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

金属酶在新陈代谢中起着至关重要的作用，特别是它们能够利用“绿色”氧化剂氧气氧化未活化的碳氢化合物的脂肪族C-H键。[1，2]在原子水平上了解金属酶反应的催化机理将增进我们对新型低分子量“绿色”催化剂的设计和合成的认识。量子化学方法对这一重要研究领域做出了关键贡献：(1)计算潜在反应中间体的光谱参数并与实验确定的性质进行比较，对于阐明X射线结晶学无法获得的短寿命物种的结构至关重要；(2)优化过渡态的结构以便“连接”这些中间体并预测反应速率和动力学同位素效应；(3)对这些中间体和过渡态的电子结构进行定性分析，使人们能够深入了解催化机理；(4)联合分析为探索催化机理的错综复杂的细节的结束性实验提供新的思路。该建议旨在阐明牛磺酸的催化机理：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合成酶(IPNS)。所有这些酶都以单核非血红素铁中心为特征，并由我们的美国项目合作伙伴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卓有成效的互动外，我们还计划与专门从事大分子氢原子转移反应的Hammes-Schiffer小组进行理论合作。这种协同方法将使我们能够在亚原子细节上了解这些酶的电子结构和几何结构与其酶活性之间的关系。需要完成的工作包括：1.中间体光谱参数的计算，并与实验结果进行比较验证。2.过渡态在势能面(PES)上的位置，获得关于催化循环的详细能量信息。我们将特别强调与两态反应性概念有关的自旋态能量学这一重要课题。分析这些中间体和过渡态的电子结构，从原子水平上了解催化机理。

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.