Activation of N-O Bonds in Metal-NOx Complexes Related to Denitrifying Enzymes: Elucidation of Bioinorganic Pathways to Generate NO and HNO

反硝化金属酶是一种催化活性氧化态氮（NOx）相互转化的蛋白质，NOx是细胞中化学信号和地下水中硝酸盐污染物的来源。例如，硝酸盐肥料的过度使用已导致水生系统和含氮氧化物的饮用水水库饱和。其结果是生态失衡，浮游植物和藻类的过度生长导致水中含氧量低，最终导致大型水生生物死亡。有了这个奖项，化学部门的生命过程化学项目资助了乔治亚大学的Todd Harrop博士，研究铁和钴配合物作为反硝化金属酶的合成类似物，作为活性氮氧化物的来源、转化者和/或清除者。该项目阐明了这些金属酶类似物与环境和生理相关的氮氧化物的相互作用，以及这些物种的潜在相互转化。学生，包括那些来自代表性不足的少数群体的学生，将接受理解金属-氮氧化物化学的培训，这将建立设计原则和基本结构，电子，机械基准，以指导通过生物学转化氮氧化物的新方法的发现。该项目汇集了来自多个领域的合作者，包括生物化学、生物医学、环境、光谱/物理和理论科学。该项目与佐治亚大学Young Dawgs项目相结合，该项目为该州的高中生提供研究实习机会，并与Skype科学家项目相结合，作为与世界各地K-12教室的在线一般科学讨论。氮氧化物（NOx）的化学性质对各种生物和环境过程至关重要。事实上，氮氧化物种类亚硝酸盐（NO2-）和硝基（HNO）已经成为与缺氧信号事件相关的潜在调节剂，即一氧化氮（NO）的来源。此外，这两个物种都被证明在缺血预处理中起关键作用。然而，NO2-和HNO之间的联系尚不完全清楚，但它涉及金属位点，一些研究表明血红素可能执行这一任务。问题是血红素-铁如何进行亚硝酸盐到no（或HNO）的转化，从而产生稳定且高共价的Fe-NO键，以及哪些（如果有的话）其他生物信号制剂有助于这一任务？为了提高我们对与生物信号相关的M-NOx化学的理解，我们合成了低分子量配合物（受亚硝酸盐还原酶的启发），并对其进行了光谱表征：(i)揭示M-N(O)/N-O键激活的关键特征；（ii）获得在蛋白质中难以通过实验获得的M-NOx中间体；（iii）询问它们与其他关键小分子信号剂（硫醇）的反应；（iv）定义潜在的NOx连接/转化，作为生物学中类似转化的模型。所提出的M-NOx配合物的合成和反应性表明，在发现新的/稳定的NOx转化氧化还原催化剂方面取得了重大进展，这些催化剂可用于环境修复和哺乳动物生理学。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Denitrifying metalloenzymes are proteins that catalyze the interconversion of reactive oxidized forms of nitrogen (NOx), which are sources of chemical signals in cells and nitrate contaminants in groundwater. For example, the overuse of nitrate-based fertilizers has led to a saturation of aquatic systems as well as drinking water reservoirs with NOx. The result is ecological imbalance, with the associated overstimulated growth of phytoplankton and algae leading to low oxygen levels in water and ultimately death to larger aquatic organisms. With this award, the Chemistry of Life Processes Program in the Chemistry Division is funding Dr. Todd Harrop from the University of Georgia to study iron and cobalt complexes as synthetic analogues of denitrifying metalloenzymes as sources, converters, and/or scavengers of reactive NOx species. This project elucidates the interactions of these metalloenzyme analogues with environmentally and physiologically relevant NOx, and the potential interconversions of these species. Students, including those from underrepresented minority groups, are trained in the understanding of metal-NOx chemistry, which establishes design principles and fundamental structural, electronic, mechanistic benchmarks to guide the discovery of new ways to convert NOx through biology. The project brings together collaborators from across several fields, including the biochemical, biomedical, environmental, spectroscopic/physical, and theoretical sciences. This project is integrated with the UGA Young Dawgs program to provide research internships for high school students in the state and the Skype a Scientist program as an online general science discussion with K-12 classrooms around the world.The chemistry of nitrogen oxides (NOx) is critical to a variety of biological and environmental processes. Indeed, the NOx species nitrite (NO2-) and nitroxyl (HNO) have emerged as potential regulators associated with hypoxic signaling events, i.e., sources of nitic oxide (NO). Furthermore, both species have been shown to be critical in ischemic preconditioning. However, the link between NO2- and HNO is not entirely clear, but it involves metal sites and several studies suggest that hemes may perform this task. The question is how does heme-Fe perform the nitrite-to-NO (or HNO) conversion to result in an otherwise stable and highly covalent Fe-NO bond, and what (if any) other biological signaling agents assist in this task? To improve our understanding of M-NOx chemistry as it relates to biological signaling, low-molecular-weight coordination complexes (inspired by nitrite reductase) are synthesized and spectroscopically characterized to: (i) unravel features critical for M-N(O)/N-O bond activation, (ii) gain access to M-NOx intermediates that are challenging to experimentally achieve in the protein, (iii) interrogate their reactions with other critical small molecule signaling agents (thiols), and (iv) define potential NOx connections/conversions that serve as models for analogous transformations in biology. The synthesis and reactivity of the proposed M-NOx complexes represent significant advances toward the discovery of new/stable redox catalysts for NOx transformations that have applications in environmental remediation and mammalian physiology.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.