Electron Transfer in Catalytic Dinitrogen Reduction

In this article, the reasons for this mechanism in catalytic reduction of N2 will be considered, and results for electron transfer in biological N2 reduction and model synthetic systems will be compared. Hopefully, this consideration will lead to understanding how inert dinitrogen can be turned into a very active substrate readily reacting in solution in the presence of comparatively mild reducing agents. 

The mechanism and sequence of events that control delivery of protons and electrons to the FeMo cofactor during substrate reduction is not well understood in its particulars.8 It is believed that conformational change in MoFe-protein is necessary for electron transfer from the P-cluster to the M center (FeMoco) and that ATP hydrolysis and P release occurring on the Fe-protein drive the process. Hypothetically, P-clusters provide a reservoir of reducing equivalents that are transferred to substrate bound at FeMoco. Electrons are transferred one at a time from Fe-protein but the P-cluster and M center have electron buffering capacity, allowing successive two-electron transfers to, and protonations of, bound substrates.8 Neither component protein will reduce any substrate in the absence of its catalytic partner. Also, apoprotein (with any or all metal-sulfur clusters removed) will not reduce dinitrogen. 

Iron can be said to be the most chemically versatile of all the elements used by nature. It is essential for dioxygen uptake and transport in the vast majority of living systems, is ubiquitous in electron transfer relays and oxygen metabolism, is used widely as the catalytic center in enzymes catalyzing chemical changes as diverse as dinitrogen fixation, nitrate reduction, and isopenicillin-N-synthase, and is vital for DNA... 

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