Rapatskiy Leonid, Ames William M, Pérez-Navarro Montserrat, Savitsky Anton, Griese Julia J, Weyhermüller Thomas, Shafaat Hannah S, Högbom Martin, Neese Frank, Pantazis Dimitrios A, Cox Nicholas
Max-Planck Institute for Chemical Energy , Stiftstr. 34-36 , Mülheim an der Ruhr, DE-45470 Germany.
Department of Biochemistry and Biophysics, Stockholm University , Stockholm SE-106 91, Sweden.
J Phys Chem B. 2015 Oct 29;119(43):13904-21. doi: 10.1021/acs.jpcb.5b04614. Epub 2015 Aug 26.
Multifrequency pulsed EPR data are reported for a series of oxygen bridged (μ-oxo/μ-hydroxo) bimetallic manganese complexes where the oxygen is labeled with the magnetically active isotope (17)O (I = 5/2). Two synthetic complexes and two biological metallocofactors are examined: a planar bis-μ-oxo bridged complex and a bent, bis-μ-oxo-μ-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 (17)O magnetic interactions, allowing a magnetic fingerprint for the bridging oxygen ligand to be developed. It is shown that the μ-oxo bridge motif displays a small positive isotropic hyperfine coupling constant of about +5 to +7 MHz and an anisotropic/dipolar coupling of -9 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.
报道了一系列氧桥连（μ-氧代/μ-羟基）双金属锰配合物的多频脉冲电子顺磁共振（EPR）数据，其中氧用具有磁活性的同位素（17）O（I = 5/2）标记。研究了两种合成配合物和两种生物金属辅因子：一种平面双μ-氧代桥连配合物和一种弯曲的双μ-氧代-μ-羧基桥连配合物；双锰过氧化氢酶，其催化H2O2歧化为H2O和O2，以及最近鉴定出的R2lox蛋白的锰/铁辅因子，核糖核苷酸还原酶（1c类）小亚基的同源物。高场（W波段）超精细EPR光谱被证明是表征（17）O磁相互作用的理想方法，能够建立桥连氧配体的磁指纹。结果表明，μ-氧代桥基序显示出约+5至+7 MHz的小正各向同性超精细耦合常数和-9 MHz的各向异性/偶极耦合。此外，桥的质子化与超精细耦合常数的增加相关。评估了破缺对称性密度泛函理论作为估计桥连物种超精细耦合的预测工具。实验和理论结果为表征锰金属辅因子系统中的氧桥提供了一个框架，包括光系统II的水氧化辅因子，从而能够在整个催化循环中研究底物/溶剂界面。
