1
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Fritsche P, Geyer L, Czernetzki C, Hierlmeier G. Coordination-induced reductive elimination from a titanium(IV) complex. Chem Commun (Camb) 2024. [PMID: 39046231 DOI: 10.1039/d4cc02500h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/25/2024]
Abstract
Diamidopyridine-supported titanium dibenzyl complexes undergo coordination-induced C-C reductive elimination upon addition of alkynes and quantitative formation of titanacyclopentadienes. The distinct radical mechanism of this reductive mechanism gives new insights into C-C bond formation with titanium.
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Affiliation(s)
- Paul Fritsche
- Julius-Maximilians-Universität Würzburg, Institut für Anorganische Chemie, Am Hubland, 97074 Würzburg, Germany.
| | - Lucia Geyer
- Julius-Maximilians-Universität Würzburg, Institut für Anorganische Chemie, Am Hubland, 97074 Würzburg, Germany.
| | - Corinna Czernetzki
- Julius-Maximilians-Universität Würzburg, Institut für Anorganische Chemie, Am Hubland, 97074 Würzburg, Germany.
| | - Gabriele Hierlmeier
- Julius-Maximilians-Universität Würzburg, Institut für Anorganische Chemie, Am Hubland, 97074 Würzburg, Germany.
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2
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Duletski OL, Platz D, Pollock CJ, Mosquera MA, Arulsamy N, Mock MT. Dinitrogen activation at chromium by photochemically induced Cr II-C bond homolysis. Chem Commun (Camb) 2024; 60:7029-7032. [PMID: 38894651 DOI: 10.1039/d4cc02387k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/21/2024]
Abstract
The synthesis of the organochromium(II) complexes [POCOPtBu]Cr(R) (R = p-Tol, Bn) is reported. Exposure of [POCOPtBu]Cr(Bn) to visible light promoted homolytic Cr-CBn bond cleavage and formed {[POCOPtBu]Cr}2(η1:η1μ-N2) via a putative [POCOPtBu]Cr(I) species.
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Affiliation(s)
- Olivia L Duletski
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT 59717, USA.
| | - Duncan Platz
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT 59717, USA.
| | - Charlie J Pollock
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT 59717, USA.
| | - Martín A Mosquera
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT 59717, USA.
| | | | - Michael T Mock
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT 59717, USA.
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3
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Le LN, Joyce JP, Oyala PH, DeBeer S, Agapie T. Highly Activated Terminal Carbon Monoxide Ligand in an Iron-Sulfur Cluster Model of FeMco with Intermediate Local Spin State at Fe. J Am Chem Soc 2024; 146:5045-5050. [PMID: 38358932 PMCID: PMC10910499 DOI: 10.1021/jacs.3c12025] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2023] [Revised: 01/29/2024] [Accepted: 01/30/2024] [Indexed: 02/17/2024]
Abstract
Nitrogenases, the enzymes that convert N2 to NH3, also catalyze the reductive coupling of CO to yield hydrocarbons. CO-coordinated species of nitrogenase clusters have been isolated and used to infer mechanistic information. However, synthetic FeS clusters displaying CO ligands remain rare, which limits benchmarking. Starting from a synthetic cluster that models a cubane portion of the FeMo cofactor (FeMoco), including a bridging carbyne ligand, we report a heterometallic tungsten-iron-sulfur cluster with a single terminal CO coordination in two oxidation states with a high level of CO activation (νCO = 1851 and 1751 cm-1). The local Fe coordination environment (2S, 1C, 1CO) is identical to that in the protein making this system a suitable benchmark. Computational studies find an unusual intermediate spin electronic configuration at the Fe sites promoted by the presence the carbyne ligand. This electronic feature is partly responsible for the high degree of CO activation in the reduced cluster.
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Affiliation(s)
- Linh N.
