JBIC Journal of Biological Inorganic Chemistry

, Volume 9, Issue 3, pp 247–255

Chloride ligation in inorganic manganese model compounds relevant to Photosystem II studied using X-ray absorption spectroscopy

Authors

  • Shelly A. Pizarro
    • Melvin Calvin Laboratory, Physical Biosciences DivisionLawrence Berkeley National Laboratory
    • Department of ChemistryUniversity of California
    • Sandia National Labs
  • Hendrik Visser
    • Melvin Calvin Laboratory, Physical Biosciences DivisionLawrence Berkeley National Laboratory
    • Department of ChemistryUniversity of California
  • Roehl M. Cinco
    • Melvin Calvin Laboratory, Physical Biosciences DivisionLawrence Berkeley National Laboratory
    • Department of ChemistryUniversity of California
  • John H. Robblee
    • Melvin Calvin Laboratory, Physical Biosciences DivisionLawrence Berkeley National Laboratory
    • Department of ChemistryUniversity of California
    • Chemistry DepartmentMassachusetts Institute of Technology
  • Samudranil Pal
    • Department of Chemistry, Eugene F. Merkert Chemistry CenterBoston College
    • School of ChemistryUniversity of Hyderabad
  • Sumitra Mukhopadhyay
    • Department of Chemistry, Eugene F. Merkert Chemistry CenterBoston College
    • Chemistry DepartmentMassachusetts Institute of Technology
  • Henry J. Mok
    • Department of Chemistry, Eugene F. Merkert Chemistry CenterBoston College
    • CIS-US Inc.
  • Kenneth Sauer
    • Melvin Calvin Laboratory, Physical Biosciences DivisionLawrence Berkeley National Laboratory
    • Department of ChemistryUniversity of California
  • Karl Wieghardt
    • Max Planck Institut für Bioorganische Chemie
  • William H. Armstrong
    • Department of Chemistry, Eugene F. Merkert Chemistry CenterBoston College
    • Melvin Calvin Laboratory, Physical Biosciences DivisionLawrence Berkeley National Laboratory
Original Article

DOI: 10.1007/s00775-003-0520-1

Cite this article as:
Pizarro, S.A., Visser, H., Cinco, R.M. et al. J Biol Inorg Chem (2004) 9: 247. doi:10.1007/s00775-003-0520-1

Abstract

Chloride ions are essential for proper function of the photosynthetic oxygen-evolving complex (OEC) of Photosystem II (PS II). Although proposed to be directly ligated to the Mn cluster of the OEC, the specific structural and mechanistic roles of chloride remain unresolved. This study utilizes X-ray absorption spectroscopy (XAS) to characterize the Mn–Cl interaction in inorganic compounds that contain structural motifs similar to those proposed for the OEC. Three sets of model compounds are examined; they possess core structures MnIV3O4X (X=Cl, F, or OH) that contain a di-μ-oxo and two mono-μ-oxo bridges or MnIV2O2X (X=Cl, F, OH, OAc) that contain a di-μ-oxo bridge. Each set of compounds is examined for changes in the XAS spectra that are attributable to the replacement of a terminal OH or F ligand, or bridging OAc ligand, by a terminal Cl ligand. The X-ray absorption near edge structure (XANES) shows changes in the spectra on replacement of OH, OAc, or F by Cl ligands that are indicative of the overall charge of the metal atom and are consistent with the electronegativity of the ligand atom. Fourier transforms (FTs) of the extended X-ray absorption fine structure (EXAFS) spectra reveal a feature that is present only in compounds where chloride is directly ligated to Mn. These FT features were simulated using various calculated Mn–X interactions (X=O, N, Cl, F), and the best fits were found when a Mn–Cl interaction at a 2.2–2.3 Å bond distance was included. There are very few high-valent Mn halide complexes that have been synthesized, and it is important to make such a comparative study of the XANES and EXAFS spectra because they have the potential for providing information about the possible presence or absence of halide ligation to the Mn cluster in PS II.

Keywords

Chloride cofactorK-edge absorptionManganese EXAFSPhotosystem II

Abbreviations

bpea

N,N-bis(2-pyridylmethyl)ethylamine

EXAFS

extended X-ray absorption fine structure

FT

Fourier transform

IPE

inflection point energy

OEC

oxygen evolving complex

PS II

Photosystem II

tacn

1,4,7-triazacyclononane

XANES

X-ray absorption near edge structure

XAS

X-ray absorption spectroscopy

XRD

X-ray diffraction

Supplementary material

supp.pdf (59 kb)
Supplementary material (PDF 60 KB)

Copyright information

© SBIC 2004