Oxidation of β-Nicotinamide Adenine Dinucleotide (NADH) by Au Cluster and Nanoparticle Catalysts Aiming for Coenzyme Regeneration in Enzymatic Glucose Oxidation

Supported Au clusters and nanoparticles can oxidize the coenzyme, β-nicotinamide adenine dinucleotide (NADH), under ambient conditions using O2 as an oxidant. The activity for NADH oxidation depends on the size of Au particles and the acidity of support materials. Au particles that have a higher ratio of surface Au atoms gave higher NAD+ yield, and the terrace sites of Au particles would play a key role in NADH oxidation. Au atoms on the terrace sites of Au particles are more important than those of the Au–support perimeter interface. Additionally, acidic supports increase the H+ concentration in the vicinity of Au particles, which drastically improves the NAD+ yield. Au clusters (1.9 nm in diameter) deposited on Nb2O5 gave higher product yield than Au clusters deposited on basic and amphoteric metal oxides. In the combination reaction of Au catalysts and glucose dehydrogenase, supported Au clusters convert NADH to NAD+, which is consumed in the following enzymatic glucose oxidation. Combinations of Au catalysts and dehydrogenases are good candidates for novel enzyme–artificial hybrid catalysts for organic syntheses.