V. Le
- Division
of Chemistry and Chemical Engineering, California
Institute of Technology, Pasadena, California 91125, United States
| | - Justin P. Joyce
- Max
Planck Institute for Chemical Energy Conversion, Stiftstraße 34-36, 45470 Mülheim an der Ruhr, Germany
| | - Paul H. Oyala
- Division
of Chemistry and Chemical Engineering, California
Institute of Technology, Pasadena, California 91125, United States
| | - Serena DeBeer
- Max
Planck Institute for Chemical Energy Conversion, Stiftstraße 34-36, 45470 Mülheim an der Ruhr, Germany
| | - Theodor Agapie
- Division
of Chemistry and Chemical Engineering, California
Institute of Technology, Pasadena, California 91125, United States
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4
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Mörsdorf JM, Ballmann J. Coordination-Induced Radical Generation: Selective Hydrogen Atom Abstraction via Controlled Ti-C σ-Bond Homolysis. J Am Chem Soc 2023; 145:23452-23460. [PMID: 37861658 DOI: 10.1021/jacs.3c05748] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2023]
Abstract
A method for the generation of transient alkyl radicals via homolytic Ti-C bond cleavage was developed by employing a tailor-made organotitanium half-cage complex. In contrast to established metal-mediated radical initiation protocols via thermal or photochemical M-C σ-bond homolysis, radical formation is triggered solely by coordination of a solvent molecule (thf) to a titanium(IV) center. During the reaction, the nonstabilized alkyl radical is formed along with a persistent titanium(III) metalloradical, thus taming the former transient radical (persistent radical effect). Radical coupling and hydrogen atom abstraction (HAT) reactions have been explored not only experimentally but also computationally and by means of kinetic analysis. Exploiting these findings led to the development of selective HAT transformations, for example, with 9,10-dihydroanthracene. Deuterium labeling studies using selectively deuterated alkyls and 9,10-dihydroanthracene-d4 confirmed a radical pathway, which was underpinned by developing a radical-radical cross-coupling reaction for transferring the alkyl radical to a stable Sn-centered radical. To set the stage for an application in organic synthesis, a 5-endo-trig radical cyclization based on our methodology was established, and a dihydroxylated sesquiterpene was thus prepared in high diastereomeric excess.
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Affiliation(s)
- Jean-Marc Mörsdorf
- Anorganisch-Chemisches Institut, Universität Heidelberg, Im Neuenheimer Feld 276, D-69120 Heidelberg, Germany
| | - Joachim Ballmann
- Anorganisch-Chemisches Institut, Universität Heidelberg, Im Neuenheimer Feld 276, D-69120 Heidelberg, Germany
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5
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Boucher DG, Pendergast AD, Wu X, Nguyen ZA, Jadhav RG, Lin S, White HS, Minteer SD. Unraveling Hydrogen Atom Transfer Mechanisms with Voltammetry: Oxidative Formation and Reactivity of Cobalt Hydride. J Am Chem Soc 2023; 145:17665-17677. [PMID: 37530748 DOI: 10.1021/jacs.3c03815] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/03/2023]
Abstract
The utility of transition metal hydride catalyzed hydrogen atom transfer (MHAT) has been widely demonstrated in organic transformations such as alkene isomerization and hydrofunctionalization reactions. However, the highly reactive nature of the hydride and radical intermediates has hindered mechanistic insight into this pivotal reaction. Recent advances in electrochemical MHAT have opened up the possibility for new analytical approaches for mechanistic diagnosis. Here, we report a voltammetric interrogation of Co-based MHAT reactivity, describing in detail the oxidative formation and reactivity of the key Co-H intermediate and its reaction with aryl alkenes. Insights from cyclic voltammetry and finite element simulations help elucidate the rate-limiting step as metal hydride formation, which we show to be widely tunable based on ligand design. Voltammetry is also suggestive of the formation of Co-alkyl intermediates and a dynamic equilibrium with the reactive neutral radical. These mechanistic studies provide information for the design of future hydrofunctionalization reactions, such as catalyst and silane choice, the relative stability of metal-alkyl species, and how hydrofunctionalization reactions utilize Co-alkyl intermediates. In summary, these studies establish an important template for studying MHAT reactions from the perspective of electrochemical kinetic frameworks.
