Photobiocatalysis: Activating Redox Enzymes by Direct or Indirect Transfer of Photoinduced Electrons

Abstract

Biocatalytic transformation has received increasing attention in the green synthesis of chemicals because of the diversity of enzymes, their high catalytic activities and specificities, and mild reaction conditions. The idea of solar energy utilization in chemical synthesis through the combination of photocatalysis and biocatalysis provides an opportunity to make the "green" process greener. Oxidoreductases catalyze redox transformation of substrates by exchanging electrons at the enzyme's active site, often with the aid of electron mediator(s) as a counterpart. Recent progress indicates that photoinduced electron transfer using organic (or inorganic) photosensitizers can activate a wide spectrum of redox enzymes to catalyze fuel-forming reactions (e.g., H evolution, CO reduction) and synthetically useful reductions (e.g., asymmetric reduction, oxygenation, hydroxylation, epoxidation, Baeyer-Villiger oxidation). This Review provides an overview of recent advances in light-driven activation of redox enzymes through direct or indirect transfer of photoinduced electrons.

Interfacing Formate Dehydrogenase with Metal Oxides for the Reversible Electrocatalysis and Solar‐Driven Reduction of Carbon Dioxide

“…In semi-artificial systems,rapid electron transfer from TiO 2 to the enzyme was previously found to be essential for efficient catalysis, [22,31] suggesting that the strong interfacial interaction plays an important role for the high activity and stability of dye j TiO 2 j FDH.P reviously reported photocatalyst systems employing NAD + -dependent FDHsf or CO 2 reduction to formate rely on soluble redox mediators and only produced TOFs in the range of 10-20 h À1 . [32] In summary, FDH immobilized on metal-oxide electrodes is established as ar eversible electrocatalyst for the selective conversion of CO 2 to formate.T he porous metal-oxide scaffolds allow for high FDH loading and consequently high current densities,w hich makes the protein-modified electrodes not only arelevant model system for CO 2 utilization, but also for formate oxidation in formate fuel cells.Anexcellent interface between TiO 2 and FDH is confirmed by QCM analysis and ATR-IR spectroscopy.T he direct (diffusional mediator-free) electron transfer across the enzyme-metaloxide interface is exploited for visible-light-driven CO 2 reduction to formate.T hese results underline the importance of characterizing the interactions at the enzyme-material interface and future improvements in performance may arise from more controlled immobilization and more efficient electron transfer with the directly wired FDH.…”

A Photoenzymatic NADH Regeneration System

“…In the 1970s, Willner and co‐workers pioneered the use of visible light as a driving force to promote in situ NADPH regeneration . Despite the promise of sunlight‐driven cofactor regeneration, it was only in a few follow‐up studies that this approach was further developed . One reason is that photochemical redox reactions comprise single‐electron‐transfer steps, which makes their direct application to NAD(P) + reduction impractical.…”

“…1.18.1.5) as a relay system. Striving for simple reaction setups, we evaluated flavins as photocatalysts . Overall, we aimed at establishing a photoenzymatic NADH regeneration system applicable to NADH‐dependent, stereospecific reduction reactions (Scheme ).…”

TiO2‐Based Photocatalysis at the Interface with Biology and Biomedicine

“…The most widely used photo‐biocatalysts make use of cb electrons of SCs, which are transferred to the redox center of enzymes. Photoactivation can be achieved through direct (Figure , path II) or indirect transfer, with a mediator (Figure , path I) …”