Ligand effects on reactivity of hydride-decorated and reduced multi-iron compounds

标题：配体对双修饰和还原多铁化合物反应性的影响 摘要 金属簇辅因子为底物提供了许多潜在的结合方向， 经历化学转变。这对于激活小分子的簇辅因子尤其如此。 分子底物该提案的重点是铁钼辅因子的化学性质， 依赖于氘的固氮酶，催化八个电子和八个质子的还原， 二氮和两个质子以产生两当量的氨和一当量的二氢。当前 提出的通过这种酶将N2转化为NH3的机制使用了与 许多其它金属辅因子，例如桥连硫化物供体的质子化，金属辅因子的使用， 碳储存还原当量的潜力，以及碳和二氮在 终端或桥接模式。铁-钼辅因子如何结合氢化物供体， 双氮以及催化反应过程中的中间体是催化反应的基本方面。 机制，但仍不清楚。这就是本提案所要解决的知识差距。这项建议会 通过使用合成簇来实现这一目标，在合成簇中，底物（氮和二氮）可以结合在 桥接或终端协调模式，这反映了协调的灵活性， 这些底物上的铁-钼辅因子。作为调查的一部分，本提案将剖析 桥连配体的数目、身份和连接性调节底物配位。结果 在这个建议中产生的生物化学反应有更广泛的影响，特别是，脱落 关于控制多电子多质子氧化还原反应的生物催化的原理（例如， 光合作用中的水氧化，呼吸作用中的分子氧还原）。

Title: Ligand effects on reactivity of hydride-decorated and reduced multi-iron compounds Abstract Metal cluster cofactors provide substrates with many potential orientations to bind and subsequently undergo chemical transformations. This is particularly true for cluster cofactors that activate small molecule substrates. The focus of this proposal is on the chemistry of the iron-molybdenum cofactor in the molybdenum-dependent nitrogenases, which catalyzes the eight electron and eight proton reduction of dinitrogen and two protons to generate two equivalents of ammonia and one of dihydrogen. The current mechanism proposed for the conversion of N2 to NH3 by this enzyme uses concepts that are common to numerous other metal cofactors, such as the protonation of bridging sulfide donors, the use of metal hydrides to store reducing equivalents, and the potential to coordinate the hydrides and dinitrogen in either terminal or bridging modes. How the iron-molybdenum cofactor binds hydride donors and dinitrogen, as well as intermediates during the catalytic reaction, are fundamental aspects of the mechanism but remain unclear. This is the knowledge gap that this proposal addresses. This proposal will accomplish this goal by using synthetic clusters in which substrates (hydrides and dinitrogen) can bind in either bridging or terminal coordination modes, which mirrors the coordinative flexibility possible for these substrates on the iron-molybdenum cofactor. As part of this inquiry, this proposal will dissect how number, identity, and connectivity of bridging ligands modulate substrate coordination. The results generated in this proposal have broader implications for biochemical reactions, and specifically, shed light on the principles that govern biological catalysis of multi-electron multi-proton redox reactions (e.g., water oxidation in photosynthesis, dioxygen reduction in respiration).