Skip to main content

Lund University Publications

LUND UNIVERSITY LIBRARIES

Site-selective x-ray spectroscopy on an asymmetric model complex of the [FeFe] hydrogenase active site

Leidel, Nils ; Chernev, Petko ; Havelius, Kajsa G.V. LU ; Ezzaher, Salah ; Ott, Sascha and Haumann, Michael (2012) In Inorganic Chemistry 51(8). p.4546-4559
Abstract

The active site for hydrogen production in [FeFe] hydrogenase comprises a diiron unit. Bioinorganic chemistry has modeled important features of this center, aiming at mechanistic understanding and the development of novel catalysts. However, new assays are required for analyzing the effects of ligand variations at the metal ions. By high-resolution X-ray absorption spectroscopy with narrow-band X-ray emission detection (XAS/XES = XAES) and density functional theory (DFT), we studied an asymmetrically coordinated [FeFe] model complex, [(CO) 3Fe I1-(bdtCl 2)-Fe I2(CO)(Ph 2P-CH 2-NCH 3-CH 2-PPh 2)] (1, bdt = benzene-1,2-dithiolate), in... (More)

The active site for hydrogen production in [FeFe] hydrogenase comprises a diiron unit. Bioinorganic chemistry has modeled important features of this center, aiming at mechanistic understanding and the development of novel catalysts. However, new assays are required for analyzing the effects of ligand variations at the metal ions. By high-resolution X-ray absorption spectroscopy with narrow-band X-ray emission detection (XAS/XES = XAES) and density functional theory (DFT), we studied an asymmetrically coordinated [FeFe] model complex, [(CO) 3Fe I1-(bdtCl 2)-Fe I2(CO)(Ph 2P-CH 2-NCH 3-CH 2-PPh 2)] (1, bdt = benzene-1,2-dithiolate), in comparison to iron-carbonyl references. Kβ emission spectra (Kβ 1,3, Kβ′) revealed the absence of unpaired spins and the low-spin character for both Fe ions in 1. In a series of low-spin iron compounds, the Kβ 1,3 energy did not reflect the formal iron oxidation state, but it decreases with increasing ligand field strength due to shorter iron-ligand bonds, following the spectrochemical series. The intensity of the valence-to-core transitions (Kβ 2,5) decreases for increasing Fe-ligand bond length, certain emission peaks allow counting of Fe-CO bonds, and even molecular orbitals (MOs) located on the metal-bridging bdt group of 1 contribute to the spectra. As deduced from 3d → 1s emission and 1s → 3d absorption spectra and supported by DFT, the HOMO-LUMO gap of 1 is about 2.8 eV. Kβ-detected XANES spectra in agreement with DFT revealed considerable electronic asymmetry in 1; the energies and occupancies of Fe-d dominated MOs resemble a square-pyramidal Fe(0) for Fe1 and an octahedral Fe(II) for Fe2. EXAFS spectra for various Kβ emission energies showed considerable site-selectivity; approximate structural parameters similar to the crystal structure could be determined for the two individual iron atoms of 1 in powder samples. These results suggest that metal site- and spin-selective XAES on [FeFe] hydrogenase protein and active site models may provide a powerful tool to study intermediates under reaction conditions.

(Less)
Please use this url to cite or link to this publication:
author
; ; ; ; and
publishing date
type
Contribution to journal
publication status
published
in
Inorganic Chemistry
volume
51
issue
8
pages
14 pages
publisher
The American Chemical Society (ACS)
external identifiers
  • scopus:84859799331
  • pmid:22443530
ISSN
0020-1669
DOI
10.1021/ic2024154
language
English
LU publication?
no
id
94f19256-d6a4-4db0-a526-15d0c1bd11e7
date added to LUP
2020-01-15 10:18:29
date last changed
2024-08-07 13:20:24
@article{94f19256-d6a4-4db0-a526-15d0c1bd11e7,
  abstract     = {{<p>The active site for hydrogen production in [FeFe] hydrogenase comprises a diiron unit. Bioinorganic chemistry has modeled important features of this center, aiming at mechanistic understanding and the development of novel catalysts. However, new assays are required for analyzing the effects of ligand variations at the metal ions. By high-resolution X-ray absorption spectroscopy with narrow-band X-ray emission detection (XAS/XES = XAES) and density functional theory (DFT), we studied an asymmetrically coordinated [FeFe] model complex, [(CO) <sub>3</sub>Fe <sup>I</sup>1-(bdtCl <sub>2</sub>)-Fe <sup>I</sup>2(CO)(Ph <sub>2</sub>P-CH <sub>2</sub>-NCH <sub>3</sub>-CH <sub>2</sub>-PPh <sub>2</sub>)] (1, bdt = benzene-1,2-dithiolate), in comparison to iron-carbonyl references. Kβ emission spectra (Kβ <sup>1,3</sup>, Kβ′) revealed the absence of unpaired spins and the low-spin character for both Fe ions in 1. In a series of low-spin iron compounds, the Kβ <sup>1,3</sup> energy did not reflect the formal iron oxidation state, but it decreases with increasing ligand field strength due to shorter iron-ligand bonds, following the spectrochemical series. The intensity of the valence-to-core transitions (Kβ <sup>2,5</sup>) decreases for increasing Fe-ligand bond length, certain emission peaks allow counting of Fe-CO bonds, and even molecular orbitals (MOs) located on the metal-bridging bdt group of 1 contribute to the spectra. As deduced from 3d → 1s emission and 1s → 3d absorption spectra and supported by DFT, the HOMO-LUMO gap of 1 is about 2.8 eV. Kβ-detected XANES spectra in agreement with DFT revealed considerable electronic asymmetry in 1; the energies and occupancies of Fe-d dominated MOs resemble a square-pyramidal Fe(0) for Fe1 and an octahedral Fe(II) for Fe2. EXAFS spectra for various Kβ emission energies showed considerable site-selectivity; approximate structural parameters similar to the crystal structure could be determined for the two individual iron atoms of 1 in powder samples. These results suggest that metal site- and spin-selective XAES on [FeFe] hydrogenase protein and active site models may provide a powerful tool to study intermediates under reaction conditions.</p>}},
  author       = {{Leidel, Nils and Chernev, Petko and Havelius, Kajsa G.V. and Ezzaher, Salah and Ott, Sascha and Haumann, Michael}},
  issn         = {{0020-1669}},
  language     = {{eng}},
  month        = {{04}},
  number       = {{8}},
  pages        = {{4546--4559}},
  publisher    = {{The American Chemical Society (ACS)}},
  series       = {{Inorganic Chemistry}},
  title        = {{Site-selective x-ray spectroscopy on an asymmetric model complex of the [FeFe] hydrogenase active site}},
  url          = {{http://dx.doi.org/10.1021/ic2024154}},
  doi          = {{10.1021/ic2024154}},
  volume       = {{51}},
  year         = {{2012}},
}