Photobiocatalytic chemistry of oxidoreductases using water as the electron donor

Abstract

To date, water has been poorly studied as the sacrificial electron donor for biocatalytic redox reactions using isolated enzymes. Here we demonstrate that water can also be turned into a sacrificial electron donor to promote biocatalytic redox reactions. The thermodynamic driving force required for water oxidation is obtained from UV and visible light by means of simple titanium dioxide-based photocatalysts. The electrons liberated in this process are delivered to an oxidoreductase by simple flavin redox mediators. Overall, the feasibility of photobiocatalytic, water-driven bioredox reactions is demonstrated.

Photobiocatalysis: The Power of Combining Photocatalysis and Enzymes

“…In a pioneering work coupling photocatalysis with enzymes, Hollmann and Corma [67] have combined the photocatalytic activity of Au nanoparticles (NPs) supported on TiO 2 with the enzymatic activity of oxidoreductase by means of FAD + as mediator and cofactor to achieve the stereospecific hydrogenation of conjugated C=C bonds of ketoisophorone (See Scheme 12). In previous work in the literature, [34] Au/TiO 2 has been found to be a highly efficient photocatalyst for hydrogen generation from water-methanol mixtures under sunlight irradiation and exhibiting photocatalytic response even under exclusive visible light irradiation.…”

“…Electrons in the conduction band of TiO 2 or on Au NPs should reduce FAD + to the corresponding reduced form FADH 2 that is the cofactor necessary to activate the oxidoreductase. The oxidoreductase in this study was obtained from E. Coli BL21 (DE3) that was transfected with a gene encoding the wanted enzyme [67] . After activation of the oxidoreductase with FADH 2 , the enzyme exhibits activity to convert ketoisophorone to the corresponding (R)-levodione.…”

“…Kinetic studies have shown that the rate limiting step of the process is the photocatalytic regeneration of the flavin FADH 2 due to the difficulty in achieving water oxidation. [67] ).…”

Tandem Reactions Combining Biocatalysts and Chemical Catalysts for Asymmetric Synthesis

“…Additionally, similar to the incorporation of transition-metal complexes within supramolecular host-guest complexes, the use of artificial metalloenzymes enables the Instead of coupling with oxidation enzymes, photoredox catalysts, working as hydride transfer catalysts, have also been incorporated with reductases such as alcohol dehydrogenase [72] and glucose dehydrogenase [73] to prepare chiral alcohols and L-glutamate respectively. Unlike the aforementioned studies in which organic sacrificial electron donors were used, Corma and co-workers used light-driven and titanium dioxide-promoted water oxidation to drive redox reactions catalyzed by flavin-based old yellow enzyme (OYE) (Scheme 11) [74]. The protons and electrons were generated by Au/TiO 2 photoredox catalyst via the oxidation of water under UV irradiation, and then were supplied to the flavin of old yellow enzymes for asymmetrically reducing conjugated C=C bonds.…”

“…FMN, flavin mononucleotide, OYE, old yellow enzyme. Reprinted with permission from Macmillan Publishers Ltd.: Nature Chemistry [74]. Copyright 2014.…”