Effective Artificial Co-enzyme Based on Single-Electron Reduced Form of 2,2′-Bipyridinium Salt Derivatives for Formate Dehydrogenase in the Catalytic Conversion of CO2 to Formic Acid

Abstract

Formate dehydrogenase (FDH) is a useful biocatalyst for CO2 reduction to formic acid in a photoredox system consisting of a photosensitizer and an electron carrier. The electron carrier, single-electron reduced 2,2′-bipyridinium salts (2,2′-BP2+s) act as the co-enzyme for FDH in the reaction of CO2 to formic acid. An advantage of 2,2′-BP2+s is the easy change of structural geometry and the various single-electron reduction potentials. For further improvement of CO2 reduction catalytic activity of FDH, various 2,2′-BP2+s were synthesized as effective artificial co-enzymes for FDH. The effect of the structural geometry and the single-electron reduction potential in the single-electron reduced form of 2,2′-BP2+s on the CO2 reduction catalytic activity of FDH was studied by enzymatic kinetic analysis in detail for the first time. Especially, the catalytic efficiency, kcat/Km value of the single-electron reduced 1,1′-ethylene-2,2′-bipyridinium salt was c.a. 126 times larger than that of native co-enzyme, NADH. These results showed that catalytic activity of FDH can be manipulated with complete control by using 2,2′-BP2+ without changing the structure of FDH and has opened a new avenue for the approach of NAD+/NADH redox free system with FDH using an inexpensive small electron carrier molecule.

Strategies for Bioelectrochemical CO2 Reduction

“…Rather than using the native coenzyme, Amao and colleagues used the artificial small molecule 2,2′‐bipyridinium (BP) as an alternative electron carrier. The reduced 1,1′‐ethylene‐2,2′‐BP salt demonstrated 126‐fold catalytic efficiency compared to NADH . A carbamoyl‐substituted BP (CMV) demonstrated enhanced binding affinity with FDH and improved catalytic activity for CO 2 reduction compared to BP …”

“…[18] Rather than using the native coenzyme, Amao and colleagues used the artificial smallmolecule 2,2'-bipyridinium (BP) as an alternative electron carrier.T he reduced 1,1'-ethylene-2,2'-BP salt demonstrated 126-fold catalytic efficiency compared to NADH. [19] Ac arbamoyl-substituted BP (CMV) demonstrated enhanced binding affinity with FDH and improvedcatalytic activity for CO 2 reduction compared to BP. [20] In general, NADH-dependentF DHs have low catalytic rate constants (k cat )f or CO 2 reduction due to the energetically unfavorable electron transfer process from NAD + /NADH (À0.32 V vs. SHE) to CO 2 /HCOO À (À0.42 Vv s. SHE).…”

Visible‐Light Driven CO2 Reduction to Formate with Electron Mediated Nicotinamide‐Modified Viologen in the System of Water‐Soluble Zinc Porphyrin and Formate Dehydrogenase

“…In this system, the single‐electron reduced BPs act as a co‐enzyme for CbFDH instead of NADH. We previously reported the kinetic parameters of the single‐electron reduced various 4,4’‐ [27–30] and 2,2’‐BPs [31,32] for the CO 2 reduction to formate with CbFDH by using an enzymatic kinetic analysis. In order to elucidate the electron supply process using single‐electron reduced 4,4’‐BP as a co‐enzyme in the reduction process of CO 2 to formate catalyzed by CbFDH, moreover, the mechanism was clarified by experimental (enzyme reaction kinetics, electrochemical method) and quantum chemical analyses (docking simulation and density functional theory (DFT) calculation) [33] …”

Photoelectrochemical CO2 Reduction to Formate with the Sacrificial Reagent Free System of Semiconductor Photocatalysts and Formate Dehydrogenase

“…In this system, the single‐electron reduced BPs acts as a co‐enzyme for FDH instead of NADH. Recently, we reported the kinetic parameters of the single‐electron reduced 4,4’‐ and 2,2’‐BPs for the CO 2 reduction to formate with FDH using an enzymatic kinetic analysis. From an enzymatic kinetic analysis, formate production from CO 2 only proceeds with FDH using single‐electron reduced 4,4’‐ and 2,2’‐BPs.…”