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Affiliation(s)
- Dylan G Boucher
- Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, United States
| | - Andrew D Pendergast
- Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, United States
| | - Xiangyu Wu
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States
| | - Zachary A Nguyen
- Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, United States
| | - Rohit G Jadhav
- Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, United States
| | - Song Lin
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States
| | - Henry S White
- Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, United States
| | - Shelley D Minteer
- Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, United States
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6
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Bostelaar TM, Brown AC, Sridharan A, Suess DLM. A general method for metallocluster site-differentiation. NATURE SYNTHESIS 2023; 2:740-748. [PMID: 39055685 PMCID: PMC11271975 DOI: 10.1038/s44160-023-00286-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/20/2022] [Accepted: 03/02/2023] [Indexed: 07/27/2024]
Abstract
The deployment of metalloclusters in applications such as catalysis and materials synthesis requires robust methods for site-differentiation: the conversion of clusters with symmetric ligand spheres to those with unsymmetrical ligand spheres. However, imparting precise patterns of site-differentiation is challenging because, compared with mononuclear complexes, the ligands bound to clusters exert limited spatial and electronic influence on one another. Here, we report a method that employs sterically encumbering ligands to bind to only a subset of a cluster's coordination sites. Specifically, we show that homoleptic, phosphine-ligated Fe-S clusters undergo ligand substitution with N-heterocyclic carbenes (NHCs) to give heteroleptic clusters in which the resultant clusters' site-differentiation patterns are encoded by the steric profile of the incoming NHC. This method affords access to every site-differentiation pattern for cuboidal [Fe4S4] clusters and can be extended to other cluster types, particularly in the stereoselective synthesis of site-differentiated Chevrel-type [Fe6S8] clusters.
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Affiliation(s)
- Trever M Bostelaar
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Alexandra C Brown
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Arun Sridharan
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Daniel L M Suess
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA
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7
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Heuer A, Coste SC, Singh G, Mercado BQ, Mayer JM. A Guide to Tris(4-Substituted)-triphenylmethyl Radicals. J Org Chem 2023; 88:9893-9901. [PMID: 37403939 PMCID: PMC10367072 DOI: 10.1021/acs.joc.3c00658] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2023] [Indexed: 07/06/2023]
Abstract
Triphenylmethyl (trityl, Ph3C•) radicals have been considered the prototypical carbon-centered radical since their discovery in 1900. Tris(4-substituted)-trityls [(4-R-Ph)3C•] have since been used in many ways due to their stability, persistence, and spectroscopic activity. Despite their widespread use, existing synthetic routes toward tris(4-substituted)-trityl radicals are not reproducible and often lead to impure materials. We report here robust syntheses of six electronically varied (4-RPh)3C•, where R = NMe2, OCH3, tBu, Ph, Cl, and CF3. The characterization reported for the radicals and related compounds includes five X-ray crystal structures, electrochemical potentials, and optical spectra. Each radical is best accessed using a stepwise approach from the trityl halide, (RPh)3CCl or (RPh)3CBr, by controllably removing the halide with subsequent 1e- reduction of the trityl cation, (RPh)3C+. These syntheses afford consistently crystalline trityl radicals of high purity for further studies.
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Affiliation(s)
| | | | - Gurjot Singh
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Brandon Q. Mercado
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - James M. Mayer
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
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8
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Skeel BA, Suess DLM. Exploiting Molecular Symmetry to Quantitatively Map the Excited-State Landscape of Iron-Sulfur Clusters. J Am Chem Soc 2023; 145:10376-10395. [PMID: 37125463 DOI: 10.1021/jacs.3c02412] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
Cuboidal [Fe4S4] clusters are ubiquitous cofactors in biological redox chemistry. In the [Fe4S4]1+ state, pairwise spin coupling gives rise to six arrangements of the Fe valences ("valence isomers") among the four Fe centers. Because of the magnetic complexity of these systems, it has been challenging to understand how a protein's active site dictates both the arrangement of the valences in the ground state as well as the population of excited-state valence isomers. Here, we show that the ground-state valence isomer landscape can be simplified from a six-level system in an asymmetric protein environment to a two-level system by studying the problem in synthetic [Fe4S4]1+ clusters with solution C3v symmetry. This simplification allows for the energy differences between valence isomers to be quantified (in some cases with a resolution of <0.1 kcal/mol) by simultaneously fitting the VT NMR and solution magnetic moment data. Using this fitting protocol, we map the excited-state landscape for a range of clusters of the form [(SIMes)3Fe4S4-X/L]n, (SIMes = 1,3-dimesityl-imidazol-4,5-dihydro-2-ylidene; n = 0 for anionic, X-type ligands and n = +1 for neutral, L-type ligands) and find that a single ligand substitution can alter the relative ground-state energies of valence isomers by at least 103 cm-1. On this basis, we suggest that one result of "non-canonical" amino acid ligation in Fe-S proteins is the redistribution of the valence electrons in the manifold of thermally populated excited states.
