Oxidation electroenzymatic

Fig. 4. Electroenzymatic oxidation of / -D-glucose with direct electrochemical NAD+ regeneration (GDH = glucose dehydrogenase)...

Fig. 6. Schematic representation for the ADH-catalyzed electroenzymatic oxidation of 2-hexene-l-ol and 2-butanol with indirect electrochemical NAD+ regeneration using (3,4,7,8-tetramethyl-l.lO-phenanthroline) iron(II/III) [Fe(tmphen)3] as redox catalyst...

Fig. 12. Electroenzymatic oxidation of p-cresol under catalysis by PCMH in. long-time batch electrolysis under formation of p-hydroxy benzylalcohol (alcohol) and p-b. .roxy benzaldehyde (aldehyde) (PCMH 16 U = 5.6 nmol PEG-20000 ferrocene 3 0.51 mmr - 9.45 pmol ferrocene starting concentration of p-cresol 41.25 mM = 0.66 mmol additions o. substrate after 4140 min (0,0925 mmol), 5590 min (0.0784 mmol), 6630 min (0.184 mmol), 11253 min (0.371 mmol), in 10 ml tris/HCl-buffer of pH 7.6 divided cell Sigraflex-anode 26 cm2)...

Electroenzymatic reactions are not only important in the development of ampero-metric biosensors. They can also be very valuable for organic synthesis. The enantio- and diasteroselectivity of the redox enzymes can be used effectively for the synthesis of enantiomerically pure compounds, as, for example, in the enantioselective reduction of prochiral carbonyl compounds, or in the enantio-selective, distereoselective, or enantiomer differentiating oxidation of chiral, achiral, or mes< -polyols. The introduction of hydroxy groups into aliphatic and aromatic compounds can be just as interesting. In addition, the regioselectivity of the oxidation of a certain hydroxy function in a polyol by an enzymatic oxidation can be extremely valuable, thus avoiding a sometimes complicated protection-deprotection strategy. 

Ruinatscha R, Hollrigl V et al (2006) Productivity of selective electroenzymatic reduction and oxidation reactions theoretical and practical considerations. Adv Synth Catal 348 2015-2026... 

The electrical potential and/or current required for electroenzymatic treatment have been shown to be lower than those needed in electrochemical treatment, which are not economically viable for large-scale. Electroenzymatic oxidation by peroxidases was proposed for the oxidation of veratryl alcohol by LiP [40], Then, electroenzymatic reactors have been used for the treatment of petrochemical wastewater [91], dyes, and textile wastewater [90, 92, 118] and phenol streams [93] utilizing peroxidase immobilized onto inorganic porous Celite beads or directly onto the electrode. The integration of a second electrochemical reactor, which generated hypochlorite in the presence of sodium chloride, has been used for indirect oxidation of the reaction products of the electroenzymatic treatment [91]. 

Lee K, Moon SH (2003) Electroenzymatic oxidation of veratryl alcohol by lignin peroxidase. J Biotechnol 102 261-268... 

Lutz, S., Steckhan, E. and Liese, A. (2004) First asymmetric electroenzymatic oxidation catalyzed by peroxidase. Electrochemistry Communications, 6, 583-587. 

Association between enzymatic and electrochemical reactions has provided efficient tools not only for analytical but also for synthetic purposes. In the latter field, the possibilities of enzymatic electrocatalysis, e.g., the coupling of glucose oxidation (catalyzed either by glucose oxidase or glucose dehydrogenase) to the electrochemical regeneration of a co-substrate (benzoquinone or NAD+) have been demonstrated [171, 172]. An electroenzymatic reactor has also been developed ]172] to demonstrate how the enzyme-electrode association can be used to produce biochemicals on a laboratory scale. 

Scheme 11. Idealized sketch showing the electroen matic oxidation of L-lactate at gold modified electrode surfaces, (a) Lactate dehydrogenase bound to CB-terminated alkylthiol SAMs prepared by covalent attachment of CB to 3-mercaptopropionic acid SAM derivatized with 1,4-diaminobutane. The electroenzymatic oxidation of lactate is observed only in the presence of soluble coenzyme (NAD" ") and a redox mediator (phenazine methosulfate) [215]. (b) Lactate deh3tdrogenase bound to NAD-terminated alkylthiol SAMs prepared by covalent attachment of Af -(2-aminoethyl)-NAD to a cystamine SAM derivatized with pjrrroloquinoline quinone. The reconstituted enzyme is electrically wired to the electrode surface via two NAD" -binding pockets involved in the affinity-binding surface reaction [242].

Similarly, the pyruvate (oxidase) dehydrogenase complex (PYOX) can be activated directly by electrogenerated methyl viologen radical cations (MV" ) as mediator. Thus, the naturally PYOX-catalyzed oxidative decarboxylation of pyruvic acid in the presence of coenzyme A (HSCoA) to give acetylcoenzyme A (acetyl-SCoA) (see section on oxidases) can be reversed. In this way, electroenzymatic reductive carboxylation of acetyl-SCoA is made possible (Fig. 15). 

Figure 21. Electroenzymatic oxidation of w e o-diols to give enantiomerically pure lactones with horse liver alcohol dehydrogenase (HLADH) and PDMe" as redox catalysts at pH 7.8 and 150mV vs. Ag/AgCl reference [125].

The enzyme / -ethylphenol methylene hydroxylase (EPMH), which is very similar to PCMH, can also be obtained from a special Pseudomonas putida strain. This enzyme catalyzes the oxidation of /7-alkyphenols with alkyl chains from C2 to Cg to the optically active / -hydroxybenzylic alcohols. This enzyme was used in the same way as PCMH for continuous electroenzymatic oxidation of / -ethylphenol in the electrochemical enzyme membrane reactor with l,w-bisferrocenyl-PEG 20,000 (MW 20,000) as high-molecular-weight water-soluble mediator according to Fig. 25. During a 5-day experiment using a 16-mM concentration of / -ethylphenol, we obtained a turnover of the starting material of more than 90% to yield the (/ )- -(4 -hydroxyphenyl)ethanol with 93% optical purity and 99% enantiomeric excess (glc at a -CD-phase) at a residence time of 3 h. The (5 )-enan-tiomer was obtained by electroenzymatic oxidation using PCMH as production enzyme. 

Figure 25. Principle of the electroenzymatic oxidation of / -ethylphenol catalyzed by EPMH to give (/ )- -(4 -hydroxyphenyl)ethanol in an electrochemical enzyme membrane reactor.

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