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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >A New Nitrogenase Mechanism Using a CFe8S9 Model: Does H-2 Elimination Activate the Complex to N-2 Addition to the Central Carbon Atom?
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A New Nitrogenase Mechanism Using a CFe8S9 Model: Does H-2 Elimination Activate the Complex to N-2 Addition to the Central Carbon Atom?

机译：使用CFe8S9模型的新的固氮酶机制：H-2消除是否将复合物活化为N-2加到中央碳原子上？

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摘要

A truncated model of the FeMo cofactor is used to explore a new mechanism for the conversion of N-2 to NH3 by the nitrogenase enzyme. After four initial protonation/reduction steps, the H4CFe8S9 cluster has two hydrogen atoms attached to sulfur, one hydrogen bridging two iron centers and one hydrogen bonded to carbon. The loss of the CH and FeHFe hydrogens as molecular hydrogen activates the cluster to addition of N2 to the carbon center. This unique step takes place at a nearly planar four-coordinate carbon center and leads to an intermediate with a significantly weakened N-N bond. A hydrogen attached to a sulfur atom is then transferred to the distal nitrogen atom. Additional prontonation/reduction steps are modeled by adding a hydrogen atom to sulfur and locating the transition states for transfer to nitrogen. The first NH3 is lost in a thermal neutral step, while the second step is endothermic. The loss of H-2 activates the complex by reducing the barrier for N-2 addition by 3.5 kcal/mol. Since this is the most difficult step in the mechanism, reducing the barrier for this step justifies the "extra expense" of H-2 production.
机译：使用FeMo辅助因子的截短模型来探索由固氮酶将N-2转化为NH3的新机制。经过四个初始质子化/还原步骤后，H4CFe8S9簇具有两个与硫相连的氢原子，一个氢桥接两个铁中心和一个与碳键合的氢。 CH和FeHFe氢的损失是因为分子氢激活了团簇，从而将N2添加到碳中心。这个独特的步骤发生在几乎平坦的四坐标碳中心，并导致中间体的N-N键显着减弱。然后，附着在硫原子上的氢被转移到远端氮原子上。通过将氢原子添加到硫中并确定过渡态以转移到氮中，可以模拟其他质子化/还原步骤。第一个NH3在热中性步骤中损失，而第二个步骤则是吸热的。 H-2的损失通过将添加N-2的势垒降低3.5 kcal / mol来激活复合物。由于这是该机制中最困难的步骤，因此减少此步骤的障碍就可以证明H-2生产的“额外费用”是合理的。

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