10 research outputs found
Correction: Hydrogen-activation mechanism of [Fe] hydrogenase revealed by multi-scale modeling
ISSN:2041-6520ISSN:2041-653
Electric-Field Effects on the [FeFe]-Hydrogenase Active Site
The effect of a homogeneous electric field—as exerted by the protein environment and by an electrode potential—on the reactivity of the active site of [FeFe] hydrogenases is unravelled by density functional theory calculations.ISSN:1359-7345ISSN:1364-548
Theoretical <sup>57</sup>Fe Mössbauer Spectroscopy for Structure Elucidation of [Fe] Hydrogenase Active Site Intermediates
[Fe] hydrogenase is a hydrogen activating
enzyme that features a monoiron active site, which can be well characterized
by Mössbauer spectroscopy. Mössbauer spectra have been
measured of the CO and CN<sup>–</sup> inhibited species as
well as under turnover conditions [Shima, S. et al., J.
Am. Chem. Soc., 2005, 127, 10430]. This study presents calculated Mössbauer
parameters for various active-site models of [Fe] hydrogenase to provide
structural information about the species observed in experiment. Because
theoretical Mössbauer spectroscopy requires the parametrization
of observables from <i>first-principles</i> calculations
(i.e., electric-field gradients and contact densities) to the experimental
observables (i.e., quadrupole splittings and isomer shifts), nonrelativistic
and relativistic density functional theory methods are parametrized
against a reference set of Fe complexes specifically selected for
the application to the Fe center in [Fe] hydrogenase. With this methodology,
the measured parameters for the CO and CN<sup>–</sup> inhibited
complexes can be reproduced. Evidence for the protonation states of
the hydroxyl group in close proximity to the active site and for the
thiolate ligand, which could participate in proton transfer, is obtained.
The unknown resting state measured in the presence of the substrate
and under pure H<sub>2</sub> atmosphere is identified to be a water-coordinated
complex. Consistent with previous assignments based on infrared and
X-ray absorption near-edge spectroscopy, all measured Mössbauer
data can be reproduced with the active site’s iron atom being
in oxidation state +2
Activation Barriers of Oxygen Transformation at the Active Site of [FeFe] Hydrogenases
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<sub>2</sub> activation [<i>Inorg.
Chem.</i> <b>2009</b>, 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<sub>2</sub> 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 H<sub>2</sub>O<sub>2</sub> dissociation and CO<sub>2</sub> 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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