Chloride ligation in inorganic manganese model compounds relevantto photosystem II studied using X-ray absorption spectroscopy

Journal Article · Tue Sep 23 04:00:00 EDT 2003 · Journal of Biological Inorganic Chemistry

OSTI ID:886819

Pizarro, Shelly A; Visser, Hendrik; Cinco, Roehl M; Robblee, John H; Pal, Samudranil; Mukhopadhyay, Sumitra; Mok, Henry J; Sauer, Kenneth; Wieghardt, Karl; Armstrong, William H; Yachandra, Vittal K

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-mu-oxo and two mono-mu-oxo bridges or MnIV2O2X (X = Cl, F, OH, OAc) that contain a di-mu-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 (FT) of the 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 to 2.3 angstrom 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 PSII.

• Research Organization: Ernest Orlando Lawrence Berkeley NationalLaboratory, Berkeley, CA (US)
• Sponsoring Organization: USDOE Director, Office of Science. Office of Basic EnergySciences. Chemical Sciences, Geosciences, and Biosciences Division; National Institutes of Health
• DOE Contract Number: AC02-05CH11231
• OSTI ID: 886819
• Report Number(s): LBNL--54912; BnR: KC0304000
• Journal Information: Journal of Biological Inorganic Chemistry, Journal Name: Journal of Biological Inorganic Chemistry Vol. 9
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
59 BASIC BIOLOGICAL SCIENCES
ABSORPTION
ABSORPTION SPECTROSCOPY
ATOMS
CHLORIDES
ELECTRONEGATIVITY
HALIDES
INORGANIC COMPOUNDS
MANGANESE
Photosystem II EXAFS
SPECTRA