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Affiliation(s)
- Brighton A Skeel
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Daniel L M Suess
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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9
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Brown AC, Suess DLM. Valence Localization in Alkyne and Alkene Adducts of Synthetic [Fe 4S 4] + Clusters. Inorg Chem 2023; 62:1911-1918. [PMID: 35704768 PMCID: PMC9751231 DOI: 10.1021/acs.inorgchem.2c01353] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Reported herein are alkyne and alkene adducts of synthetic [Fe4S4]+ clusters that model intermediates and inhibitor-bound states in enzymes involved in isoprenoid biosynthesis. Treatment of the N-heterocyclic carbene-ligated cluster [(IMes)3Fe4S4(OEt2)][BArF4] (IMes = 1,3-dimesitylimidazol-2-ylidene; [BArF4]- = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate) with phenylacetylene (PhCCH) or cis-cyclooctene (COE) results in displacement of the Et2O ligand to yield the corresponding π complexes, [(IMes)3Fe4S4(PhCCH)][BArF4] and [(IMes)3Fe4S4(COE)][BArF4]. EPR spectroscopic analysis demonstrates that both clusters are doublets with giso > 2 and thus are spectroscopically faithful models of the analogous species characterized in the isoprenoid biosynthetic enzymes IspG and IspH. Structural and Mössbauer spectroscopic analysis reveals that both complexes are best described as [Fe4S4]+ clusters in which the unique Fe site engages in modest back-bonding to the π-acidic ligand. Paramagnetic NMR studies show that, even at room temperature, the alkyne/alkene-bound Fe centers harbor minority spin and therefore adopt an Fe2+ valence. We propose that such valence localization could likewise occur in Fe-S enzymes that interact with π-acidic molecules.
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10
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Scott AG, Agapie T. Synthesis of a Fe 3-Carbyne Motif by Oxidation of an Alkyl Ligated Iron-Sulfur (WFe 3S 3) Cluster. J Am Chem Soc 2023; 145:2-6. [PMID: 36537723 PMCID: PMC10575540 DOI: 10.1021/jacs.2c04826] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The presence of a carbide ligand in the active site of nitrogenases remains an unusual example of organometallic chemistry employed by a protein. Carbide incorporation into the MFe7S9C cluster involves complex biosynthesis, but analogous synthetic methodologies are limited. Herein, we present a new synthetic strategy for incorporating carbon based bridging ligands into iron-sulfur clusters. Starting from a halide precursor, a WFe3S3 cluster displaying three terminal alkyl ligands and an open Fe3 face was prepared. Oxidation results in loss of alkane and formation of a μ3-carbyne. Characterization of these clusters and mechanistic studies are presented.
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Affiliation(s)
- Anna G Scott
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Theodor Agapie
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
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11
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Kim Y, Sridharan A, Suess DLM. The Elusive Mononitrosylated [Fe 4 S 4 ] Cluster in Three Redox States. Angew Chem Int Ed Engl 2022; 61:e202213032. [PMID: 36194444 PMCID: PMC9669169 DOI: 10.1002/anie.202213032] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2022] [Indexed: 11/06/2022]
Abstract
Iron-sulfur clusters are well-established targets in biological nitric oxide (NO) chemistry, but the key intermediate in these processes-a mononitrosylated [Fe4 S4 ] cluster-has not been fully characterized in a protein or a synthetic model thereof. Here, we report the synthesis of a three-member redox series of isostructural mononitrosylated [Fe4 S4 ] clusters. Mononitrosylation was achieved by binding NO to a 3 : 1 site-differentiated [Fe4 S4 ]+ cluster; subsequent oxidation and reduction afforded the other members of the series. All three clusters feature a local high-spin Fe3+ center antiferromagnetically coupled to 3 [NO]- . The observation of an anionic NO ligand suggests that NO binding is accompanied by formal electron transfer from the cluster to NO. Preliminary reactivity studies with the monocationic cluster demonstrate that exposure to excess NO degrades the cluster, supporting the intermediacy of mononitrosylated intermediates in NO sensing/signaling.
