Reiher Markus, Hess Bernd Artur
Lehrstuhl für Theoretische Chemie Universität Erlangen-Nürnberg, Egerlandstrasse 3 91058 Erlangen, Germany.
Chemistry. 2002 Dec 2;8(23):5332-9. doi: 10.1002/1521-3765(20021202)8:23<5332::AID-CHEM5332>3.0.CO;2-I.
The mechanism of biological dinitrogen reduction is still unsolved, and the structure of the biological reaction center, the FeMo cofactor with its seven iron atoms bridged by sulfur atoms, is too complicated for direct attack by current sophisticated quantum chemical methods. Therefore, iron-sulfur complexes with biologically compatible ligands are utilized as models for studying particular features of the reduction process: coordination energetics, thermodynamic stability of intermediates, relative stability of isomers of N2H2, end-on versus side-on binding of N2, and the role of states of different multiplicity at a single iron center. From the thermodynamical point of view, the crucial steps are dinitrogen binding and reduction to diazene, while especially the reduction of hydrazine to ammonia is not affected by the transition metal complex, because the complex-free reduction reaction is equally favored. Moreover, the abstraction of coordinated ammonia can be easily achieved and the complex is recovered for the next reduction cycle. Our results are discussed in the light of studies on various model systems in order to identify common features and to arrive at conclusions which are of importance for the biological mechanism.
生物固氮的机制尚未解决，生物反应中心的结构，即由硫原子桥接七个铁原子的铁钼辅因子，过于复杂，目前先进的量子化学方法难以直接对其进行研究。因此，具有生物相容性配体的铁硫配合物被用作研究还原过程特定特征的模型：配位能、中间体的热力学稳定性、N2H2异构体的相对稳定性、N2的端基结合与侧基结合，以及单个铁中心不同多重态状态的作用。从热力学角度来看，关键步骤是二氮的结合和还原为二氮烯，而特别地，肼还原为氨不受过渡金属配合物的影响，因为无配合物的还原反应同样有利。此外，可以很容易地实现配位氨的脱去，并且配合物可回收用于下一个还原循环。我们根据对各种模型系统的研究来讨论我们的结果，以便识别共同特征并得出对生物机制具有重要意义的结论。
