Molecular Inhibition for Selective CO2 Conversion

Electrochemical CO2 reduction presents a sustainable route to the production of chemicals and fuels. Achieving a narrow product distribution with copper catalysts is challenging and conventional material modifications offer limited control over selectivity. Here, we show that the mild cathodic potentials required to reach high currents in an alkaline gas-fed flow cell permits retention of a surface-bound thiol (4-mercaptopyridine), enabling molecule-directed selective formate generation at high reaction rates. Combined experimental and computational results showed that formate production is favoured due to the inhibition of a CO producing pathway caused by destabilising interactions with the anchored molecule. The immobilisation of molecules to inhibit specific carbon-based products therefore offers a novel approach to rationally tune the selectivity of heterogeneous catalysts.

Bioconversion of Carbon Monoxide to Formate Using Artificially Designed Carbon Monoxide:Formate Oxidoreductase in Hyperthermophilic Archaea

Ferredoxin-dependent metabolic engineering of electron transfer circuits has been developed to enhance redox efficiency in the field of synthetic biology, e.g., for hydrogen production and for reduction of flavoproteins or NAD(P)+. Here, we present the bioconversion of carbon monoxide (CO) gas to formate via a synthetic CO:formate oxidoreductase (CFOR), designed as an enzyme complex for direct electron transfer between noninteracting CO dehydrogenase and formate dehydrogenase using an electron-transferring Fe-S fusion protein. The CFOR-introduced Thermococcus onnurineus mutant strains showed CO-dependent formate production in vivo and in vitro. The formate production rate from purified CFOR complex and specific formate productivity from the bioreactor were 348 ± 34 μmol/mg/min and 90.2 ± 20.4 mmol/g-cells/h, respectively. The CO-dependent CO2 reduction/formate production activity of synthetic CFOR was confirmed, indicating that direct electron transfer between two unrelated dehydrogenases was feasible via mediation of the FeS-FeS fusion protein.