Functional LnFe-NxHy Models of Biological N2 Fixation

描述（由申请人提供）：生物固氮的功能性LnFe-NxHy模型固氮酶（N2 ase）是一种介导生物固氮的金属酶，对维持生命至关重要。因此，固氮酶的研究吸引了生物和化学界的密切关注。尽管如此，固氮酶在环境条件下促进氮的生物还原的机制仍然是一个迷人的和未解决的问题。我们研究的广泛目标是评估单个铁位点能够在合成模型系统中介导催化N2还原的机制，并由此扩展到生物学中。本研究拟设计和研究仿生Fe-NxHy模型配合物来实现这一目标。我们的实验方法强调功能，而不是结构，铁钼辅因子（FeMoco）的忠实模型。将开发低分子量Fe-NxHy络合物以探索可能容纳二氮和其他NxHy官能的局部4-和5-配位几何结构中的铁位点。我们将这些几何形状与FeMoco的Fe-NxHy中间体相关。通过类比的模式，生物催化O2还原，两个限制机制将进行评估。首先是一个交替的机制，连续质子化发生在远端和近端的Fe-N？N亚基以交替的方式（例如，Fe-N=NH？Fe-NH=NH？Fe-NH-NH2？铁氨氨Fe-NH 2 + NH 3）。第二种是远端机制，其中远端N原子处的完全质子化先于近端N原子处的质子化（例如，Fe-N2 + 3 e- + 3 H+？菲？N + NH3）。我们将使用合成的模型复合物来理解Fe-NxHy物种的核性、局部几何形状和电子结构如何控制它们的相对稳定性和反应模式。目的是将这些知识应用于设计可以促进催化N2酶活性的模型系统。无论在FeMoco的氮还原的精确机制，其最终的解决方案将需要从辅因子的光谱数据的比较得到的明确定义的模型复合物的相关数据。我们将与专门从事FeMoco光谱研究的研究人员合作进行此类比较。总之，功能Fe-NxHy模型化学提出将继续发挥关键作用，同时目前的生物化学，光谱和理论模型研究，旨在解开生物固氮的化学机制。

DESCRIPTION (provided by applicant): Functional LnFe-NxHy Models of Biological N2 Fixation Nitrogenase (N2ase) is a metalloenzyme that mediates biological nitrogen fixation and is essential to sustain life. As such, the study of nitrogenase attracts intense scrutiny among the biology and chemistry communities. Nonetheless, the mechanism by which nitrogenase enzymes promote the biological reduction of nitrogen under ambient conditions remains a fascinating and unsolved problem. The broad goal of our research is to evaluate the mechanisms by which a single iron site is able to mediate catalytic N2 reduction in synthetic model systems and, by extension, in biology. The proposed program is to design and study biomimetic Fe-NxHy model complexes to address this goal. Our experimental approach stresses functionally, rather than structurally, faithful models of the iron-molybdenum cofactor (FeMoco). Low molecular weight Fe-NxHy complexes will be developed to explore iron sites in local 4- and 5-coordinate geometries that may accommodate dinitrogen and other NxHy functionalites. We posit these geometries as relevant to Fe-NxHy intermediates of the FeMoco. By analogy to the modes of biocatalytic O2 reduction, two limiting mechanisms will be evaluated. The first is an alternating mechanism, where successive protonations occur at the distal and proximal N-atoms of the Fe-N?N subunit in an alternating fashion (e.g., Fe-N=NH ? Fe-NH=NH ? Fe-NH-NH2 ? Fe-NH2-NH2 ? Fe-NH2 + NH3). The second is a distal mechanism, where complete protonation at the distal N-atom precedes protonation at the proximal N-atom (e.g., Fe-N2 + 3 e- + 3 H+? Fe?N + NH3). We will use synthetic model complexes to understand how the nuclearity, local geometry, and electronic structure of Fe- NxHy species control their relative stabilities and reactivity patterns. The intent is to apply this knowledge to design model systems that can facilitate catalytic N2ase activity. Regardless of the precise mechanism for nitrogen reduction at the FeMoco, its ultimate solution will require comparison of spectroscopic data from the cofactor to related data obtained for well-defined model complexes. We will collaborate with researchers that specialize in spectroscopic studies of the FeMoco to make such comparisons. In sum, the functional Fe-NxHy model chemistry proposed will continue to play a critical role alongside current biochemical, spectroscopic, and theoretical model studies aimed at unraveling the chemical mechanism of biological nitrogen fixation.