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Affiliation(s)
- Youngsuk Kim
- Department of ChemistryMassachusetts Institute of Technology77 Massachusetts AveCambridgeMA 02139USA
- Department of ChemistryPusan National UniversityBusan46241Republic of Korea
| | - Arun Sridharan
- Department of ChemistryMassachusetts Institute of Technology77 Massachusetts AveCambridgeMA 02139USA
| | - Daniel L. M. Suess
- Department of ChemistryMassachusetts Institute of Technology77 Massachusetts AveCambridgeMA 02139USA
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12
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Ho MB, Jodts RJ, Kim Y, McSkimming A, Suess DLM, Hoffman BM. Characterization by ENDOR Spectroscopy of the Iron–Alkyl Bond in a Synthetic Counterpart of Organometallic Intermediates in Radical SAM Enzymes. J Am Chem Soc 2022; 144:17642-17650. [DOI: 10.1021/jacs.2c07155] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Madeline B. Ho
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - Richard J. Jodts
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - Youngsuk Kim
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Alex McSkimming
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Daniel L. M. Suess
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Brian M. Hoffman
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
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13
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Ye M, Brown AC, Suess DLM. Reversible Alkyl-Group Migration between Iron and Sulfur in [Fe 4S 4] Clusters. J Am Chem Soc 2022; 144:13184-13195. [PMID: 35830717 DOI: 10.1021/jacs.2c03195] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Synthetic [Fe4S4] clusters with Fe-R groups (R = alkyl/benzyl) are shown to release organic radicals on an [Fe4S4]3+-R/[Fe4S4]2+ redox couple, the same that has been proposed for a radical-generating intermediate in the superfamily of radical S-adenosyl-l-methionine (SAM) enzymes. In attempts to trap the immediate precursor to radical generation, a species in which the alkyl group has migrated from Fe to S is instead isolated. This S-alkylated cluster is a structurally faithful model of intermediates proposed in a variety of functionally diverse S transferase enzymes and features an "[Fe4S4]+-like" core that exists as a physical mixture of S = 1/2 and 7/2 states. The latter corresponds to an unusual, valence-localized electronic structure as indicated by distortions in its geometric structure and supported by computational analysis. Fe-to-S alkyl group migration is (electro)chemically reversible, and the preference for Fe vs S alkylation is dictated by the redox state of the cluster. These findings link the organoiron and organosulfur chemistry of Fe-S clusters and are discussed in the context of metalloenzymes that are proposed to make and break Fe-S and/or C-S bonds during catalysis.
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Affiliation(s)
- Mengshan Ye
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Alexandra C Brown
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Daniel L M Suess
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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14
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Jeyachandran VR, Boal AK. Structural insights into auxiliary cofactor usage by radical S-adenosylmethionine enzymes. Curr Opin Chem Biol 2022; 68:102153. [PMID: 35512465 DOI: 10.1016/j.cbpa.2022.102153] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2021] [Revised: 03/22/2022] [Accepted: 03/28/2022] [Indexed: 11/03/2022]
Abstract
Radical S-adenosylmethionine (SAM) enzymes use a common catalytic core for diverse transformations. While all radical SAM enzymes bind a Fe4S4 cluster via a characteristic tri-cysteine motif, many bind additional metal cofactors. Recently reported structures of radical SAM enzymes that use methylcobalamin or additional iron-sulfur clusters as cosubstrates show that these auxiliary units are anchored by N- and C-terminal domains that vary significantly in size and topology. Despite this architectural diversity, all use a common surface for auxiliary cofactor docking. In the sulfur insertion and metallocofactor assembly systems evaluated here, interaction with iron-sulfur cluster assembly proteins or downstream scaffold proteins is an important component of catalysis. Structures of these complexes represent important new frontiers in structural analysis of radical SAM enzymes.
