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The Fully Oxidized State of the Glutamate Coordinated O 2 -Tolerant [NiFe]-Hydrogenase Shows a Ni(III)/Fe(III) Open-Shell Singlet Ground State.

Ravi KumarMatthias Stein
Published in: Journal of the American Chemical Society (2023)
The oxygen tolerance of the [NiFe]-hydrogenase from H. thermoluteolus was recently assigned to originate from an unusual coordination sphere of the active site nickel atom (Shomura et al. Science 2017 , 357 , 928-932, 10.1126/science.aan4497). In the oxidized state, a terminal cysteine residue is displaced by a bidentate coordinating nearby Glu32 and thus moves to occupy a third μ-cysteine bridging position. Spectral features of the oxidized state were assigned to originate from a closed-shell Ni(IV)/Fe(II) state (Kulka-Peschke et al. J. Am. Chem. Soc. 2022 , 144 , 17022-17032, 10.1021/jacs.2c06400). Such a high-valent nickel oxidation state is unprecedented in biological systems. The spectral properties and the coordination sphere of that [NiFe]-hydrogenase can, however, also be rationalized by an energetically lower broken-symmetry Ni(III)/Fe(III) state of the active site which was not considered. In this open-shell singlet, the ligand-mediated antiferromagnetic spin-coupling leads to an overall S = 0 spin state with evenly distributed spin densities over the metal atoms. Experiments are suggested that may clarify the final assignment of redox states.
Keyphrases
  • room temperature
  • metal organic framework
  • magnetic resonance imaging
  • public health
  • single molecule
  • living cells