Modeling the photosynthetic water oxidation complex:: Activation of water by controlled deprotonation and incorporation into a tetranuclear manganese complex
Modeling the photosynthetic water oxidation complex:: Activation of water by controlled deprotonation and incorporation into a tetranuclear manganese complex
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DOI：
10.1021/ja9730573
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发表时间：
1998-06-17
影响因子：
15
通讯作者：
Christou, G
中科院分区：
文献类型：
--
作者：
Aromí, G;Wemple, MW;Christou, G
阐明的结构和作用机制的主要是羧酸根连接，氧化物桥接的Mn 4簇在水氧化中心（WOC）的植物和蓝藻是当前的极大兴趣。1，2这个簇结合，去质子化，并氧化耦合两个H2O分子产生O2，但这种转换的确切细节尚不清楚。最近，我们发展了Mn Ⅲ 3 Mn Ⅳ配合物[Mn_4 O_3X（O_2CMe）_3（dbm）_3]（X ~-）Cl ~-，Br ~-，PhCO_2 ~-，MeCO_2 ~-; dbmH）二苯甲酰基甲烷）3，其含有[Mn 4 O3]氧化物桥连的三角锥状Mn 4核，该核是与天然位点上最近的EXAFS数据一致的拓扑结构之一，4，它既有短的（2.7毫米）和长的（3.3毫米）Mn... Mn分离。一个主要的目标是利用这些模型复合物，以获得结构和机制的见解与它的辅因子（Cl-，Br-，NO3-等）的天然簇的相互作用，抑制剂（F-、NH3、RNH 2、ROH）和底物（H2O）; 1我们已经表明，例如，[Mn 4 O3（O2 CMe）4（dbm）3]（1）容易与F-源反应，得到[Mn 4 O3 F（O2 CMe）3（dbm）3]。3c了解Mn 4簇结合，去质子化和氧化H2O分子的方式是主要目标，我们正试图使用模型络合物以逐步的方式实现这一点，这可能会允许中间体被识别，从而提供对这种转化如何进行的见解。在目前的工作中，我们报告说，1将自发反应与水在温和的，非强制性的条件下，导致后者的去质子化，并将其纳入核心。该反应代表了H2O的受控活化，并被提议作为O2释放路径上关键的第一步沿着步骤的模型系统。1与H2O和MeOH的反应性通过使用[Mn 4 O3（O2 CCD 3）4-（dbm）3]（1a）的2 H NMR光谱方便地监测;这避免了dbm共振的复杂存在，并给出了比1H NMR光谱更尖锐的共振。除了CHDCl 2杂质的信号外，室温下1a的光谱还显示了分别来自µ-O2 CCD 3和独特µ3-O2 CCD 3组的36.8和66.1 ppm处的两个信号，积分比为3：1（图1，顶部）。添加蒸馏的MeOH导致这两个信号的降低，
Elucidating the structure and mechanism of action of the predominantly carboxylate-ligated, oxide-bridged Mn4 cluster at the water oxidation center (WOC) of plants and cyanobacteria is of great current interest. 1, 2 This cluster binds, deprotonates, and oxidatively couples two H2O molecules to yield O2, but the precise details of this transformation are unclear. Recently, we have developed preparative methodology to the MnIII 3MnIV complexes [Mn4O3X (O2CMe) 3 (dbm) 3](X-) Cl-, Br-, PhCO2-, MeCO2-; dbmH) dibenzoylmethane) 3 containing the [Mn4O3] oxidebridged trigonal pyramidal Mn4 core that is one of the topologies consistent with recent EXAFS data on the native site, 4 which has both short (∼ 2.7 Å) and long (∼ 3.3 Å) Mn... Mn separations. A major objective is to employ these model complexes to obtain structural and mechanistic insights into the interaction of the native cluster with its cofactors (Cl-, Br-, NO3-, etc.), inhibitors (F-, NH3, RNH2, ROH), and substrate (H2O); 1 we have shown, for example, that [Mn4O3 (O2CMe) 4 (dbm) 3](1) readily reacts with a F-source to give [Mn4O3F (O2CMe) 3 (dbm) 3]. 3c Understanding the means by which a Mn4 cluster binds, deprotonates, and oxidizes H2O molecules is the primary objective, and we are attempting to use model complexes to achieve this in a stepwise fashion that might allow intermediates to be identified and thus provide insights into how such a transformation might proceed. In the present work, we report that 1 will spontaneously react with H2O under mild, nonforcing conditions leading to deprotonation of the latter and its incorporation into the core. This reaction represents a controlled activation of H2O and is proposed as a model system for the crucial first steps along the path to O2 evolution.The reactivity of 1 with H2O and MeOH was conveniently monitored by 2H NMR spectroscopy using [Mn4O3 (O2CCD3) 4-(dbm) 3](1a); this avoids the complicating presence of dbm resonances and gives sharper resonances than 1H NMR spectroscopy. In addition to the signal for CHDCl2 impurity, the spectrum of 1a at room temperature shows two signals at 36.8 and 66.1 ppm in a 3: 1 integration ratio from the µ-O2CCD3 and unique µ3-O2CCD3 groups, respectively (Figure 1, top). Addition of distilled MeOH causes a decrease in these two signals and