300 mV vs. SCE 5 mV s" 0.1 M phosphate buffer (pH 8.0) with 0.5 M NaCl graphite disk electrode, 6.4 mm diameter.

The electrocatalytic oxidation of NADH in 0.1 M NaNOj by the self-assembly of MNC is illustrated in Fig. 10-29. A dramatic enhancement of the anodic peak current consistent with a very strong electrocatalytic effect is observed in the presence of NADH (Fig. 10-29b). Also no cathodic peak current is observed for the SAM of MNC in the presence of NADH, which indicates that the electroproduced Ni(III) complex is effectively consumed in the catalysis. 

The electrocatalytic oxidation of NADH has also been carried out in the presence of other supporting electrolytes such as Na2S04 and phosphate buffer solutions (Table 10-4). Although of the Ni(III/II) surface redox wave shifts toward the less positive potential when the supporting electrolyte is changed from NaNOs to Na2S04, for the oxidation of NADH becomes more positive. 

Table 10-4. Formal potentials of SAM of MNC and anodic peak potentials, current densities and apparent rate constants (A at) for the electrocatalytic oxidation of NADH at SAM of 1 in different supporting electrolytes. ...

D.D. Schlereth, E. Katz and H.L. Schmidt, Surface-modified gold-electrodes for electrocatalytic oxidation of NADH based on the immobilization of pheno-xazine and phenothiazine-derivatives on self-assenbled monolayers. Electroanalysis, 1995, 7, 46-54. 

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Persson B, Gorton L. A comparative study of some 3,7-diaminophenoxazine derivatives and related compounds for electrocatalytic oxidation of NADH. J Electroanal Chem 1990 292 115-138. 

Pariente F, Tobalina F, Moreno G, Hernandez L, Lorenzo E, Abruna HD. Mechanistic studies of the electrocatalytic oxidation of NADH and ascorbate at glassy carbon modified with electrodeposited films derived from 3,4-dihydroxybenzaldehyde. Anal Chem 1997 69 4065 075. 

Silber A, Hampp N, Schuhmann W. Poly(methylene blue)-modified thick-film gold electrodes for the electrocatalytic oxidation of NADH and their application in glucose biosensors. Biosens Bioelectron 1996 11 215-223. 

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