Nicotinamide adenine dinucleotide (NAD⁺) reduction enabled by an atomically precise Au-Ag alloy nanocluster

The redox property of the ultrasmall coinage nanoclusters (with several to tens of Au/Ag atoms) has elucidated the electron-transfer capacity of nanoclusters, and has been successfully utilized in a variety of redox conversions (such as from CO₂ to CO). Nevertheless, their biological applications are mainly restricted by the scarcity of atomically precise, water-soluble metal nanoclusters, and the limited application (mainly on the decomposition of H₂O₂ in these days). Herein, mercaptosuccinic acid (MSA) protected ultrasmall alloy AuAg nanoclusters were prepared, and the main product was determined [Au₃Ag₅(MSA)₃]⁻ by electrospray ionization mass spectrometry (ESI-MS). The clusters can not only mediate the decomposition of H₂O₂ to generate hydroxyl radicals, but is also able to mediate the reduction of nicotinamide adenine dinucleotide (NAD) to its reduced form of NADH. This is the first time that the atomically precise metal nanoclusters were used to mediate the coenzyme reduction. The preliminary mechanistic insights imply the reaction to be driven by the hydrogen bonding between the carboxylic groups (on the surface of MSA) and the amino N–H bonds (on NAD). In this context, the presence of the carboxylic groups, the sub-nanometer size regime (~ 1 nm), and the synergistic effect of the Au-Ag clusters are pre-requisite to the NAD reduction.