Electrochemical regeneration of oxidised nicotinamide cofactors in a scalable reactor

An efficient and scalable NAD(P)+ regeneration system to promote alcohol dehydrogenase-catalysed oxidation reactions is reported. Indirect electrochemical oxidation of NADH was established with 2,2′-azino-bis-(3 ethyl-benzo-thiazoline-6-sulfonic acid) (ABTS), being the most efficient mediator amongst the candidates screened. ABTS exhibited very high catalytic performance of 1200 catalytic turnovers per hour. In a three-dimensional electrochemical cell with a high working electrode surface area of 24 m2 and optimised concentrations of substrate, enzyme, cofactor and mediator, TTNs of 1860 for the mediator and of 93 for the cofactor were measured. Besides, a maximum STY of 1.4 g l−1 h−1 was determined. Here we show the highest TTN ever reported for a mediated NAD+ regeneration in an electro-enzymatic process. The use of the three-dimensional electrochemical reactor led to an 8-fold improvement of the STY compared to a published system, based on a two-dimensional cell.