Light-driven carbon−carbon bond formation via CO₂reduction catalyzed by complexes of CdS nanorods and a 2-oxoacid oxidoreductase

Abstract

Redox enzymes are capable of catalyzing a vast array of useful reactions, but they require redox partners that donate or accept electrons. Semiconductor nanocrystals provide a mechanism to convert absorbed photon energy into redox equivalents for enzyme catalysis. Here, we describe a system for photochemical carbon−carbon bond formation to make 2-oxoglutarate by coupling CO2with a succinyl group. Photoexcited electrons from cadmium sulfide nanorods (CdS NRs) transfer to 2-oxoglutarate:ferredoxin oxidoreductase fromMagnetococcus marinusMC-1 (MmOGOR), which catalyzes a carbon−carbon bond formation reaction. We thereby decouple MmOGOR from its native role in the reductive tricarboxylic acid cycle and drive it directly with light. We examine the dependence of 2-oxoglutarate formation on a variety of factors and, using ultrafast transient absorption spectroscopy, elucidate the critical role of electron transfer (ET) from CdS NRs to MmOGOR. We find that the efficiency of this ET depends strongly on whether the succinyl CoA (SCoA) cosubstrate is bound at the MmOGOR active site. We hypothesize that the conformational changes due to SCoA binding impact the CdS NR−MmOGOR interaction in a manner that decreases ET efficiency compared to the enzyme with no cosubstrate bound. Our work reveals structural considerations for the nano−bio interfaces involved in light-driven enzyme catalysis and points to the competing factors of enzyme catalysis and ET efficiency that may arise when complex enzyme reactions are driven by artificial light absorbers.

Defining Intermediates of Nitrogenase MoFe Protein during N2 Reduction under Photochemical Electron Delivery from CdS Quantum Dots

“…The photoinduced electron injection from CdS QDs into MoFe protein relies on the binding interaction of the two species in solution. This interaction was characterized using dynamic light scattering (DLS) . MoFe protein from Azotobacter vinelandii ( Av ) was mixed with 4 nm diameter CdS QDs in a 1:1 molar ratio, which is the optimal ratio for photochemical reduction of N 2 .…”

Semi-biological approaches to solar-to-chemical conversion

“…204,205 Photochemical C-C bond formation has recently been realised in a CdS-2-oxoglutarate:ferredoxin oxidoreductase (OGOR) hybrid system. 206 The OGOR catalyses the amalgamation of CO 2 and succinate into 2-oxoglutarate and is part of the reductive tricarboxylic acid cycle responsible for CO 2 fixation in many autotrophic microorganisms. The irradiated CdS generates reducing equivalents to drive the catalytic turnover at OGOR which involves large substrates, significant conformational changes during catalysis, and eventual formation of C-C bonds.…”

“…The irradiated CdS generates reducing equivalents to drive the catalytic turnover at OGOR which involves large substrates, significant conformational changes during catalysis, and eventual formation of C-C bonds. 206 Functionalisation of C-H bonds provides a straightforward and atom-economical access towards a plethora of organic products, 207 where enzymes such as cyt P450 show their synthetic advantages. The hallmark reaction of cyt P450 is the hydroxylation of C-H bonds, during which the delivery of electrons from the NADH reductase is synchronised with the activation of oxygen at the haem centre.…”

Green Catalysts: Applied and Synthetic Photosynthesis

“…The upstream photochemical steps leading to CO2 fixation involved light absorption by (tris-bipyridine)ruthenium(II) to drive the formation of NADPH in the presence of a sacrificial donor and ferrodoxin-NADP + reductase. Recent work with nanoparticulate semiconductor photocatalysts have demonstrated similar enzyme mediated C-C bond formation with CO2 as a substrate [167].…”