Electrochemical regeneration of NAD in a plug‐flow reactor

Abstract

Electrochemical regeneration of NAD was performed at a laboratory preparative scale to illustrate both the efficiency and intrinsic simplicity of the electrochemical method. A powerful plug-flow reactor was realized with a flow through graphite felt electrode, the ratio of the effective area of electrode/volume of reactor increased to 380 cm(2)/cm(3). This graphite-felt electrode was able to oxidize NADH coenzyme at a very low overvoltage. On the example of the gluconic acid production catalyzed by glucose dehydrogenase, current as high as 0.1 A was obtained in experience where enzymatic activity was the main limitation. In confirmation of our previous work, the results show that the yield of NADH electrochemical oxidation is better than 99.95%.

Can the combination of electrochemical regeneration of NAD+, selectivity of L-?-amino-acid dehydrogenase, and reductive amination of ?-keto-acid be applied to the inversion of configuration of a L-?-amino-acid?

“…It is now well established that the electrochemical regeneration of enzymatically active NAD + can be achieved quite efficiently either directly at a carbon anode (Bonnefoy et al, 1988;Fassouane et al, 1990;Laval et al, 1987) or mediated by polyoxometalates (Essaadi et al, 1994;Keita et al, 1995;Keita et al, 1996;Sadakane and Steckhan, 1998;Steckhan, 1994), quinonoid compounds (Blankespoor and Miller, 1984;Tse and Kuwana, 1978;Persson et al, 1985) and their transition-metal complexes (Hilt et al, 1997a,b), or by enzymatic systems (Cosnier et al, 1997;Palmore et al, 1998). The direct electrochemical regeneration can be performed with a yield exceeding 99.99%, but requires an anodic potential that may be too positive for the selective oxidation of some substrates (Bonnefoy et al, 1988).…”

“…In practical reactors the sole driving force provided by the electrochemical regeneration of the coenzyme is not sufficient to draw the oxidation toward completion even when the configuration of the system is optimized (Fassouane et al, 1990;Lortie et al, 1992). The only effective method is to remove the product as it forms (Lee and Whitesides, 1985).…”

“…The key steps of the reaction scheme involved in Figure 1 are the electrochemical regeneration of NAD + which is irreversible and rapid, provided that the anode potential is positive enough (Biade et al, 1992;Bonnefoy et al, 1988;Fassouane et al, 1990;Laval et al, 1987), the reversible enzymatically catalyzed reaction, the reversible formation of the imine, and the irreversible electrochemical reduction of the latter (Anne et al, 1994). The flow of two moles of electrons through the system provokes the transformation of half a mole of L-alanine into the same quantity of D-alanine while one mole of NAD + undergoes a complete redox cycle.…”

Immobilized redox mediators for electrochemical NAD(P)+ regeneration

“…The electrodeposition occurred via cyclic voltammetric procedure and rendered an electrode with good electrocatalytic activity towards NADH oxidation. Another technique to lower the overpotential for NADH oxidation is the oxidative pretreatment of the anode (Anne et al 1999;Biade et al 1992;Fassouane et al 1990;Obón et al 1997), which results in the formation of quinoid structures and adsorbed activated oxygen species (Hollmann and Schmid 2004). The 4-PAA/PEDOT/GC electrode had an overpotential for NADH oxidation about 400 mV lower than the bare electrode (Balamurugan and Chen 2008).…”

Application of an Electrochemical NAD+ Recycling System Involving a String-Like Carbon Fiber to an Enzyme Reactor

“…In this case, the research goals were selection of a working electrode material, oxidation of NADH without any mediators, reduction of the voltage of NADH oxidation, and the maintenance of the stability of the enzymes and NAD þ . The following materials are known as materials for working electrodes: carbon graphite and felt derived from graphite, [1][2][3][4][5][6] felt and paper derived from a carbon fiber (Toray, Tokyo, Japan), 7,8) glassy carbon, 9) and platinum. 10) Carbon fiber derivatives such as paper and felt, and carbon graphite felt, are known to show comparatively low oxidation voltages as to NADH.…”