Peroxygenases offer an attractive means to address challenges in selective oxyfunctionalization chemistry. Despite this, their application in synthetic chemistry remains challenging due to their facile inactivation by the stoichiometric oxidant H₂O₂. Often atom-inefficient peroxide generation systems are required, which show little potential for large-scale implementation. Here, we show that visible-light-driven, catalytic water oxidation can be used for in situ generation of H₂O₂ from water, rendering the peroxygenase catalytically active. In this way, the stereoselective oxyfunctionalization of hydrocarbons can be achieved by simply using the catalytic system, water and visible light.

Alcohol dehydrogenases are well-established catalysts for various reduction reactions. However, the reduction of carboxylic acid derivatives has not yet been reported with these enzymes. In this contribution, we demonstrated that carboxylic acid thioesters could be readily reduced by a range of alcohol dehydrogenases, albeit at significantly reduced rates relative to those observed for corresponding ketones. A molecular explanation, especially for the lower turnover rates for thioesters relative to those obtained for ketones, is presented, as is a preliminary substrate scope.

Peroxygenases are very promising catalysts for oxyfunctionalization reactions. Their practical applicability, however, is hampered by their sensitivity against the oxidant (H₂O₂), therefore necessitating in situ generation of H₂O₂. Here, we report a photoelectrochemical approach to provide peroxygenases with suitable amounts of H₂O₂ while reducing the electrochemical overpotential needed for the reduction of molecular oxygen to H₂O₂. When tethered on single-walled carbon nanotubes (SWNTs) under illumination, flavins allowed for a marked anodic shift of the oxygen reduction potential in comparison to pristine SWNT and/or nonilluminated electrodes. This flavin-SWNT-based photoelectrochemical platform enabled peroxygenases-catalyzed, selective hydroxylation reactions.

The peroxygenase from Agrocybe aegerita (AaeUPO) has been evaluated for stereoselective oxyfunctionalization chemistry under non-aqueous reaction conditions. The stereoselective hydroxylation of ethylbenzene to (R)-1-phenylethanol was performed in neat substrate as reaction medium together with the immobilized biocatalyst and ^tertBuOOH as oxidant. Stability and activity issues still have to be addressed. Nevertheless, gram-scale production of enantiopure (R)-1-phenylethanol was achieved with respectable 90,000 turnovers of the biocatalyst.

Photosynthesis may be described as light-driven oxidation of water and subsequent use of the generated reducing equivalents to fix CO₂ and synthesize higher energy organic compounds, such as carbohydrates. The transposition of the sustainable and atom-efficient strategy of water oxidation to in vitro controlled biocatalytic reactions is poorly studied but is of high interest for the development of photobiocatalysis, and eco-friendly catalytic tools in a wider sense. Here we demonstrate that light-driven oxidation of water catalysed by vanadium-doped TiO₂ (V-TiO₂), a re-usable photocatalyst, can provide the electrons that lytic polysaccharide monooxygenases (LPMOs) need to oxidatively deconstruct biomass polysaccharides. The demonstration that electrons may be generated by water oxidation alleviates the need for an externally added electron donor, which so far has been a prerequisite for LPMO activity. Importantly, photocatalytic LPMO activation was achieved in the absence of redox mediators, which represents the first demonstration of mediator-free electron transfer from V-TiO₂ particles to a redox enzyme, expanding the repertoire of known and conceivable photobiocatalytic reactions. Fundamentally, this photobiocatalytic system allows activation and tight control of LPMO activity, thus offering new tools for mechanistic studies of these industrially important and ubiquitous enzymes. The latter is illustrated by real-time studies of the redox state of an LPMO, using the controllable light-V-TiO₂ technology for LPMO reduction and a novel fluorescence method for monitoring re-oxidation. We also show that the light-V-TiO₂ technology may be used to study pre-activation of LPMOs.

Oxidoreductases are promising catalysts for organic synthesis. To sustain their catalytic cycles they require efficient supply with redox equivalents. Today classical biomimetic approaches utilizing natural electron supply chains prevail but artificial regeneration approaches bear the promise of simpler and more robust reaction schemes. Utilizing visible light can accelerate such artificial electron transport chains and even enable thermodynamically unfeasible reactions such as the use of water as reductant. This contribution critically summarizes the current state of the art in photoredoxbiocatalysis (i.e. light-driven biocatalytic oxidation and reduction reactions).