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Yogendra S, Wilson DWN, Hahn AW, Weyhermüller T, Van Stappen C, Holland P, DeBeer S. Sulfur-Ligated [2Fe-2C] Clusters as Synthetic Model Systems for Nitrogenase. Inorg Chem 2023; 62:2663-2671. [PMID: 36715662 PMCID: PMC9930126 DOI: 10.1021/acs.inorgchem.2c03693] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2022] [Indexed: 01/31/2023]
Abstract
Metal clusters featuring carbon and sulfur donors have coordination environments comparable to the active site of nitrogenase enzymes. Here, we report a series of di-iron clusters supported by the dianionic yldiide ligands, in which the Fe sites are bridged by two μ2-C atoms and four pendant S donors.The [L2Fe2] (L = {[Ph2P(S)]2C}2-) cluster is isolable in two oxidation levels, all-ferrous Fe2II and mixed-valence FeIIFeIII. The mixed-valence cluster displays two peaks in the Mössbauer spectra, indicating slow electron transfer between the two sites. The addition of the Lewis base 4-dimethylaminopyridine to the Fe2II cluster results in coordination with only one of the two Fe sites, even in the presence of an excess base. Conversely, the cluster reacts with 8 equiv of isocyanide tBuNC to give a monometallic complex featuring a new C-C bond between the ligand backbone and the isocyanide. The electronic structure descriptions of these complexes are further supported by X-ray absorption and resonant X-ray emission spectroscopies.
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Affiliation(s)
- Sivathmeehan Yogendra
- Max
Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
| | - Daniel W. N. Wilson
- Department
of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
| | - Anselm W. Hahn
- Max
Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
| | - Thomas Weyhermüller
- Max
Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
| | - Casey Van Stappen
- Max
Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
| | - Patrick Holland
- Department
of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
| | - Serena DeBeer
- Max
Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
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2
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Wang CH, DeBeer S. Structure, reactivity, and spectroscopy of nitrogenase-related synthetic and biological clusters. Chem Soc Rev 2021; 50:8743-8761. [PMID: 34159992 DOI: 10.1039/d1cs00381j] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
The reduction of dinitrogen (N2) is essential for its incorporation into nucleic acids and amino acids, which are vital to life on earth. Nitrogenases convert atmospheric dinitrogen to two ammonia molecules (NH3) under ambient conditions. The catalytic active sites of these enzymes (known as FeM-cofactor clusters, where M = Mo, V, Fe) are the sites of N2 binding and activation and have been a source of great interest for chemists for decades. In this review, recent studies on nitrogenase-related synthetic molecular complexes and biological clusters are discussed, with a focus on their reactivity and spectroscopic characterization. The molecular models that are discussed span from simple mononuclear iron complexes to multinuclear iron complexes and heterometallic iron complexes. In addition, recent work on the extracted biological cofactors is discussed. An emphasis is placed on how these studies have contributed towards our understanding of the electronic structure and mechanism of nitrogenases.
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Affiliation(s)
- Chen-Hao Wang
- Max Planck Institute for Chemical Energy Conversion, Stiftstr. 34-36, 45470 Mülheim an der Ruhr, Germany.
| | - Serena DeBeer
- Max Planck Institute for Chemical Energy Conversion, Stiftstr. 34-36, 45470 Mülheim an der Ruhr, Germany.
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3
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Van Stappen C, Decamps L, Cutsail GE, Bjornsson R, Henthorn JT, Birrell JA, DeBeer S. The Spectroscopy of Nitrogenases. Chem Rev 2020; 120:5005-5081. [PMID: 32237739 PMCID: PMC7318057 DOI: 10.1021/acs.chemrev.9b00650] [Citation(s) in RCA: 115] [Impact Index Per Article: 28.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2019] [Indexed: 01/08/2023]
Abstract
Nitrogenases are responsible for biological nitrogen fixation, a crucial step in the biogeochemical nitrogen cycle. These enzymes utilize a two-component protein system and a series of iron-sulfur clusters to perform this reaction, culminating at the FeMco active site (M = Mo, V, Fe), which is capable of binding and reducing N2 to 2NH3. In this review, we summarize how different spectroscopic approaches have shed light on various aspects of these enzymes, including their structure, mechanism, alternative reactivity, and maturation. Synthetic model chemistry and theory have also played significant roles in developing our present understanding of these systems and are discussed in the context of their contributions to interpreting the nature of nitrogenases. Despite years of significant progress, there is still much to be learned from these enzymes through spectroscopic means, and we highlight where further spectroscopic investigations are needed.
