Electrochemical Screening of Redox Mediators for Electrochemical Regeneration of NADH

We report the electrochemical cofactor regeneration for electroenzymatic reduction as a promising alternative to the enzymatic recycling due to the avoidance of couple products. In the mediated electron transfer reaction appropriate redox mediators for the cofactor reduction are necessary. We have synthesized different redox mediators-based on rhodium complexes-and have screened their electrochemical performance at different pH values and concentrations. Suitable mediators have been tested in the presence of the cofactor NAD+ and then additionally in the presence of D-sorbitol dehydrogenase (DSDH) from Rhodobacter sphaeroides. The electroenzymatically generated product was analyzed by HPLC. As result of the screening some mediator species were identified which enable an efficient electrochemical cofactor reduction.