In the key enzyme for nitrogen fixation in nature, nitrogenase, the active site has a metal cluster with seven irons and one molybdenum bound by bridging sulfurs. Surprisingly there is also a carbon in the center of the cluster, with a role that is not known. A mechanism has been suggested experimentally, where two hydrides leave as a hydrogen molecule in the critical E₄ state. A structure with two hydrides, two protonated sulfurs and an unprotonated carbon has been suggested for this state. Rather recently, DFT calculations supported the experimental mechanism but found an active state where the central carbon is protonated all the way to CH₃. Even more recently, another DFT study was made that instead supported the experimentally suggested structure. In order to sort out the origin of these quite different computational results, additional calculations have here been performed using different DFT functionals. The conclusion from these calculations is very clear and shows no computational support for an unprotonated carbon in E₄.

中文翻译：

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是否为N ₄处于E ₄状态的未质子化碳提供了计算支持？

在自然界中用于固氮的关键酶中，固氮酶的活性位点具有一个金属簇，该簇中有7个铁和一个通过桥联硫键连接的钼。令人惊讶的是，在簇的中心还存在一个碳，其作用是未知的。实验上已经提出了一种机理，其中两个氢化物以氢分子的形式以临界E ₄状态离开。对于这种状态，已经提出了具有两个氢化物，两个质子化的硫和未质子化的碳的结构。相反，最近，DFT计算支持了实验机制，但发现了一个活动状态，其中中心碳一直质子化为CH ₃。甚至最近，又进行了另一项DFT研究，该研究支持了实验建议的结构。为了整理出这些完全不同的计算结果的来源，此处已使用不同的DFT功能执行了其他计算。这些计算得出的结论非常清楚，没有显示出对E _4中未质子化碳的计算支持。