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Affiliation(s)
- Vivian Robert Jeyachandran
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA, 16802, USA
| | - Amie K Boal
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA, 16802, USA; Department of Chemistry, The Pennsylvania State University, University Park, PA, 16802, USA.
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15
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Ulrich EC, Drennan CL. The Atypical Cobalamin-Dependent S-Adenosyl-l-Methionine Nonradical Methylase TsrM and Its Radical Counterparts. J Am Chem Soc 2022; 144:5673-5684. [PMID: 35344653 PMCID: PMC8992657 DOI: 10.1021/jacs.1c12064] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Cobalamin (Cbl)-dependent S-adenosyl-l-methionine (AdoMet) radical methylases are known for their use of a dual cofactor system to perform challenging radical methylation reactions at unactivated carbon and phosphorus centers. These enzymes are part of a larger subgroup of Cbl-dependent AdoMet radical enzymes that also perform difficult ring contractions and radical rearrangements. This subgroup is a largely untapped reservoir of diverse chemistry that requires steady efforts in biochemical and structural characterization to reveal its complexity. In this Perspective, we highlight the significant efforts over many years to elucidate the function, mechanism, and structure of TsrM, an unexpected nonradical methylase in this subgroup. We also discuss recent achievements in characterizing radical methylase subgroup members that exemplify how key tools in mechanistic enzymology are valuable time and again. Finally, we identify recent enzyme activity studies that have made use of bioinformatic analyses to expand our definition of the subgroup. Additional breakthroughs in radical (and nonradical) enzymatic chemistry and challenging transformations from the unexplored space of this subgroup are undoubtedly on the horizon.
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Affiliation(s)
| | - Catherine L Drennan
- Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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16
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Lundahl MN, Sarksian R, Yang H, Jodts RJ, Pagnier A, Smith DF, Mosquera MA, van der Donk WA, Hoffman BM, Broderick WE, Broderick JB. Mechanism of Radical S-Adenosyl-l-methionine Adenosylation: Radical Intermediates and the Catalytic Competence of the 5'-Deoxyadenosyl Radical. J Am Chem Soc 2022; 144:5087-5098. [PMID: 35258967 PMCID: PMC9524473 DOI: 10.1021/jacs.1c13706] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Radical S-adenosyl-l-methionine (SAM) enzymes employ a [4Fe-4S] cluster and SAM to initiate diverse radical reactions via either H-atom abstraction or substrate adenosylation. Here we use freeze-quench techniques together with electron paramagnetic resonance (EPR) spectroscopy to provide snapshots of the reaction pathway in an adenosylation reaction catalyzed by the radical SAM enzyme pyruvate formate-lyase activating enzyme on a peptide substrate containing a dehydroalanine residue in place of the target glycine. The reaction proceeds via the initial formation of the organometallic intermediate Ω, as evidenced by the characteristic EPR signal with g∥ = 2.035 and g⊥ = 2.004 observed when the reaction is freeze-quenched at 500 ms. Thermal annealing of frozen Ω converts it into a second paramagnetic species centered at giso = 2.004; this second species was generated directly using freeze-quench at intermediate times (∼8 s) and unequivocally identified via isotopic labeling and EPR spectroscopy as the tertiary peptide radical resulting from adenosylation of the peptide substrate. An additional paramagnetic species observed in samples quenched at intermediate times was revealed through thermal annealing while frozen and spectral subtraction as the SAM-derived 5'-deoxyadenosyl radical (5'-dAdo•). The time course of the 5'-dAdo• and tertiary peptide radical EPR signals reveals that the former generates the latter. These results thus support a mechanism in which Ω liberates 5'-dAdo• by Fe-C5' bond homolysis, and the 5'-dAdo• attacks the dehydroalanine residue of the peptide substrate to form the adenosylated peptide radical species. The results thus provide a picture of a catalytically competent 5'-dAdo• intermediate trapped just prior to reaction with the substrate.
