An internal electron reservoir enhances catalytic CO₂ reduction by a semisynthetic enzyme

Abstract

The development of an artificial metalloenzyme for CO2 reduction is described. The small-molecule catalyst [NiII (cyclam)]2+ has been incorporated within azurin. Selectivity for CO generation over H+ reduction is enhanced within the protein environment, while the azurin active site metal impacts the electrochemical overpotential and photocatalytic activity. The enhanced catalysis observed for copper azurin suggests an important role for intramolecular electron transfer, analogous to native CO2 reducing enzymes.

Transition metal-based catalysts for the electrochemical CO2reduction: from atoms and molecules to nanostructured materials

“…As an example, the axial coordination of the Ni-cyclam catalyst at a pendant histidine residue of azurin led to an artificial metalloenzyme active for CO 2 RR, displaying a positive shift in the onset catalytic potential under CO 2 compared to free [Ni(cyclam)] 2+ . 236 Although bulk electrolysis data were not reported, photocatalytic quantitative data showed an increased selectivity to CO for the azurin-[Ni(cyclam)] 2+ scaffold in comparison with free [Ni(cyclam)] 2+ , suggesting a critical role played by the protein environment. Moreover, the presence of the redox-active Cu center also had a remarkable impact on improving the selectivity towards CO 2 RR, mimicking the role of iron-sulfur clusters in CODH.…”

“…Owing to the extremely conformation-sensitive CO 2 RR process mediated by [Ni(cyclam)] 2+ , it was also speculated that the protein environment may induce constraints to geometrical distortions of the cyclam ligand, favoring CO 2 RR over HER. 236 Finally, Machan and co-workers demonstrated the possible implementation of homogeneous systems for CO 2 RR using a flow-cell technology. 237 More specifically, [Ni(cyclam)] 2+ was employed as a benchmark homogeneous electrocatalyst in a non-aqueous electrolyzer for CO 2 RR to CO based on a continuous flow-cell configuration (Fig.…”

Light‐driven catalysis with engineered enzymes and biomimetic systems

“…To guide activity and selectivity, Ni(II)-cyclam was introduced to a protein scaffold to yield an artificial CODH enzyme [215][216][217]. Azurin, a robust electron-transfer blue copper protein with a surface histidine residue (His83) available to bind Ni(II)-cyclam, was used for this work.…”

“…Azurin, a robust electron-transfer blue copper protein with a surface histidine residue (His83) available to bind Ni(II)-cyclam, was used for this work. An azurin mutant, H83Q/Q107H, was prepared to facilitate coordination of the catalyst with greater solvent exposure [215]. Azurin with either Cu or Zn in its native Cu-bonding site were used as scaffolds for Ni(II)-cyclam.…”

Strategies for Bioelectrochemical CO2 Reduction

“…Here, the important factor to increase selectivityo fC Op roduction over the more thermodynamically favored H 2 production is the protein microenvironment;t he active site metal (Cu) in azurin enhances catalysis by intramoleculare lectron transfer,m imicking the functionofn ative iron sulfur clusters in Ni-CODH. [32] CO 2 reduction to methanol CO 2 reduction to methanol requires six electrons and is considered av ery difficult process. It has been reportedt hat the combination of the three NADH-dependent enzymes, formate dehydrogenase (FDH), formaldehyde dehydrogenase (FLDH), and alcohol dehydrogenase (ADH) enables the production of methanol from CO 2 in am etabolically reversedr eactionc ascade.…”