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Binding of dinitrogen to an iron–sulfur–carbon site

Abstract

Nitrogenases are the enzymes by which certain microorganisms convert atmospheric dinitrogen (N2) to ammonia, thereby providing essential nitrogen atoms for higher organisms. The most common nitrogenases reduce atmospheric N2 at the FeMo cofactor, a sulfur-rich iron–molybdenum cluster (FeMoco)1,2,3,4,5. The central iron sites that are coordinated to sulfur and carbon atoms in FeMoco have been proposed to be the substrate binding sites, on the basis of kinetic and spectroscopic studies5,6,7. In the resting state, the central iron sites each have bonds to three sulfur atoms and one carbon atom. Addition of electrons to the resting state causes the FeMoco to react with N2, but the geometry and bonding environment of N2-bound species remain unknown5. Here we describe a synthetic complex with a sulfur-rich coordination sphere that, upon reduction, breaks an Fe–S bond and binds N2. The product is the first synthetic Fe–N2 complex in which iron has bonds to sulfur and carbon atoms, providing a model for N2 coordination in the FeMoco. Our results demonstrate that breaking an Fe–S bond is a chemically reasonable route to N2 binding in the FeMoco, and show structural and spectroscopic details for weakened N2 on a sulfur-rich iron site.

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Figure 1: N2 binding to iron in sulfur-rich environments.
Figure 2: N2 binding at an iron–sulfur–carbon site through Fe–S bond cleavage.
Figure 3: Fe–N2 complex supported by sulfur and carbon ligands.

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Acknowledgements

This work was supported by the National Institutes of Health (GM065313 to P.L.H.) and the Max Planck Society (E.B.). We thank A. Göbels for measurement of SQUID data and G. Brudvig for the use of an EPR spectrometer. Elemental analysis data were from the CENTC Elemental Analysis Facility at the University of Rochester, funded by the NSF (CHE-0650456), and we thank W. Brennessel for collecting these data. This work was supported in part by the facilities and staff of the Yale High Performance Computing Center, which was partially funded by the NSF (CNS 08-21132). We thank J. Mayer, N. Hazari, S. Bonyhady, N. Arnet, and C. MacLeod for constructive criticism on the manuscript.

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Authors

Contributions

I.Č. designed the iron–sulfur–carbon system for N2 binding, performed the laboratory experiments, and analysed data. B.Q.M. collected and interpreted crystallographic data. E.B. interpreted solid-state (SQUID) magnetic data. D.J.V. collected and fitted EPR data. P.L.H. supervised the research, and I.Č. and P.L.H. wrote the manuscript.

Corresponding author

Correspondence to Patrick L. Holland.

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The authors declare no competing financial interests.

Additional information

X-ray crystallographic data have been deposited in the Cambridge Crystallographic Data Centre (http://www.ccdc.cam.ac.uk/) with deposition numbers CCDC1402555–CCDC1402559.

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This file contains Supplementary Methods, Supplementary References and Supplementary Data (see Contents for details). (PDF 10994 kb)

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Čorić, I., Mercado, B., Bill, E. et al. Binding of dinitrogen to an iron–sulfur–carbon site. Nature 526, 96–99 (2015). https://doi.org/10.1038/nature15246

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