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Affiliation(s)
- Casey Van Stappen
- Max Planck Institute for
Chemical Energy Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
| | - Laure Decamps
- Max Planck Institute for
Chemical Energy Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
| | - George E. Cutsail
- Max Planck Institute for
Chemical Energy Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
| | - Ragnar Bjornsson
- Max Planck Institute for
Chemical Energy Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
| | - Justin T. Henthorn
- Max Planck Institute for
Chemical Energy Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
| | - James A. Birrell
- Max Planck Institute for
Chemical Energy Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
| | - Serena DeBeer
- Max Planck Institute for
Chemical Energy Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
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4
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Nagelski AL, Fataftah MS, Bollmeyer MM, McWilliams SF, MacMillan SN, Mercado BQ, Lancaster KM, Holland PL. The influences of carbon donor ligands on biomimetic multi-iron complexes for N 2 reduction. Chem Sci 2020; 11:12710-12720. [PMID: 34094466 PMCID: PMC8163302 DOI: 10.1039/d0sc03447a] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
The active site clusters of nitrogenase enzymes possess the only examples of carbides in biology. These are the only biological FeS clusters that are capable of reducing N2 to NH4+, implicating the central carbon and its interaction with Fe as important in the mechanism of N2 reduction. This biological question motivates study of the influence of carbon donors on the electronic structure and reactivity of unsaturated, high-spin iron centers. Here, we present functional and structural models that test the impacts of carbon donors and sulfide donors in simpler iron compounds. We report the first example of a diiron complex that is bridged by an alkylidene and a sulfide, which serves as a high-fidelity structural and spectroscopic model of a two-iron portion of the active-site cluster (FeMoco) in the resting state of Mo-nitrogenase. The model complexes have antiferromagnetically coupled pairs of high-spin iron centers, and sulfur K-edge X-ray absorption spectroscopy shows comparable covalency of the sulfide for C and S bridged species. The sulfur-bridged compound does not interact with N2 even upon reduction, but upon removal of the sulfide it becomes capable of reducing N2 to NH4+ with the addition of protons and electrons. This provides synthetic support for sulfide extrusion in the activation of nitrogenase cofactors. High-spin diiron alkylidenes give insight into the electronic structure and functional relevance of carbon in the FeMoco active site of nitrogenase.![]()
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Affiliation(s)
| | | | - Melissa M. Bollmeyer
- Department of Chemistry and Chemical Biology
- Baker Laboratory
- Cornell University
- Ithaca
- USA
| | | | - Samantha N. MacMillan
- Department of Chemistry and Chemical Biology
- Baker Laboratory
- Cornell University
- Ithaca
- USA
| | | | - Kyle M. Lancaster
- Department of Chemistry and Chemical Biology
- Baker Laboratory
- Cornell University
- Ithaca
- USA
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5
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Speelman AL, Čorić I, Van Stappen C, DeBeer S, Mercado BQ, Holland PL. Nitrogenase-Relevant Reactivity of a Synthetic Iron-Sulfur-Carbon Site. J Am Chem Soc 2019; 141:13148-13157. [PMID: 31403298 DOI: 10.1021/jacs.9b05353] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Simple synthetic compounds with only S and C donors offer a ligation environment similar to the active site of nitrogenase (FeMoco) and thus demonstrate reasonable mechanisms and geometries for N2 binding and reduction in nature. We recently reported the first example of N2 binding at a mononuclear iron site supported by only S and C donors. In this work, we report experiments that examine the mechanism of N2 binding in this system. The reduction of an iron(II) tris(thiolate) complex with 1 equiv of KC8 leads to a thermally unstable intermediate, and a combination of Mössbauer, EPR, and X-ray absorption spectroscopies identifies it as a high-spin (S = 3/2) iron(I) species that maintains coordination of all three sulfur atoms. DFT calculations suggest that this iron(I) intermediate has a pseudotetrahedral geometry that resembles the S3C iron coordination environment of the belt iron sites in the resting state of the FeMoco. Further reduction to the iron(0) oxidation level under argon causes the dissociation of one of the thiolate donors and gives an η6-arene species which reacts with N2. Thus, in this system the loss of thiolate and binding of N2 require reduction beyond the iron(I) level to the iron(0) level. Further reduction of the iron(0)-N2 complex gives a reactive, formally iron(-I) species. Treatment of the putative iron(-I) complex with weak acids gives low yields of ammonia and hydrazine, demonstrating that these nitrogenase products can be generated from N2 at a synthetic Fe-S-C site. Catalytic N2 reduction is not observed, which is attributed to protonation of the supporting ligand and degradation of the complex via ligand dissociation. Identification of the challenges in this system gives insight into the design features needed for functional biomimetic complexes.
