Analysis and Speculation

4) The occurrence of protonated bridging amides in 8 may be analogous to the behaviour of three-iron ferredoxins that undergo protonation upon reduction, presumably at bridging sulfides. The correspondence between Fe-NR and Fe-S chemistry extends to the redox activity of the core ligands, where the two-electron reduction of the N-N bond and the four-electron oxidative formation of the N=N bond are fully equivalent to sulfur-based half-reactions prevalent in 

I am grateful for the contributions of my co-workers whose names appear in the references. This work was made possible by the Beckman Foundation (Beckman Young Investigator Award) and the National Science Foundation (CAREER CHE-9984645). 

Rees and J. B. Howard, Curr. Opin. Chem. Biol., 2000,4, 559. 

Campobasso, S. W. Muchmore, T. V. Morgan and L. E. Mortenson, Molybdenum Enzymes, Cofactors, and Model Systems, American Chemical Society, Washington, DC, 1993, p. 186. 

Coucouvanis, J. Biol. Inorg. Chem., 1996,1, 594, and references therein. 

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