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Published December 7, 2021 | Supplemental Material + Published
Journal Article Open

Partial synthetic models of FeMoco with sulfide and carbyne ligands: Effect of interstitial atom in nitrogenase active site

Abstract

Nitrogen-fixing organisms perform dinitrogen reduction to ammonia at an Fe-M (M = Mo, Fe, or V) cofactor (FeMco) of nitrogenase. FeMco displays eight metal centers bridged by sulfides and a carbide having the MFe₇S₈C cluster composition. The role of the carbide ligand, a unique motif in protein active sites, remains poorly understood. Toward addressing how the carbon bridge affects the physical and chemical properties of the cluster, we isolated synthetic models of subsite MFe₃S₃C displaying sulfides and a chelating carbyne ligand. We developed synthetic protocols for structurally related clusters, [Tp*M'Fe₃S₃X]^(n−), where M' = Mo or W, the bridging ligand X = CR, N, NR, S, and Tp* = Tris(3,5-dimethyl-1-pyrazolyl)hydroborate, to study the effects of the identity of the heterometal and the bridging X group on structure and electrochemistry. While the nature of M' results in minor changes, the chelating, μ₃-bridging carbyne has a large impact on reduction potentials, being up to 1 V more reducing compared to nonchelating N and S analogs.

Additional Information

© 2021 National Academy of Sciences. Published under the PNAS license. Edited by Marcetta Y. Darensbourg, Texas A&M University, College Station, TX, and approved October 26, 2021 (received for review May 20, 2021). We are grateful to the NIH (R01-GM102687B to T.A.), Natural Sciences and Engineering Research Council of Canada (G.A.B.), the Resnick Sustainability Institute at Caltech (G.A.B.), and the NSF (Graduate Research Fellowships Program to A.G.S.) for funding. We thank the Beckman Institute and the Dow Next Generation Grant for instrumentation support. Michael Takase, Lawrence Henling, and Manar Shoshani are thanked for assistance with crystallography. Data Availability: Atomic coordinates and structure factors data have been deposited in the Cambridge Structural Database (CSD) of the Cambridge Crystallographic Data Centre (https://www.ccdc.cam.ac.uk/structures/). CSD reference numbers are as follows: 2084246 (1-Mo), 2081620 (2-W), 2084269 (2-Mo), 2081619 (3), 2081616 (4-W), 2084247 (4-Mo), 2081621 (5), 2081617 (6), 2081622 (7), and 2084054 (8). All other study data are included in the article and/or SI Appendix. Author contributions: L.N.V.L., G.A.B., A.G.S., and T.A. designed research; L.N.V.L., G.A.B., and A.G.S. performed research; L.N.V.L., G.A.B., A.G.S., and T.A. analyzed data; L.N.V.L., G.A.B., A.G.S., and T.A. wrote the paper; and T.A. mentored researchers. The authors declare no competing interest. This article is a PNAS Direct Submission. This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.2109241118/-/DCSupplemental.

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Additional details

Created:
August 22, 2023
Modified:
October 23, 2023