Functional LnFe-Nx Models of Biological N2 Fixation

生物 N2 固定的功能性 LnFe-Nx 模型

• 批准号: 6865169
• 负责人: Jonas C Peters
• 金额: $ 27.59万
• 依托单位: CALIFORNIA INSTITUTE OF TECHNOLOGY
• 依托单位国家: 美国
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-02-01 至 2010-01-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6865169
• 关键词: binding sites; biomimetics; cofactor; electron transport; enzyme mechanism; enzyme model; enzyme structure; iron compounds; nitrogen fixation; nitrogenase; structural biology

DESCRIPTION (provided by applicant): Nitrogenase (N2ase) is a metalloenzyme that mediates biological nitrogen fixation and as such is essential to sustained life. Understanding the chemical mechanism by which N2ase-mediated nitrogen reduction occurs is therefore of general interest. The proposed program is to study biomimetic LnFe-Nx model complexes that will help to evaluate a mechanistic scheme that stresses a single Fe-Nx binding site in the FeMo cofactor (FeMoco) of N2ase. The experimental design focuses on functional rather than structural models of the FeMoco. Low molecular weight LnFe-Nx complexes will be developed to isolate a single iron site in either a tetrahedral or a trigonal bipyramidal geometry while at the same time preserving one binding site to accommodate dinitrogen and various other Nx functionalities. The Ln donor scaffolds will incorporate phosphorous and/or sulfur donor groups to render the LnFe species sufficiently electron-rich to bind relatively inert N2. By analogy to the mode of biocatalytic O2 reduction (FeII-O2 + 2 e-+ 2 H+ -> FeIV= O + H2O), a mechanistic sequence for N2 reduction that proceeds through a terminal nitride intermediate (Fel-N2 + 3 e-+ 3 H+ -> FeIV=(N + NH3) will be explored. To this end each of the critical intermediates envisaged for the complete cycle will be generated and studied. These intermediates will include Fel-N2, Fell-N=NH, Felll=N-NH2, FeIV = N, FeIII(NH, FeII-NH2, and Fel-NH3 species. Of further interest will be to understand how the local geometry and electronic structure of the LnFe-Nx species control their relative stabilities and reactivity patterns at their Fe-Nx linkages. The intent is to then use this knowledge to further design model systems that can facilitate catalytic N2ase activity. To accomplish these collective goals will require the physical and theoretical characterization of each type of Fe-Nx species, a mechanistic understanding of each of the stepwise transformations that pertain to the proposed cycle, and exploratory catalytic studies that will expose promising model systems that successfully mediate nitrogen fixation.

说明(申请人提供)：固氮酶(N2ase)是一种金属酶，可以调节生物固氮，因此对维持生命是必不可少的。因此，了解N2ase介导的氮还原发生的化学机制是人们普遍感兴趣的。该计划是为了研究仿生LnFe-NX模型络合物，这将有助于评估一种机制方案，即强调N2ase的FEMO辅因子(FeMoco)中的单一Fe-Nx结合位点。实验设计的重点是FeMoco的功能模型，而不是结构模型。低分子量LnFe-NX络合物将被开发来分离四面体或三角双锥构型中的单一铁位置，同时保留一个结合位置以适应氮和其他各种NX官能团。Ln给体支架将结合磷和/或硫给体基团，使LnFe物种具有足够丰富的电子，以结合相对惰性的氮气。通过类似于生物催化还原O2的模式(FeII-O2+2e-+2H+&gt；FeIV=O+H2O；FeIV=O+H2O)，将探索通过终端氮化物中间体(FeL-N2+3e-+3H+&gt；FeIV=(N+NH3))进行氮气还原的机理序列。为此目的，将生成和研究为整个周期设想的每一种关键中间体。这些中间体将包括FeL-N、Fell-N=NH、FELL=N-NH2、FeIV=N、FeIII(NH、FeII-NH2和FeEL-NH3物种)。更有兴趣的是了解LnFe-NX物种的局部几何结构和电子结构如何控制它们在Fe-NX键上的相对稳定性和反应模式。其目的是随后利用这一知识进一步设计能够促进催化N2ase活性的模型系统。为了实现这些集体目标，将需要对每种类型的Fe-NX物种进行物理和理论表征，从机理上了解与所提议的循环有关的每一种逐步转化，并进行探索性催化研究，以揭示成功调节固氮的有希望的模型系统。