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H2 Formation Holds the Key to Opening the Fe Coordination Sites of Nitrogenase FeMo-cofactor for Dinitrogen Activation
preprintsubmitted on 28.09.2020, 18:12 and posted on 29.09.2020, 13:46 by Yong Li, Wan-Lu Li, Jin-Cheng Liu, Jun-Bo Lu, W. H. Eugen Schwarz, Lyudmila V. Moskaleva, Jun Li
The present quantum-mechanical and molecular-mechanics study reveals the crucial roles of H2 formation, of H2S shift and of N2 bond expansion in the nitrogenase process of the reduction of N2 to NH3. Proton and electron transfers to the Fe(C@Fe6S9)Mo unit of the FeMo-co complex weaken the Fe-S and Fe-H bonds and expose the Fe coordination sites, coupled with energy release due to H2 generation. Thereby the two sites Fe2 and Fe6 become prepared for stronger N2 adsorption, expanding and attenuating the ǀN≡Nǀ bond. After subsequent detachment of H2S from its Fe binding site into a holding site of the rearranged protein residue, the Fe6 site becomes completely unfolded, and the N2 triple bond becomes completely activated to an ‑N=N- double bond for easy subsequent hydrogenation to NH3. We explain in particular, why the obligatory H2 formation is an essential step in N2 adsorption and activation