4.7 Article

Activation Barriers of Oxygen Transformation at the Active Site of [FeFe] Hydrogenases

Journal

INORGANIC CHEMISTRY
Volume 53, Issue 22, Pages 11890-11902

Publisher

AMER CHEMICAL SOC
DOI: 10.1021/ic501049z

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Funding

  1. Schweizerischer Nationalfonds [200021L_138536]
  2. ETH Zurich [ETH-08 11-2]
  3. Swiss National Science Foundation (SNF) [200021L_138536] Funding Source: Swiss National Science Foundation (SNF)

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Oxygen activation at the active sites of [FeFe] hydrogenases has been proposed to be the initial step of irreversible oxygen-induced inhibition of these enzymes. On the basis of a first theoretical study into the thermodynamics of O-2 activation [Inorg. Chem. 2009, 48, 7127] we here investigate the kinetics of possible reaction paths at the distal iron atom of the active site by means of density functional theory. A sequence of steps is proposed to either form a reactive oxygen species (ROS) or fully reduce O-2 to water. In this reaction cascade, two branching points are identified where water formation directly competes with harmful oxygen activation reactions. The latter are water formation by O-O bond cleavage of a hydrogen peroxide-bound intermediate competing with H2O2 dissociation and CO2 formation by a putative iron-oxo species competing with protonation of the iron-oxo species to form a hydroxyo ligand. Furthermore, we show that proton transfer to activated oxygen is fast and that proton supply to the active site is vital to prevent ROS dissociation. If sufficiently many reduction equivalents are available, oxygen activation reactions are accelerated, and oxygen reduction to water becomes possible.

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