Abstract
The direct electrochemical reduction of nicotinamide adenine dinucleotide (NAD+) results in various products, complicating the regeneration of the crucial 1,4-NADH cofactor for enzymatic reactions. Previous research primarily focused on steady-state polarization to examine potential impacts on product selectivity. However, this study explores the influence of dynamic conditions on the selectivity of NAD+ reduction products by comparing two dynamic profiles with steady-state conditions. Our findings reveal that the main products, including 1,4-NADH, several dimers, and ADP-ribose, remained consistent across all conditions. A minor by-product, 1,6-NADH, was also identified. The product distribution varied depending on the experimental conditions (steady state vs. dynamic) and the concentration of NAD+, with higher concentrations and overpotentials promoting dimerization. The optimal yield of 1,4-NADH was achieved under steady-state conditions with low overpotential and NAD+ concentrations. While dynamic conditions enhanced the 1,4-NADH yield at shorter reaction times, they also resulted in a significant amount of unidentified products. Furthermore, this study assessed the potential of using pulsed electrochemical regeneration of 1,4-NADH with enoate reductase (XenB) for cyclohexenone reduction.
Keywords:
chemoselectivity; cofactors; direct electrochemical 1,4-NADH synthesis; dynamic operation; enoate reductase.