Abstract
Efficient and cost effective nicotinamide cofactor regeneration is essential for industrial-scale bio-hydrogenations employing flavin-containing biocatalysts such as the Old Yellow Enzymes. A direct flavin regeneration system using visible light to initiate a photoredox cycle and drive biocatalysis is described, and shown to be effective in driving biocatalytic activated alkene reduction. Using Ru(ii) or Ir(iii) complexes as photosensitizers, coupled with an electron transfer mediator (methyl viologen) and sacrificial electron donor (triethanolamine) drives catalytic turnover of two Old Yellow Enzymes with multiple oxidative substrates. Therefore, there is great potential in the development of light-driven biocatalytic systems, providing an alternative to the reliance on enzyme-based cofactor regeneration systems.
Highlights
A variety of photosensitizers encompassing organic compounds,[15,16,17,18,19,20,21] quantum dots[22] and coordination complexes[14,23,24,25,26,27,28] has been investigated in conjunction with enzymatic systems, for both mechanistic studies of electron transfer and studies of biocatalytic turnover
This paper describes the use of complexes of RuIJII) and IrIJIII) as photosensitizers for the generation of reducing equivalents in the catalytic turnover of the OYEs pentaerythritol tetranitrate reductase (PETNR)[36] from Enterobacter cloacae PB2 and the thermophilic Old Yellow Enzyme (TOYE) from Thermoanaerobacter pseudethanolicus E39.37 We describe the development of a coenzyme independent, diffusion controlled multi-component system, detail the influence of individual reaction parameters upon overall efficiency, and examine the applicability of the technique towards a number of common substrates
Details of the chromatography columns and running conditions are described in the Electronic supplementary information (ESI)†. 1H NMR spectra were recorded on a Bruker UltraShield or AV-400 spectrometer
Summary
A variety of photosensitizers encompassing organic compounds,[15,16,17,18,19,20,21] quantum dots[22] and coordination complexes[14,23,24,25,26,27,28] has been investigated in conjunction with enzymatic systems, for both mechanistic studies of electron transfer and studies of biocatalytic turnover. The most widely investigated photosensitizers are compounds of rutheniumIJII), those based upon the cation trisIJ2,2′bipyridyl)rutheniumIJII), [RuIJbpy)3]2+, and analogous polypyridyl complexes. A range of electrochemical techniques has been developed using direct, indirect or enzyme-coupled methodologies.[30,31,32] Such methods often suffer from low efficiencies due to unwanted side-reactions, and require the use of specialized equipment with limited scale-up potential. This paper describes the use of complexes of RuIJII) and IrIJIII) as photosensitizers for the generation of reducing equivalents in the catalytic turnover of the OYEs pentaerythritol tetranitrate reductase (PETNR)[36] from Enterobacter cloacae PB2 and the thermophilic Old Yellow Enzyme (TOYE) from Thermoanaerobacter pseudethanolicus E39.37 We describe the development of a coenzyme independent, diffusion controlled multi-component system, detail the influence of individual reaction parameters upon overall efficiency, and examine the applicability of the technique towards a number of common substrates
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