title: Simulation of the isotropic EXAFS spectra for the S2 and S3 structures of the oxygen evolving complex in photosystem II.
abstract: Most of the main features of water oxidation in photosystem II are now well understood, including the mechanism for O-O bond formation. For the intermediate S2 and S3 structures there is also nearly complete agreement between quantum chemical modeling and experiments. Given the present high degree of consensus for these structures, it is of high interest to go back to previous suggestions concerning what happens in the S2-S3 transition. Analyses of extended X-ray adsorption fine structure (EXAFS) experiments have indicated relatively large structural changes in this transition, with changes of distances sometimes larger than 0.3 Å and a change of topology. In contrast, our previous density functional theory (DFT)(B3LYP) calculations on a cluster model showed very small changes, less than 0.1 Å. It is here found that the DFT structures are also consistent with the EXAFS spectra for the S2 and S3 states within normal errors of DFT. The analysis suggests that there are severe problems in interpreting EXAFS spectra for these complicated systems.
authors.affiliation: College of Chemistry, Beijing Normal University, 100875 Beijing, China;
authors.forename: Xichen
authors.initials: X
authors.lastname: Li
authors.affiliation: Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden; and ps@physto.se.
authors.forename: Per E M
authors.initials: PE
authors.lastname: Siegbahn
authors.affiliation: Department of Theoretical Chemistry, Chemical Center, Lund University, S-22100 Lund, Sweden.
authors.forename: Ulf
authors.initials: U
authors.lastname: Ryde
mesh_terms: D000465:Algorithms; D000596:Amino Acids / Q000737:chemistry; D003198:Computer Simulation; D006878:Hydroxides / Q000737:chemistry; D008024:Ligands; D008345:Manganese / Q000737:chemistry; D008958:Models, Molecular; D010100:Oxygen / Q000737:chemistry; D010788:Photosynthesis; D045332:Photosystem II Protein Complex / Q000737:chemistry*; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D015203:Reproducibility of Results; D012984:Software; D013053:Spectrophotometry
chemical_list: D000596:Amino Acids; D006878:Hydroxides; D008024:Ligands; D045332:Photosystem II Protein Complex; D008345:Manganese; D010100:Oxygen
keywords: EXAFS refinement; S-state structures; density functional theory; water oxidation