Direct detection of a single[4Fe-4S]cluster in a tungsten-containing enzyme:Electrochemical conversion of CO_(2) into formate by formate dehydrogenase

The conversion of CO_(2) into fuels and valuable chemicals is one of the central topics to combat climate change and meet the growing demand for renewable energy.Herein,we show that the formate dehydrogenase from Clostridium ljungdahlii(ClFDH)adsorbed on electrodes displays clear characteristic voltammetric signals that can be assigned to the reduction and oxidation potential of the[4Fe-4S]^(2+/+)cluster under nonturnover conditions.Upon adding substrates,the signals transform into a specific redox center that engages in catalytic electron transport.ClFDH catalyzes rapid and efficient reversible interconversion between CO_(2) and formate in the presence of substrates.The turnover frequency of electrochemical CO_(2) reduction is determined as 1210 s^(-1) at 25℃ and pH 7.0,which can be further enhanced up to 1786 s^(-1) at 50℃.The Faradaic efficiency at−0.6 V(vs.standard hydrogen electrode)is recorded as 99.3%in a 2-h reaction.Inhibition experiments and theoretical modeling disclose interesting pathways for CO_(2) entry,formate exit,and OCN−competition,suggesting an oxidation-state-dependent binding mechanism of catalysis.Our results provide a different perspective for understanding the catalytic mechanism of FDH and original insights into the design of synthetic catalysts.

Surface modification of HKUST-1 for enhanced activity of immobilized formate dehydrogenase used in CO_(2)hydrogenation

Post synthetic modification of a hydrophilic metal-organic framework(MOF),HKUST-1,with stearic acid(SA)was carried out to enhance the stability of HKUST-1 in aqueous solution to be used as a support for formate dehydrogenase(FDH)used for CO_(2)conversion to formate.SA modification improved the hydrophobicity without affecting the morphology and crystal structure of MOF.Adsorption of FDH on the modified MOF(SA@HKUST-1)was compared to that of the native HKUST-1 and ZIF-L.The adsorption kinetics on all MOFs was found to follow pseudo-second order kinetics and the isotherm was best described by Freundlich model.The high stability of SA@HKUST-1 and enhanced hydrophobic interaction between support and CO_(2)resulted in high catalytic efficiency and stability of FDH@SA@HKUST-1.The immobilized enzyme retained 95.1%of its initial activity after 4 cycles of repeated use.It was also shown that FDH@SA@HKUST-1 retained morphology and crystal structure after repeated use.Results of the present work provide novel insight into the influence of hydrophobic MOFs on the activity and stability of immobilized FDH.These findings are expected to assist in developing highly active and stable biocatalysts for CO_(2)hydrogenation at commercial level.