Molecular designs for controlling the local environments around metal ions.
Molecular designs for controlling the local environments around metal ions.
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DOI：
10.1021/acs.accounts.5b00212
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发表时间：
2015-08-18
影响因子：
18.3
通讯作者：
Borovik, A. S.
中科院分区：
文献类型：
--
作者：
Cook, Sarah A.;Borovik, A. S.
金属配合物的功能与它们所处的局部环境直接相关;已知局部环境（或次级配位球）的改变会导致金属中心的关键性质发生变化，从而影响反应性。非共价相互作用是调节二级配位球性质的最常见和最有影响力的力，这导致了在合成系统中通常难以实现的结构复杂性。利用金属蛋白活性位点的关键结构特征作为灵感，我们开发了分子系统，通过将氢键供体和受体结合到刚性配体支架中，在金属中心周围形成分子内氢键（H-键）。我们已经利用这些分子物种来探测生物分子氧活化和水氧化的机制方面。该帐户描述了不寻常的M-氧代和杂环化合物的稳定和表征。这些类型的物种在生物学中涉及一系列氧化过程，但由于其固有的反应性，通常难以研究。我们的H-键合配体系统使我们能够直接从O2的活化制备FeIII-氧代物种，O2随后被氧化形成具有S = 2自旋态的单体FeIV-氧代物种，类似于作为非血红素单加氧酶中的关键中间体提出的那些物种。我们还表明，一个单一的MnIII-氧代中心，从水制备的可以转化为高自旋MnV-氧代物种通过逐步氧化-一个过程，模仿光系统II的氧释放复合物（OEC）的氧化充电。目前的光合O-O键形成机制调用MnIV-oxyl物种，而不是等电子MnV-oxo系统作为关键氧化剂的计算研究的基础上。然而，没有实验信息支持Mn-氧基自由基的存在。因此，我们探测的量的自旋密度的氧化配体的配合物，使用EPR光谱结合氧-17标记。我们的研究结果表明，有一个显着量的自旋的氧化配体，但M-氧代键最好的描述为高度共价，并没有迹象表明，氧自由基的形成。这些结果提供了一种有趣的可能性，即高自旋的M-氧代配合物参与了生物学中O-O键的形成。配体的重新设计，将氢键接受单元（磺酰胺基）同时提供了一个金属离子结合口袋，相邻的氢键受体，和第二金属离子的辅助结合位点。这些特性使我们能够分离出一系列的铁III和锰III，其中第II族金属离子的二次配位范围内的配位的heterodynamic配合物。第二金属离子对初级金属中心的电子转移性质的影响的检查发现了意想不到的相似之处CaII和SrII离子的结果与相关的OEC。此外，发现第二金属离子的存在下，以防止分子内氧化的配体与O-原子转移试剂。
The functions of metal complexes are directly linked to the local environment in which they are housed; modifications to the local environment (or secondary coordination sphere) are known to produce changes in key properties of the metal centers that can affect reactivity. Non-covalent interactions are the most common and influential forces that regulate the properties of secondary coordination spheres, which leads to complexities in structure that are often difficult to achieve in synthetic systems. Using key architectural features from the active sites of metalloproteins as inspiration, we have developed molecular systems that enforce intramolecular hydrogen bonds (H-bonds) around a metal center via incorporation of H-bond donors and acceptors into rigid ligand scaffolds. We have utilized these molecular species to probe mechanistic aspects of biological dioxygen activation and water oxidation. This Account describes the stabilization and characterization of unusual M–oxo and heterobimetallic complexes. These types of species have been implicated in a range of oxidative processes in biology but are often difficult to study because of their inherent reactivity. Our H-bonding ligand systems allowed us to prepare an FeIII–oxo species directly from the activation of O2 that was subsequently oxidized to form a monomeric FeIV–oxo species with an S = 2 spin state, similar to those species proposed as key intermediates in non-heme monooxygenases. We also demonstrated that a single MnIII–oxo center that was prepared from water could be converted to a high spin MnV–oxo species via stepwise oxidation—a process that mimics the oxidative charging of the oxygen-evolving complex (OEC) of photosystem II. Current mechanisms for photosynthetic O–O bond formation invoke a MnIV–oxyl species rather than the isoelectronic MnV–oxo system as the key oxidant based on computational studies. However, there is no experimental information to support the existence of an Mn–oxyl radical. We therefore probed the amount of spin density on the oxido ligand of our complexes using EPR spectroscopy in conjunction with oxygen-17 labeling. Our findings showed that there is a significant amount of spin on the oxido ligand, yet the M–oxo bonds are best described as highly covalent and there is no indication that an oxyl radical is formed. These results offer the intriguing possibility that high spin M–oxo complexes are involved in O–O bond formation in biology. Ligand redesign to incorporate H-bond accepting units (sulfonamido groups) simultaneously provided a metal ion binding pocket, adjacent H-bond acceptors, and an auxiliary binding site for a second metal ion. These properties allowed us to isolate a series of heterobimetallic complexes of FeIII and MnIII in which a group II metal ion was coordinated within the secondary coordination sphere. Examination of the influence of the second metal ion on the electron transfer properties of the primary metal center revealed unexpected similarities between CaII and SrII ions—a result with relevance to the OEC. In addition, the presence of a second metal ion was found to prevent intramolecular oxidation of the ligand with an O-atom transfer reagent.
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影响因子：
15
作者：
Gupta, Rupal;Lacy, David C.;Bominaar, Emile L.;Borovik, A. S.;Hendrich, Michael P.
通讯作者：
Hendrich, Michael P.
影响因子：
56.9
作者：
Rittle, Jonathan;Green, Michael T.
通讯作者：
Green, Michael T.
影响因子：
56.9
作者：
Rohde, JU;In, JH;Que, L
通讯作者：
Que, L
影响因子：
15
作者：
Dey, Abhishek;Hocking, Rosalie K.;Solomon, Edward I.
通讯作者：
Solomon, Edward I.
影响因子：
56.9
作者：
Helm, Monte L.;Stewart, Michael P.;DuBois, Daniel L.
通讯作者：
DuBois, Daniel L.