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Affiliation(s)
- Amy L Speelman
- Department of Chemistry , Yale University , 225 Prospect Street , New Haven , Connecticut 06520 , United States
| | - Ilija Čorić
- Department of Chemistry , Yale University , 225 Prospect Street , New Haven , Connecticut 06520 , United States
| | - Casey Van Stappen
- Max Planck Institute for Chemical Energy Conversion , Stiftstraße 34-36 , D-45470 Mülheim an der Ruhr , Germany
| | - Serena DeBeer
- Max Planck Institute for Chemical Energy Conversion , Stiftstraße 34-36 , D-45470 Mülheim an der Ruhr , Germany
| | - Brandon Q Mercado
- Department of Chemistry , Yale University , 225 Prospect Street , New Haven , Connecticut 06520 , United States
| | - Patrick L Holland
- Department of Chemistry , Yale University , 225 Prospect Street , New Haven , Connecticut 06520 , United States
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6
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DeBeer S. Advanced X-ray Spectroscopic Methods for Studying Iron-Sulfur-Containing Proteins and Model Complexes. Methods Enzymol 2017; 599:427-450. [PMID: 29746249 DOI: 10.1016/bs.mie.2017.09.008] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
In this chapter, a brief overview of X-ray spectroscopic methods that may be utilized to obtain insight into the geometric and electronic structure of iron-sulfur proteins is provided. These methods include conventional methods, such as metal and ligand K-edge X-ray absorption, as well as more advanced methods including nonresonant and resonant X-ray emission. In each section, the basic information content of the spectra is highlighted and important experimental considerations are discussed. Throughout the chapter, recent applications to iron-sulfur-containing models and proteins are highlighted.
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Affiliation(s)
- Serena DeBeer
- Max Planck Institute for Chemical Energy Conversion, Mülheim an der Ruhr, Germany.
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7
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Rees JA, Bjornsson R, Kowalska JK, Lima FA, Schlesier J, Sippel D, Weyhermüller T, Einsle O, Kovacs JA, DeBeer S. Comparative electronic structures of nitrogenase FeMoco and FeVco. Dalton Trans 2017; 46:2445-2455. [PMID: 28154874 PMCID: PMC5322470 DOI: 10.1039/c7dt00128b] [Citation(s) in RCA: 57] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2017] [Accepted: 01/25/2017] [Indexed: 12/17/2022]
Abstract
An investigation of the active site cofactors of the molybdenum and vanadium nitrogenases (FeMoco and FeVco) was performed using high-resolution X-ray spectroscopy. Synthetic heterometallic iron-sulfur cluster models and density functional theory calculations complement the study of the MoFe and VFe holoproteins using both non-resonant and resonant X-ray emission spectroscopy. Spectroscopic data show the presence of direct iron-heterometal bonds, which are found to be weaker in FeVco. Furthermore, the interstitial carbide is found to perturb the electronic structures of the cofactors through highly covalent Fe-C bonding. The implications of these conclusions are discussed in light of the differential reactivity of the molybdenum and vanadium nitrogenases towards various substrates. Possible functional roles for both the heterometal and the interstitial carbide are detailed.
