Controlling the Reactivity of a Metal-Hydroxo Adduct with a Hydrogen Bond
Controlling the Reactivity of a Metal-Hydroxo Adduct with a Hydrogen Bond
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具有氢键的金属-羟基加合物的反应性控制
DOI：
10.1021/jacs.1c06199
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发表时间：
2021-09-08
影响因子：
15
通讯作者：
Jackson, Timothy A.
中科院分区：
文献类型：
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作者：
Opalade, Adedamola A.;Hessefort, Logan;Jackson, Timothy A.
锰脂氧合酶（MnLOX）和锰超氧化物歧化酶（MnSOD）利用单核Mn中心来实现它们的催化反应。在氧化的锰-III状态下，每个酶的活性位点包含一个羟基配体，X射线晶体结构暗示这个羟基配体和顺式羧酸配体之间存在氢键。虽然氢键是酶活性位点的共同特征，但这种特定的羟基-羧酸相互作用的重要性相对未被探索。在本研究中，我们研究了一对锰-III-羟配合物，不同的是一个单一的官能团。这些配合物之一，[Mn-III（OH）（PaPy 2N）]（+），含有能够与羟基配体形成分子内氢键的萘啶基部分。第二种配合物[Mn-III（OH）（PaPy（2）Q）]（+）含有不允许任何分子内氢键的喹啉基部分。这些配合物的光谱表征支持共同的结构，但与扰动[Mn-III（OH）（PaPy 2N）]（+），与氢键一致。使用具有活化的O-H键的各种底物的动力学研究表明，[Mn-III（OH）（PaPy（2）Q）]（+）比[Mn-III（OH）（PaPy（2）Q）]（+）更具反应性，速率增强15-100倍。使用DFT计算对这些反应的热力学贡献的详细分析表明，前一种络合物是显着更基本的。这种增加的碱度抵消了该络合物的更负的还原电位，导致[Mn-II（OH 2）（PaPy 2N）]（+）产物中更强的O-H BDFE。因此，[Mn-III（OH）（PaPy（2）Q）]（+）和[Mn-III（OH）（PaPy 2N）]（+）之间的反应性差异可以基于热力学考虑来理解，热力学考虑受到后一种络合物形成分子内氢键的能力的强烈影响。
The enzymes manganese lipoxygenase (MnLOX) and manganese superoxide dismutase (MnSOD) utilize mononuclear Mn centers to effect their catalytic reactions. In the oxidized Mn-III state, the active site of each enzyme contains a hydroxo ligand, and X-ray crystal structures imply a hydrogen bond between this hydroxo ligand and a cis carboxylate ligand. While hydrogen bonding is a common feature of enzyme active sites, the importance of this particular hydroxo-carboxylate interaction is relatively unexplored. In this present study, we examined a pair of Mn-III-hydroxo complexes that differ by a single functional group. One of these complexes, [Mn-III(OH)(PaPy2N)](+), contains a naphthyridinyl moiety capable of forming an intramolecular hydrogen bond with the hydroxo ligand. The second complex, [Mn-III(OH)(PaPy(2)Q)](+), contains a quinolinyl moiety that does not permit any intramolecular hydrogen bonding. Spectroscopic characterization of these complexes supports a common structure, but with perturbations to [Mn-III(OH)(PaPy2N)](+), consistent with a hydrogen bond. Kinetic studies using a variety of substrates with activated O-H bonds, revealed that [Mn-III(OH)(PaPy2N)](+) is far more reactive than [Mn-III(OH)(PaPy(2)Q)](+), with rate enhancements of 15-100-fold. A detailed analysis of the thermodynamic contributions to these reactions using DFT computations reveals that the former complex is significantly more basic. This increased basicity counteracts the more negative reduction potential of this complex, leading to a stronger O-H BDFE in the [Mn-II(OH2)(PaPy2N)](+) product. Thus, the differences in reactivity between [Mn-III(OH)(PaPy(2)Q)](+) and [Mn-III(OH)(PaPy2N)](+) can be understood on the basis of thermodynamic considerations, which are strongly influenced by the ability of the latter complex to form an intramolecular hydrogen bond.