title: Two-dimensional (14)N HYSCORE spectroscopy of the coordination geometry of ligands in dimanganese di-μ-oxo mimics of the oxygen evolving complex of photosystem II.
abstract: We use two-dimensional hyperfine sublevel correlation (HYSCORE) spectroscopy to investigate the coordination geometry of the nitrogen ligands of biomimetic models of the oxygen-evolving complex of photosystem II. In the 2D HYSCORE spectroscopy study, [(bpy)2Mn(III)(μ-O)2Mn(IV)(bpy)2](ClO4)3 (bpy, 2,2'-bipyridine) (1) and [H2O(terpy)Mn(III)(μ-O)2Mn(IV)(terpy)OH2](NO3)3 (terpy = 2,2':6',2″-terpyridine) (2) exhibit electron-nuclear hyperfine interactions that depend on both the oxidation state of the manganese ion and the geometry of the nitrogen ligand. We observe four types of (14)N hyperfine interactions corresponding to the Mn(iii) and Mn(iv) ion of each mixed-valence complex and the equatorial and axial geometry of the ligand, respectively. The strongest and the weakest hyperfine interactions arise from the axial and equatorial ligands of the Mn(iii) ion, respectively. The hyperfine interactions of intermediate strength are due to the axial and equatorial ligands of the Mn(iv) ion. Based on the results of this study, we assign the location and ligand geometry of the Mn(iii) ion of the tetranuclear manganese-calcium-oxo cluster in the S2 state of photosystem II.
authors.affiliation: Department of Chemistry and Chemical Biology and The Baruch '60 Center for Biochemical Solar Energy Research, Rensselaer Polytechnic Institute, Troy, NY 12180, USA. lakshk@rpi.edu.
authors.forename: Ruchira
authors.initials: R
authors.lastname: Chatterjee
authors.forename: Sergey
authors.initials: S
authors.lastname: Milikisiyants
authors.forename: K V
authors.initials: KV
authors.lastname: Lakshmi
mesh_terms: D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy; D008024:Ligands; D017895:Manganese Compounds / Q000737:chemistry*; D018716:Molecular Mimicry; D010100:Oxygen / Q000737:chemistry*; D045332:Photosystem II Protein Complex / Q000737:chemistry*; D013057:Spectrum Analysis / Q000379:methods*
chemical_list: D008024:Ligands; D017895:Manganese Compounds; D045332:Photosystem II Protein Complex; D010100:Oxygen