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Affiliation(s)
- Julian A Rees
- Max Planck Institute for Chemical Energy Conversion, Stiftstr. 34-36, 45470 Mülheim an der Ruhr, Germany. and Department of Chemistry, University of Washington, Box 351700, Seattle, WA 98195-1700, USA.
| | - Ragnar Bjornsson
- Max Planck Institute for Chemical Energy Conversion, Stiftstr. 34-36, 45470 Mülheim an der Ruhr, Germany. and Science Institute, University of Iceland, Dunhagi 3, 107 Reykjavik, Iceland
| | - Joanna K Kowalska
- Max Planck Institute for Chemical Energy Conversion, Stiftstr. 34-36, 45470 Mülheim an der Ruhr, Germany.
| | - Frederico A Lima
- Max Planck Institute for Chemical Energy Conversion, Stiftstr. 34-36, 45470 Mülheim an der Ruhr, Germany. and Centro Nacional de Pesquisa em Energia e Materiais Brazilian Synchrotron Light Laboratory - LNLS Rua Giuseppe Máximo Scolfaro, 10.000 13083-970 Campinas SP, Brazil
| | - Julia Schlesier
- Institute for Biochemistry and BIOSS Centre for Biological Signalling Studies, Albert Ludwigs University Freiburg, Germany.
| | - Daniel Sippel
- Institute for Biochemistry and BIOSS Centre for Biological Signalling Studies, Albert Ludwigs University Freiburg, Germany.
| | - Thomas Weyhermüller
- Max Planck Institute for Chemical Energy Conversion, Stiftstr. 34-36, 45470 Mülheim an der Ruhr, Germany.
| | - Oliver Einsle
- Institute for Biochemistry and BIOSS Centre for Biological Signalling Studies, Albert Ludwigs University Freiburg, Germany.
| | - Julie A Kovacs
- Department of Chemistry, University of Washington, Box 351700, Seattle, WA 98195-1700, USA.
| | - Serena DeBeer
- Max Planck Institute for Chemical Energy Conversion, Stiftstr. 34-36, 45470 Mülheim an der Ruhr, Germany. and Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA
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8
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A Practical Guide to High-resolution X-ray Spectroscopic Measurements and their Applications in Bioinorganic Chemistry. Isr J Chem 2016. [DOI: 10.1002/ijch.201600037] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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9
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Ermert DM, Gordon JB, Abboud KA, Murray LJ. Nitride-Bridged Triiron Complex and Its Relevance to Dinitrogen Activation. Inorg Chem 2015; 54:9282-9. [DOI: 10.1021/acs.inorgchem.5b00825] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- David M. Ermert
- Department
of Chemistry, Center for Catalysis, University of Florida, Gainesville, Florida 32611, United States
| | - Jesse B. Gordon
- Department
of Chemistry, Center for Catalysis, University of Florida, Gainesville, Florida 32611, United States
| | - Khalil A. Abboud
- Department
of Chemistry, Center for Catalysis, University of Florida, Gainesville, Florida 32611, United States
| | - Leslie J. Murray
- Department
of Chemistry, Center for Catalysis, University of Florida, Gainesville, Florida 32611, United States
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10
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Donahue CM, McCollom SP, Forrest CM, Blake AV, Bellott BJ, Keith JM, Daly SR. Impact of Coordination Geometry, Bite Angle, and Trans Influence on Metal-Ligand Covalency in Phenyl-Substituted Phosphine Complexes of Ni and Pd. Inorg Chem 2015; 54:5646-59. [PMID: 25996554 DOI: 10.1021/ic503125b] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Despite the long-standing use of phosphine and diphosphine ligands in coordination chemistry and catalysis, questions remain as to their effects on metal-ligand bonding in transition metal complexes. Here we report ligand K-edge XAS, DFT, and TDDFT studies aimed at quantifying the impact of coordination geometry, diphosphine bite angle, and phosphine trans influence on covalency in M-P and M-Cl bonds. A series of four-coordinate NiCl2 and PdCl2 complexes containing PPh3 or Ph2P(CH2)nPPh2, where n = 1 (dppm), 2 (dppe), 3 (dppp), and 4 (dppb), was analyzed. The XAS data revealed that changing the coordination geometry from tetrahedral in Ni(PPh3)2Cl2 (1) to square planar in Ni(dppe)Cl2 (2) more than doubles the intensity of pre-edge features assigned to Ni-P and Ni-Cl 1s → σ* transitions. By way of comparison, varying the diphosphine in Pd(dppm)Cl2 (4), Pd(dppp)Cl2 (6), and Pd(dppb)Cl2 (7) yielded Pd-P 1s → σ* transitions with identical intensities, but a 10% increase was observed in the P K-edge XAS spectrum of Pd(dppe)Cl2 (5). A similar observation was made when comparing Ni(dppe)Cl2 (2) to Ni(dppp)Cl2 (3), and DFT and TDDFT calculations corroborated XAS results obtained for both series. Comparison of the spectroscopic and theoretical results to the diphosphine structures revealed that changes in M-P covalency were not correlated to changes in bite angles or coordination geometry. As a final measure, P and Cl K-edge XAS data were collected on trans-Pd(PPh3)2Cl2 (8) for comparison to the cis diphosphine complex Pd(dppe)Cl2 (5). Consistent with phosphine's stronger trans influence compared to chloride, a 35% decrease in the intensity of the Pd-P 1s → σ* pre-edge feature and a complementary 34% increase in Pd-Cl 1s → σ* feature was observed for 8 (trans) compared to 5 (cis). Overall, the results reveal how coordination geometry, ligand arrangement, and diphosphine structure affect covalent metal-phosphorus and metal-chloride bonding in these late transition metal complexes.
