Chemical Reactivity and Redox Behavior of Heme-Nitrogen Oxide Derivatives

许多因素导致天气和环境的变化，其中之一是大气中含氮气体一氧化二氮（N2O）积累的增加。细菌和真菌利用复杂的金属酶从天然原料一氧化氮（NO）中生成N2O，但这一过程的基本化学机制尚不清楚。因此，迫切需要探索和了解全球氮循环的这一组成部分，特别是金属在调节这种对环境和农业具有重要意义的氮氧化物气体的产生和消耗中所起的作用。合作者George Richter-Addo博士和Michael Shaw博士研究了复杂细菌和真菌金属酶的非蛋白化学类似物，以探测这些生物体的N2O形成和NOx利用。特别是，该团队正在沿着观察到的反应途径制备、分离和表征不稳定中间体。这些研究使我们能够更好地了解这些气体是如何产生和控制的，以及如何改善作物生长所需肥料中的基本元素氮。合作团队结合了博士环境（在俄克拉何马大学）和主要的本科环境（在南伊利诺伊大学爱德华兹维尔），为不同群体的学生提供高水平的培训。该小组还积极向有风险的高中生和公众介绍现代科学。乔治·里克特-阿多博士参加了一个专为市中心高中学生设计的暑期项目，这些孩子在学业上有很高的失败风险。Michael Shaw博士制作了适合残疾人的在线讲座视频，从而代表了向传统上难以接触到的代表性不足的群体进行科学宣传的途径。血红素蛋白参与了与全球变暖相关的一氧化氮（NO）到一氧化二氮（N2O）的转化，以及与农业氮同化和亚硝化胁迫相关的无机氮氧化物到有机氮氧化物的转化。这两个过程都很重要，但它们的基本化学途径尚不清楚，因此阻碍了全球n循环中这些成分的化学进一步发展。在美国国家科学基金会化学分部化学结构、动力学和机制b项目的资助下，George Richter-Addo博士（俄克拉何马大学）和Michael Shaw博士（南伊利诺伊大学爱德华兹维尔分校）的合作研究小组正在确定导致合成卟啉系统中结合NO配体化学反应的因素，该系统模拟了细菌和真菌中涉及N2O和/或有机氮氧化物生成的含铁酶。合作团队正在确定有利于铁-NO卟啉中结合的NO配体亲核攻击的实验条件，并促进N2O的形成（通过H-N键形成；真菌N2O途径）和有机氮氧化物的生成（通过C-N/N-N/S-N键形成）。它们还决定了激活亚铁-NO卟啉中结合的NO配体以形成N-N键和产生N2O（细菌N2O途径）的需求。该团队利用化学合成、光谱学和先进的光谱电化学相结合，并辅以密度泛函理论计算进行这项研究。这个合作小组积极向处于危险中的高中生和公众介绍现代科学。除了为大一新生（化学入门）和研究生（电化学）开发新的教育材料外，该团队还积极参与了一个为不同种族和经济条件较差的市中心高中学生设计的暑期项目。该小组还在适合残疾人的丰富的多层灵活的在线环境中制作在线讲座视频，从而代表了向传统上难以接触到的代表性不足的群体进行科学宣传的途径。研究人员还制作和策划了几个免费的电化学Labview软件程序，供全球通用。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。

Many factors contribute to changes in the weather and the environment, one of which is the increased accumulation of the nitrogen-containing gas nitrous oxide (N2O) in the atmosphere. Bacteria and fungi utilize complex metalloenzymes to generate N2O from the natural starting material nitric oxide (NO), but the fundamental chemical mechanisms for this process are not understood. Therefore, there is an urgent need to probe and understand this component of the global N-cycle, in particular, the role that metals play in mediating the production and consumption of such NOx gases of environmental and agricultural importance. Collaborators Dr. George Richter-Addo and Dr. Michael Shaw study non-protein chemical analogues of complex bacterial and fungal metalloenzymes to probe N2O formation and NOx utilization by these organisms. In particular, the team is preparing, isolating, and characterizing unstable intermediates along observed reaction pathways. These studies allow for a better understanding of how these gases are produced and controlled, and how nitrogen, an essential element in fertilizer required for crop growth, can be improved. The collaborative team combines a Ph.D. environment (at the University of Oklahoma) and a primarily undergraduate environment (at Southern Illinois University Edwardsville) to provide high-level training to a diverse group of students. The team is also active in introducing at-risk high school students and the general public to modern science. Dr. George Richter-Addo participates in a summer program designed for inner city high school kids at high risk for failure in academic programs. Dr. Michael Shaw produces on-line lecture videos suitable for individuals with disabilities, thus representing an avenue of science outreach to a traditionally hard-to-reach underrepresented group.Heme proteins are involved in the nitric oxide (NO) to nitrous oxide (N2O) conversion of relevance to global warming, and in the inorganic-NOx to organo-NOx conversions of relevance to agricultural N-assimilation and nitrosative stress. Both processes are important, but their fundamental chemical pathways are not well understood, thus preventing further development of the chemistry of these components of the global N-cycle. With funding from the Chemical Structure, Dynamics and Mechanisms-B Program of the NSF Chemistry Division, the collaborative research team of Dr. George Richter-Addo (University of Oklahoma) and Dr. Michael Shaw (Southern Illinois University Edwardsville) is determining the factors that lead to chemical reactivity of the bound NO ligand in synthetic porphyrin systems that model heme-containing enzymes in bacteria and fungi involved in N2O and/or organo-NOx generation. The collaborative team is determining the experimental conditions that favor nucleophilic attack of the bound NO ligand in ferric-NO porphyrins and promote N2O formation (via H-N bond formation; fungal N2O pathway) and organo-NOx generation (via C-N/N-N/S-N bond formation). They are also determining the requirements for activating the bound NO ligand in ferrous-NO porphyrins towards N-N bond formation and N2O production (bacterial N2O pathway). The team utilizes a combination of chemical synthesis, spectroscopy, and advanced spectroelectrochemistry, complemented by density functional theory calculations for this research. The collaborative team is active in introducing at-risk high school students and the general public to modern science. In addition to developing new educational materials at the freshman (introductory chemistry) and graduate (electrochemistry) levels, the team actively participates in a summer program designed for ethnically diverse and economically disadvantaged inner-city high school children. The team also produces on-line lecture videos in a rich multilayer flexible online environment suitable for individuals with disabilities, thus representing an avenue of science outreach to a traditionally hard-to-reach underrepresented group. The investigators also produce and curate several freely available electrochemistry Labview software programs for general worldwide use.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.