Nickel(I) in an All-Ferric NiFeS Cluster

Area of Science:

• Bioinorganic Chemistry
• Biochemistry
• Enzyme Mechanisms

Background:

• Anaerobic carbon monoxide dehydrogenase (CODH) enzymes are crucial for interconverting CO2 and CO.
• The active site, the C-cluster ([NiFe3S4]-Feu), has an unresolved electronic structure and ambiguous metal oxidation states.
• Understanding the C-cluster's electronic properties is key to elucidating CODH function.

Purpose of the Study:

• To model the CODH C-cluster using synthetic [NiFe3S4] cores in various oxidation states.
• To resolve the electronic structure and metal oxidation states within the C-cluster.
• To investigate the accessibility of different nickel oxidation states.

Main Methods:

• Synthesis of [NiFe3S4]3+/2+/1+ clusters.
• Characterization via X-ray crystallography, spectroscopy (including XAS), and magnetism.
• Computational analysis to support experimental findings.

Main Results:

• The most oxidized cluster ([NiFe3S4]3+) features Ni2+ and Fe3+ sites.
• Reduction to the [NiFe3S4]2+ state surprisingly leads to Ni1+ reduction, not Fe3+.
• The Fe3+ subsite reduction is dependent on nickel reaching the Ni1+ state.

Conclusions:

• Nickel (Ni) can readily adopt the Ni1+ oxidation state in FeS clusters relevant to CODH.
• The electronic structure and oxidation states of the CODH C-cluster are better understood through these synthetic models.
• This work provides insights into the mechanism of CO2/CO interconversion by CODH enzymes.