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Affiliation(s)
- Courtney M Donahue
- †Department of Chemistry, The University of Iowa, E331 Chemistry Building, Iowa City, Iowa 52242, United States
| | - Samuel P McCollom
- ‡Department of Chemistry, Colgate University, 13 Oak Drive, Hamilton, New York 13346, United States
| | - Chelsie M Forrest
- §Department of Chemistry, Western Illinois University, 1 University Circle, Macomb, Illinois 61455, United States
| | - Anastasia V Blake
- †Department of Chemistry, The University of Iowa, E331 Chemistry Building, Iowa City, Iowa 52242, United States
| | - Brian J Bellott
- §Department of Chemistry, Western Illinois University, 1 University Circle, Macomb, Illinois 61455, United States
| | - Jason M Keith
- ‡Department of Chemistry, Colgate University, 13 Oak Drive, Hamilton, New York 13346, United States
| | - Scott R Daly
- †Department of Chemistry, The University of Iowa, E331 Chemistry Building, Iowa City, Iowa 52242, United States
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11
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The role of X-ray spectroscopy in understanding the geometric and electronic structure of nitrogenase. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2014; 1853:1406-15. [PMID: 25486459 DOI: 10.1016/j.bbamcr.2014.11.027] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2014] [Revised: 11/22/2014] [Accepted: 11/24/2014] [Indexed: 10/24/2022]
Abstract
X-ray absorption (XAS) and X-ray emission spectroscopy (XES) provide element specific probes of the geometric and electronic structures of metalloprotein active sites. As such, these methods have played an integral role in nitrogenase research beginning with the first EXAFS studies on nitrogenase in the late 1970s. Herein, we briefly explain the information that can be extracted from XAS and XES. We then highlight the recent applications of these methods in nitrogenase research. The influence of X-ray spectroscopy on our current understanding of the atomic structure and electronic structure of iron molybdenum cofactor (FeMoco) is emphasized. Contributions of X-ray spectroscopy to understanding substrate interactions and cluster biosynthesis are also discussed. This article is part of a Special Issue entitled: Fe/S proteins: Analysis, structure, function, biogenesis and diseases.
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12
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Chandrasekaran P, Greene AF, Lillich K, Capone S, Mague JT, DeBeer S, Donahue JP. A Structural and Spectroscopic Investigation of Octahedral Platinum Bis(dithiolene)phosphine Complexes: Platinum Dithiolene Internal Redox Chemistry Induced by Phosphine Association. Inorg Chem 2014; 53:9192-205. [DOI: 10.1021/ic501273b] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- P. Chandrasekaran
- Department of Chemistry and Biochemistry, Lamar University, Beaumont, Texas 77710, United States
| | - Angelique F. Greene
- Department of Chemistry, Tulane University, 6400
Freret Street, New Orleans, Louisiana 70118, United States
| | - Karen Lillich
- Department of Chemistry, Tulane University, 6400
Freret Street, New Orleans, Louisiana 70118, United States
| | - Stephen Capone
- Department of Chemistry, Tulane University, 6400
Freret Street, New Orleans, Louisiana 70118, United States
| | - Joel T. Mague
- Department of Chemistry, Tulane University, 6400
Freret Street, New Orleans, Louisiana 70118, United States
| | - Serena DeBeer
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States
- Max Planck Institute for Chemical Energy Conversion, Stiftstrasse
34−36, D-45470 Mülheim an der Ruhr, Germany
| | - James P. Donahue
- Department of Chemistry, Tulane University, 6400
Freret Street, New Orleans, Louisiana 70118, United States
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