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ENDOR Characterization of (N_2)Fe^(II)(μ-H)_2Fe^I(N_2)^−: A Spectroscopic Model for N_2 Binding by the Di-μ-hydrido Nitrogenase Janus Intermediate

Yang, Hao and Rittle, Jonathan and Marts, Amy R. and Peters, Jonas C. and Hoffman, Brian M. (2018) ENDOR Characterization of (N_2)Fe^(II)(μ-H)_2Fe^I(N_2)^−: A Spectroscopic Model for N_2 Binding by the Di-μ-hydrido Nitrogenase Janus Intermediate. Inorganic Chemistry, 57 (19). pp. 12323-12330. ISSN 0020-1669. PMCID PMC6649688. https://resolver.caltech.edu/CaltechAUTHORS:20180917-125103511

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Abstract

The biomimetic diiron complex 4-(N_2)_2, featuring two terminally bound Fe–N_2 centers bridged by two hydrides, serves as a model for two possible states along the pathway by which the enzyme nitrogenase reduces N_2. One is the Janus intermediate E4(4H), which has accumulated 4[e–/H+], stored as two [Fe–H–Fe] bridging hydrides, and is activated to bind and reduce N_2 through reductive elimination (RE) of the hydride ligands as H_2. The second is a possible RE intermediate. ^^1H and ^(14)N 35 GHz ENDOR measurements confirm that the formally Fe(II)/Fe(I) 4-(N_2)_2 complex exhibits a fully delocalized, Robin–Day type-III mixed valency. The two bridging hydrides exhibit a fully rhombic dipolar tensor form, T ≈ [−t, +t, 0]. The rhombic form is reproduced by a simple point-dipole model for dipolar interactions between a bridging hydride and its “anchor” Fe ions, confirming validity of this model and demonstrating that observation of a rhombic form is a convenient diagnostic signature for the identification of such core structures in biological centers such as nitrogenase. Furthermore, interpretation of the ^1H measurements with the anchor model maps the g tensor onto the molecular frame, an important function of these equations for application to nitrogenase. Analysis of the hyperfine and quadrupole coupling to the bound ^(14)N of N_2 provides a reference for nitrogen-bound nitrogenase intermediates and is of chemical significance, as it gives a quantitative estimate of the amount of charge transferred between Fe and coordinated N, a key element in N_2 activation for reduction.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1021/acs.inorgchem.8b02021DOIArticle
https://pubs.acs.org/doi/suppl/10.1021/acs.inorgchem.8b02021PublisherSupporting Information
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6649688PubMed CentralArticle
ORCID:
AuthorORCID
Yang, Hao0000-0002-8241-6231
Peters, Jonas C.0000-0002-6610-4414
Hoffman, Brian M.0000-0002-3100-0746
Alternate Title:ENDOR Characterization of (N2)FeII(μ-H)2FeI(N2)−: A Spectroscopic Model for N2 Binding by the Di-μ-hydrido Nitrogenase Janus Intermediate
Additional Information:© 2018 American Chemical Society. Received: July 20, 2018; Published: September 17, 2018. This work was supported by the NIH (GM 075757 to J.C.P) and the NSF (MCB 1515981 to B.M.H). We thank Dr. Peter Doan for insightful ENDOR discussions. The authors declare no competing financial interest.
Funders:
Funding AgencyGrant Number
NIHGM075757
NSFMCB-1515981
Issue or Number:19
PubMed Central ID:PMC6649688
Record Number:CaltechAUTHORS:20180917-125103511
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20180917-125103511
Official Citation:ENDOR Characterization of (N2)FeII(μ-H)2FeI(N2)−: A Spectroscopic Model for N2 Binding by the Di-μ-hydrido Nitrogenase Janus Intermediate. Hao Yang, Jonathan Rittle, Amy R. Marts, Jonas C. Peters, and Brian M. Hoffman. Inorganic Chemistry 2018 57 (19), 12323-12330. DOI: 10.1021/acs.inorgchem.8b02021
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:89675
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:17 Sep 2018 20:18
Last Modified:28 Feb 2020 15:45

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