Fundamentals of Chemistry that Guide Formation of Sulfur-bridged Bi- and Multi-metallic Molecular Units

在化学系化学合成计划的支持下，德克萨斯农工大学的Marcetta Y.Darensburg教授和同事将研究分子，让化学家了解大自然选择硫来连接在生物中充当催化剂的结构中的金属。与人们可能在汽车催化转化器中发现的铂和铑等重、贵重/昂贵的金属不同，大自然必须依赖于金属在地球上的自然丰富分布。因此，富含地球的金属，如铁、镍和锰，被利用金属之间的协作性的分子基序所吸收。此外，它们在分子环境中的战略位置，以及反应物交付和产物释放的时机，使令人难以置信的反应在常温常压下很容易进行。连接的重要性对这些分子结合基序至关重要。硫是执行生命中一些最基本的反应的金属酶的关键成分。例子包括促进氢气生产、二氧化碳减少和氮气转化的催化剂。这些嵌入在蛋白质折叠中的分子催化剂是如何发挥作用的，这在很大程度上仍然是一个谜，这激励着化学家们在具有良好特征的小分子中寻找线索。这项工作将针对镍和铁在新的合成分子中的联系，这些分子配备了指示活性中心的“报告”分子。达伦斯堡团队将分析它们的结构和性质，监测电子一个接一个地添加或移除时的变化。他们将寻找和表征质子还原或合成的催化产物。这些基础研究是培养研究生、本科生和同事认识和欣赏连接生物和化学的科学的理想选择。在化学系化学合成计划的支持下，德克萨斯农工大学的Marcetta Y.Darensburg教授将制定一项合成化学计划，旨在提高对氧化还原处理酶中普遍存在的双金属结构的理解，包括二铁和镍铁氢酶。总体目标是了解两个(或多个)丰富的第一排金属如何分担双电子转换的负担，从而消除在自然催化和有机合成中对贵金属的需求。硫作为在金属或配体上具有氧化还原活性的金属络合物之间的桥梁，以及底物如何定位在反应中心上，这一普遍存在的问题引发了问题。这项工作将使用两个主要的经典“非无害”氧化还原活性配体，即一氧化氮(NO)和二硫杂环戊烯。达伦斯堡集团正在开发不含金属二硫酸盐配体作为过渡金属刘易斯酸接收器的双齿S供体，用于检测二亚铁三硝基中氧化还原水平的性质。该团队建议使用N-15同位素标记和二维红外光谱来监测两个S桥铁之间的电子和振动耦合，以确定受二铁络合物的氧化还原水平的影响。此外，氧化还原水平对观察到的NO配体在两个铁之间的扰乱的影响有望有助于我们理解硫桥双金属中金属之间的通信。以镍二硫杂环为受体的两种不同类型的离域配体对金属二硫醇化合物的协同作用将为探索分子间和/或分子内的磁猝灭和电子耦合提供了机会。对新双金属的性质的研究将提高我们对多金属生物无机酶活性部位的理解。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

With the support of the Chemical Synthesis program in the Division of Chemistry, Professor Marcetta Y. Darensbourg and coworkers of Texas A&M University will study molecules that inform chemists about Nature’s choice of sulfur to connect metals in structures that perform as catalysts in biology. In contrast to the heavy, precious/expensive metals such as platinum and rhodium that one might find in the catalytic converter of an automobile, Nature must rely on the natural abundance distribution of metals on earth. Consequently, earth-abundant metals such as iron, nickel, and manganese are taken up in molecular motifs that utilize cooperativity between metals. In addition, their strategic positioning within a molecular environment, and timing of delivery of reactants and release of products, renders incredible reactions that are facile at ordinary temperatures and pressures. The importance of connections is vital to these molecular-binding motifs. Sulfur is a key ingredient in metalloenzymes that perform some of the most fundamental reactions of life. Examples include catalysts that facilitate hydrogen production, carbon dioxide reduction, and nitrogen conversion. How these molecular catalysts, imbedded in protein folds, work remains largely a mystery that inspires chemists to search for clues in small, well characterized molecules. This work will target connections between nickel and iron in new synthetic molecules outfitted with “reporter” molecules that indicate reactive centers. The Darensbourg team will analyze their structures and properties, monitoring changes as electrons are added or removed one by one. They will search for and characterize products of catalysis of proton reduction or synthesis. These fundamental studies are ideal for training graduate and undergraduate students and coworkers to recognize and appreciate sciences that connect biology and chemistry. With the support of the Chemical Synthesis program in the Division of Chemistry, Professor Marcetta Y. Darensbourg of Texas A&M University will establish a synthetic chemistry plan that targets an improved understanding of bimetallic constructs prevalent in redox-processing enzymes including diiron and nickel-iron hydrogenases. The overall goal is to understand how two (or multiple) abundant first-row metals share the burden of 2-electron transformations, whereby obviating the need for noble metals in natural catalysis and organic synthesis. Questions arise from the ubiquitous mediation by sulfur as a bridge between metal complexes that have redox activity either at the metal or the ligands, and how substrates are positioned on the reactive centers. Two principal classic “non-innocent” redox-active ligands will be engaged for this work, namely nitric oxide (NO) and dithiolenes. The Darensbourg group is developing NO-containing metallodithiolate ligands as bidentate S-donors to a transition metal Lewis acid receiver for examination of properties of the redox levels in a diiron trinitrosyl. The team proposes to monitor the electronic and vibrational coupling between two S-bridged iron as affected by redox level of the diiron complex using N-15 isotopic labelling and two-dimensional infrared spectroscopy. In addition, the effect of redox level on the observed scrambling of the NO ligand between the two irons is expected to inform our understanding of communications between metals in the sulfur-bridged bimetallics. The concerted effect of two different types of delocalization ligands with a nickel-dithiolene as receiver to the metallodithiolates will offer an opportunity to explore inter- and/or intramolecular magnetic quenching and electronic coupling. Studies of the properties of the new bimetallics will improve our understanding of multimetallic bioinorganic enzyme active sites.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.