Mechanistic insights into C-H bond activation in mononuclear non-heme iron enzymes from a combination of experiment and quantum chemistry

金属酶在代谢中起着重要的作用，特别是，它们能够利用“绿色”氧化剂分子氧来氧化烃类的未活化的脂肪族C-H键。[1，2]在原子水平上理解金属酶反应的催化机理将增强我们对进一步设计和合成新型低分子量“绿色”催化剂的认识。量子化学方法为这一重要的研究领域提供了关键的贡献：（1）计算潜在反应中间体的光谱参数并与实验测定的性质进行比较，对于X射线晶体学无法获得的短寿命物种的结构解析至关重要;（2）过渡态结构的优化，以便“连接”这些中间体并预测反应速率和动力学同位素效应;（3）这些中间体和过渡态的电子结构的定性分析提供了对催化机理的深入化学洞察。（4）组合分析为探索催化机理的复杂细节的结论性实验引发了新的想法。本研究旨在阐明牛磺酸的催化机制：α-酮戊二酸双加氧酶（TauD）、α-KG依赖的加氧酶/卤化酶（SyrB 2）和异青霉素N合酶（IPNS）。所有这些酶都以单核非血红素铁为中心，我们的美国项目合作伙伴对此进行了详细的实验研究。除了与以实验为导向的项目合作伙伴进行富有成效的互动外，我们还计划与专门研究大分子中氢原子转移反应的Hammes- Schiffer小组进行理论合作。这种协同的方法将使我们能够理解这些酶的电子和几何结构之间的关系，并在亚原子细节的酶活性。要完成的任务包括：1. 计算了它们中间体的光谱参数，并与实验结果进行了比较。2. 在势能面（PES）上定位过渡态，获得催化循环的详细能量信息。特别强调的是，将放在有关的概念，两个国家的反应性自旋态能量的重要课题。分析这些中间体和过渡态的电子结构，以了解原子水平上的催化机制。

Metalloenzymes play vital role in metabolism, in particular, they are capable to oxidize unactivated aliphatic C-H bonds of hydrocarbons employing the “green” oxidant dioxygen.[1,2] Understanding the catalytic mechanisms of metalloenzyme reactions at the atomic level will enhance our knowledge for further design and synthesis of novel low-molecular weight “green” catalysts. Quantum chemical approaches provide key contributions to this important field of investigation: (1) Calculation of the spectroscopic parameters of potential reaction intermediates and comparison with experimentally determined properties is vital for the structural elucidation of short lived species that are inaccessible to X-ray crystallography; (2) Optimization of the structures of transition states in order to “connect” these intermediates and to predict reaction rates and kinetic isotope effects; (3) Qualitative analysis of the electronic structures of these intermediates and transition states provides deep chemical insight into the catalytic mechanisms, (4) The combined analysis triggers new ideas for conclusive experiments that probe the intricate details of the catalytic mechanisms. This proposal is aimed at the elucidation of the catalytic mechanisms of Taurine:α- Ketoglutarate Dioxygenase (TauD), α-KG-dependent oxygenase/halogenase (SyrB2), and Isopenicillin N sythase (IPNS). All of these enzymes feature mononuclear nonheme iron centers, and were investigated in detail experimentally by our american project partners. In addition to the fruitful interaction with the experimentally oriented project partners we plan to engage in a theoretical collaboration with the Hammes- Schiffer group that is specialized in hydrogen atom transfer reactions in large molecules. This synergetic approach will enable us to understand the relationship between the electronic and geometric structure of these enzymes and their enzymatic activity in sub-atomic detail. Tasks to be completed include: 1. Calculation of spectroscopic parameters of their intermediates, verification of the results by comparison with experimental findings. 2. Location of transition states on the potential energy surfaces (PES), gaining detailed energetic information on the catalytic cycle. Particular emphasis will be laid on the important subject on spin-state energetics in relation to the concept of two-state reactivity. Analysis of electronic structure of these intermediates and transition states to understand the catalytic mechanism at the atomic level.