Low-Coordinate Synthetic Models for Nitrogenase Activity

固氮酶活性的低坐标合成模型

• 批准号: 8075476
• 负责人: PATRICK L HOLLAND
• 金额: $ 30.54万
• 依托单位: UNIVERSITY OF ROCHESTER
• 依托单位国家: 美国
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-04-01 至 2014-04-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8075476
• 关键词: Active Sites; Amaze; Ammonia; Binding; Bioinorganic Chemistry; Biological; Calculi; Carbon monoxide dehydrogenase; Chemicals; Communities; Complex; Coupling; Crystallization; Crystallography; Data; Databases; Electrochemistry; Electron Nuclear Double Resonance; Electron Transport; Electrons; Environment; Enzymes; Funding; Goals; Hydrazine; Hydrogenase; Iron; Kinetics; Knowledge; Lead; Learning; Life; Ligands; Link; Modeling; Molybdenum; Mononuclear; Nitrogen; Nitrogen Fixation; Nitrogenase; Nuclear; Organic solvent product; Oxidation-Reduction; Pathway interactions; Process; Property; Proteins; Reaction; Research; Roentgen Rays; Role; Scientist; Site; Solid; Solubility; Specific qualifier value; Spectrum Analysis; Structure; Sulfides; Sulfur; Support Groups; Work; absorption; adduct; analog; base; biological systems; biotin synthase; catalyst; chemical reaction; chemical synthesis; cold temperature; diazene; electron nuclear double resonance spectroscopy; fascinate; functional group; functional mimics; insight; novel; oxidation; planetary Atmosphere; public health relevance; small molecule

DESCRIPTION (provided by applicant): Nitrogenases are vitally important enzymes that perform an amazing chemical reaction, the reduction of N2 to ammonia. In nitrogenases, iron-sulfur clusters catalyze multielectron reductions of small molecules, a role that differs from the more common role of iron-sulfur clusters as electron-transfer sites that avoid bond-making and bond-breaking reactions. Little is known about the mechanism of substrate reduction by nitrogenases. Our guiding hypothesis is that nitrogenases and other reactive iron-sulfur cluster enzymes generate a transient open site on an iron atom for substrate binding. Recent spectroscopic work on iron- molybdenum nitrogenase strongly suggests that the mechanism involves binding of N2 to iron, and involves iron-hydride species. However, there are no chemical precedents for iron-sulfur clusters that have an open site, or for iron-sulfur clusters with a hydride. Examples of N2 binding to high-spin iron are rare and understudied. Synthetic compounds with these features are needed to evaluate the feasibility of the proposed functional groups on iron-sulfur clusters, to establish the spectroscopic signatures of these functional groups, and to learn whether their reactivity is consistent with the enzymatic products. In the proposed research, we will create synthetic iron-containing compounds with each of these functionalities: unsaturated iron-sulfur clusters, iron-sulfide-hydride clusters, and iron-N2 complexes. The isolation and characterization of these compounds is made possible by the use of very bulky supporting groups. The bulky groups also facilitate crystallization, and enhance solubility in organic solvents that can be used at low temperature. Crystallography, kinetic studies, electrochemistry, and reactivity will be used to elucidate the atomic-level detail of the elementary steps of small-molecule binding and reduction. The synthetic complexes will be evaluated by ENDOR, infrared, Raman, M"ssbauer, and X- ray absorption spectroscopies to provide a link between the structures of novel model compounds and the known data for nitrogenases. We anticipate that the proposed work will lead to the first solid precedents for reaction pathways in nitrogenases. Although much is known about the mechanisms of multielectron oxidation reactions in bioinorganic chemistry, the knowledge about multielectron biological reductions is much less. Therefore, there is fundamental importance in learning how the iron-sulfide cluster in nitrogenase binds and transforms small molecules that are essential for life. In the long run, understanding the mechanisms of small-molecule reduction in biological systems may also lead to new catalysts for use in chemical synthesis. PUBLIC HEALTH RELEVANCE: Enzymes that contain iron and sulfur produce many of the molecules that are essential for life, but are not understood well. The iron-sulfur enzyme nitrogenase converts unreactive nitrogen in the atmosphere into forms that can be used, and life as we know it is dependent upon this process of "nitrogen fixation." However, the scientific community does not yet know how nitrogenase works. This project aims to show the principles underlying the mechanism of nitrogen fixation, which may also lead to new catalysts for transforming organic and inorganic molecules.

描述（由申请人提供）：氮酶是一种至关重要的酶，它可以进行惊人的化学反应，将N2还原为氨。在氮酶中，铁硫团簇催化小分子的多电子还原，这一作用不同于铁硫团簇更常见的作用，它是电子转移位点，避免了成键和断键反应。对氮酶还原底物的机制了解甚少。我们的指导假设是，氮酶和其他活性铁硫簇酶在铁原子上产生一个用于底物结合的瞬时开放位点。最近对铁钼氮酶的光谱研究表明，其机制涉及到N2与铁的结合，并涉及到铁氢化物。然而，没有化学先例表明铁硫团簇有一个开放的位置，或者铁硫团簇有一个氢化物。N2与高自旋铁结合的例子很少，研究还不够充分。需要合成具有这些特征的化合物来评估所提出的官能团在铁硫簇上的可行性，建立这些官能团的光谱特征，并了解它们的反应性是否与酶促产物一致。在提议的研究中，我们将合成具有这些功能的含铁化合物：不饱和铁硫团簇，铁硫化物-氢化物团簇和铁n2配合物。这些化合物的分离和表征可以通过使用非常庞大的支持基团来实现。庞大的基团还有助于结晶，并提高在低温下可使用的有机溶剂中的溶解度。晶体学、动力学研究、电化学和反应学将用于阐明小分子结合和还原的基本步骤的原子水平细节。合成的配合物将通过ENDOR，红外，拉曼，M ' ssbauer和X射线吸收光谱进行评估，以提供新模型化合物结构与已知氮酶数据之间的联系。我们预计，所提出的工作将导致第一个坚实的先例，反应途径在氮酶。虽然生物无机化学中多电子氧化反应的机理已经了解很多，但对多电子生物还原反应的认识却很少。因此，了解氮酶中的硫化铁簇如何结合和转化对生命至关重要的小分子是至关重要的。从长远来看，了解生物系统中小分子还原的机制也可能导致用于化学合成的新催化剂。