Cofactor-independent photo-enzymatic reductions with water mediated by reductive graphene quantum dots.

Enzymatic reductions catalyzed by reductases generally depend on reduced nicotinamide cofactors as a hydride source. However, for industrial viability, it is more cost-effective to use water as the hydrogen source, bypassing the requirement for the cofactor. Here we report a hybrid photo-biocatalyst system based on infrared (IR) light and responsive reductive graphene quantum dots (rGQDs), for performing the direct transfer of hydrogen from water to prochiral substrates. The photo-biocatalyst, assembled from rGQDs and cross-linked aldo-keto reductase (AKR), mediates the synthesis of the pharmaceutical intermediate, (R)-1-[3,5-bis(trifluoromethyl)-phenyl] ethanol ((R)-3,5-BTPE), in 82% yield and >99.99% ee under IR illumination. Our photo-enzymatic systems can also be effectively used to drive the enzymatic reduction of imines and alkenes. Since the hybrid photo-biocatalysts are insoluble, they can be readily recovered and recycled. This work opens new avenues to create artificial photo-biocatalyst systems, enabling the facile coupling of renewable solar energy and sustainable chemical production.