Characterization of Oxygen Bridged Manganese Model Complexes Using Multifrequency 17O-Hyperfine EPR Spectroscopies and Density Functional Theory

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• 作者：Leonid Rapatskiy ; William M. Ames ; Montserrat P茅rez-Navarro ; Anton Savitsky ; Julia J. Griese ; Thomas Weyherm眉ller ; Hannah S. Shafaat ; Martin H枚gbom ; Frank Neese ; Dimitrios A. Pantazis ; Nicholas Cox
• 刊名：Journal of Physical Chemistry B
• 出版年：2015
• 出版时间：October 29, 2015
• 年：2015
• 卷：119
• 期：43
• 页码：13904-13921
• 全文大小：903K
• ISSN：1520-5207

文摘

Multifrequency pulsed EPR data are reported for a series of oxygen bridged (渭-oxo/渭-hydroxo) bimetallic manganese complexes where the oxygen is labeled with the magnetically active isotope ¹⁷O (I = 5/2). Two synthetic complexes and two biological metallocofactors are examined: a planar bis-渭-oxo bridged complex and a bent, bis-渭-oxo-渭-carboxylato bridge complex; the dimanganese catalase, which catalyzes the dismutation of H₂O₂ to H₂O and O₂, and the recently identified manganese/iron cofactor of the R2lox protein, a homologue of the small subunit of the ribonuclotide reductase enzyme (class 1c). High field (W-band) hyperfine EPR spectroscopies are demonstrated to be ideal methods to characterize the ¹⁷O magnetic interactions, allowing a magnetic fingerprint for the bridging oxygen ligand to be developed. It is shown that the 渭-oxo bridge motif displays a small positive isotropic hyperfine coupling constant of about +5 to +7 MHz and an anisotropic/dipolar coupling of 鈭? MHz. In addition, protonation of the bridge is correlated with an increase of the hyperfine coupling constant. Broken symmetry density functional theory is evaluated as a predictive tool for estimating hyperfine coupling of bridging species. Experimental and theoretical results provide a framework for the characterization of the oxygen bridge in Mn metallocofactor systems, including the water oxidizing cofactor of photosystem II, allowing the substrate/solvent interface to be examined throughout its catalytic cycle.