Electrochemical Regeneration of NAD P H

Nevertheless, the great potential of electrochemical regeneration, especially in terms of environmentally benign reaction schemes, makes more intensive research in this area highly desirable  

Product/ee-value (%) Scale Catalysts (loading) Yield [%) TN (NAD(P)) Reference 

HLADH ADH from horse liver UfADH ADH from Lactobacillus brevis BFR benzoyl formate  

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Organometallics such as rhodium complex were also used for electrochemical regeneration of NAD(P)H from electrode (Figure 8.10) [7bj. 

For enzymatic reductions with NAD(P)H-dependent enzymes, the electrochemical regeneration of NAD(P)H always has to be performed by indirect electrochemical methods. Direct electrochemical reduction, which requires high overpotentials, in all cases leads to varying amounts of enzymatically inactive NAD-dimers generated due to the one-electron transfer reaction. One rather complex attempt to circumvent this problem is the combination of the NAD+ reduction by electrogenerated and regenerated potassium amalgam with the electrochemical reoxidation of the enzymatically inactive species, mainly NAD dimers, back to NAD+ [51]. If one-electron... 

Electrochemical regeneration of NAD(P)H represents another interesting method 134 361. The system involves electron transfer from the electrode to the electron mediator such as methyl viologen or acetophenone etc., then to the NAD(P)+ (which is catalyzed by an electrocatalyst such as ferredoxin-NADP reductase or alcohol dehydrogenase, etc.) [34l Other methods involve the direct reduction of NAD on the electrode[35). Both one-enzyme systems and two-enzyme systems have been reported. 

Because the direct electrochemical oxidation of NAD(P)H has to take place at an anode potential of +900 mV vs. NHE or more, only rather oxidation-stable substrates can be transformed without loss of selectivity, thus limiting the applicability of this method. The electron transfer between NADH and the anode may be accelerated by the use of a mediator. At the same time, electrode fouling, which is often observed in the anodic oxidation of NADH, can be prevented. Synthetic applications have been described for the oxidation of 2-hexene-1 -ol and 2-butanol to 2-hexenal and 2-butanone catalyzed by yeast alcohol dehydrogenase (YADH) and the alcohol dehydrogenase from Thermoanaerobium brockii (TBADH), respectively, with indirect electrochemical regeneration of NAD" and NADP", respectively, using the tris(3,4,7,8-tetramethyl-l,10-phenan-throline) iron(II/III) complex as redox catalyst at an anode potential of 850 mV vs. NHE [106]. Under batch electrolysis conditions using a carbon felt anode, the turnover number per hour was 40. The current efficiency reached between 90 and 95%. 

Catalytic Oxidation of NAD(P)H A Continuously Improved Selection of Suitable ROMs This research is triggered hy at least two reasons (1) the importance of NAD(P)H/NAD(P)- - redox couples in biological systems is known, as is known the dependence of oxidation mechanisms on the oxidants [14, 82, 172-174] (2) the possibility of developing amperometric biosensors for NAD(P)+-dependent dehydrogenases. As a consequence, much attention is devoted to the regeneration of these coenzymes in their reduced or oxidized forms for their application in biosensors or in enzymatic synthesis [180]. Here, we are concerned with electrochemical regeneration [181]. 

Further research for useful mediators led to the anthracycline antibiotic adria-mycin which serves as a novel mediator for the FNR or diaphorase (DP) catalyzed electrochemical reduction of NAD(P)+ [107]. This regeneration system has been satisfactory combined with NAD(P)H-dependent enzymatic reactions. The NADP+-dependent FNR/adriamycin system was coupled with GluDH. GluDH was entrapped together with FNR on the electrode surface. NADPH was efficiently... 

Cofactor Regeneration, Electrochemical, Fig. 3 ECE mechanism of NAD(P)H oxidation SET = single electron transfer [5]... 

Phenanthrolindiones are often used as mediators because of their high stability. To reduce the oxidation potential for the electrochemical regeneration and to enhance the hydride transfer from NAD(P)H, the electron density of the o-chinoid structure should be decreased [92]. This can be done by complexation with a... 

Several aspects have to be considered in order to regenerate NAD(P)H by an indirect electrochemical procedure without the application of a second regeneration enzyme The active redox catalyst should transfer two electrons in one step or a hydride ion. At potentials more negative than —0.9 V vs SCE, NAD+ dimers will be formed, so the electrochemical activation of the catalyst should be possible at potentials less negative than —0.9 V. To prevent low chemoselectivity and low enantioselectivity, the active form of the catalyst should not transfer the electrons or the hydride ion directly to the substrate but to NAD(P)+. Furthermore, only active 1,4-NAD(P)H should be formed [90]. 

Figure 10. Application of VAPOR enzymes for the indirect electrochemical NAD(P)H regeneration.

To be able to regenerate NAD(P)H by an indirect electrochemical procedure without the application of a second regeneration enzyme system, the redox catalyst must fulfil four conditions ... 

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