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Affiliation(s)
- Maike N. Lundahl
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States
| | - Raymond Sarksian
- Department of Chemistry and Howard Hughes Medical Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Hao Yang
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - Richard J. Jodts
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - Adrien Pagnier
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States
| | - Donald F. Smith
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States
| | - Martín A. Mosquera
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States
| | - Wilfred A. van der Donk
- Department of Chemistry and Howard Hughes Medical Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Brian M. Hoffman
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - William E. Broderick
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States
| | - Joan B. Broderick
- Corresponding Author: Joan B. Broderick – Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States;
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17
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Donnan PH, Mansoorabadi SO. Broken-Symmetry Density Functional Theory Analysis of the Ω Intermediate in Radical S-Adenosyl-l-methionine Enzymes: Evidence for a Near-Attack Conformer over an Organometallic Species. J Am Chem Soc 2022; 144:3381-3385. [PMID: 35170316 DOI: 10.1021/jacs.2c00678] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Radical S-adenosyl-l-methionine (SAM) enzymes are found in all domains of life and catalyze a wide range of biochemical reactions. Recently, an organometallic intermediate, Ω, has been experimentally implicated in the 5'-deoxyadenosyl radical generation mechanism of the radical SAM superfamily. In this work, we employ broken-symmetry density functional theory to evaluate several structural models of Ω. The results show that the calculated hyperfine coupling constants (HFCCs) for the proposed organometallic structure of Ω are inconsistent with the experiment. In contrast, a near-attack conformer of SAM bound to the catalytic [4Fe-4S] cluster, in which the distance between the unique iron and SAM sulfur is ∼3 Å, yields HFCCs that are all within 1 MHz of the experimental values. These results clarify the structure of the ubiquitous Ω intermediate and suggest a paradigm shift reversal regarding the mechanism of SAM cleavage by members of the radical SAM superfamily.
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Affiliation(s)
- Patrick H Donnan
- Department of Chemistry and Biochemistry, Auburn University, 179 Chemistry Building, Auburn, Alabama 36849, United States
| | - Steven O Mansoorabadi
- Department of Chemistry and Biochemistry, Auburn University, 179 Chemistry Building, Auburn, Alabama 36849, United States
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18
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Zhou S, Wei WJ, Liao RZ. QM/MM Study of the Mechanism of the Noncanonical S-Cγ Bond Scission in S-Adenosylmethionine Catalyzed by the CmnDph2 Radical Enzyme. Top Catal 2022. [DOI: 10.1007/s11244-021-01420-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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19
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Feng J, Shaik S, Wang B. Spin‐Regulated Electron Transfer and Exchange‐Enhanced Reactivity in Fe
4
S
4
‐Mediated Redox Reaction of the Dph2 Enzyme During the Biosynthesis of Diphthamide. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202107008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Jianqiang Feng
- State Key Laboratory of Physical Chemistry of Solid Surfaces and Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry College of Chemistry and Chemical Engineering Xiamen University Xiamen 361005 China
| | - Sason Shaik
- Institute of Chemistry The Hebrew University of Jerusalem Jerusalem 9190401 Israel
| | - Binju Wang
- State Key Laboratory of Physical Chemistry of Solid Surfaces and Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry College of Chemistry and Chemical Engineering Xiamen University Xiamen 361005 China
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20
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Feng J, Shaik S, Wang B. Spin-Regulated Electron Transfer and Exchange-Enhanced Reactivity in Fe 4 S 4 -Mediated Redox Reaction of the Dph2 Enzyme During the Biosynthesis of Diphthamide. Angew Chem Int Ed Engl 2021; 60:20430-20436. [PMID: 34302311 DOI: 10.1002/anie.202107008] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2021] [Indexed: 11/06/2022]
Abstract
The [4Fe-4S]-dependent radical S-adenosylmethionine (SAM) proteins is one of large families of redox enzymes that are able to carry a panoply of challenging transformations. Despite the extensive studies of structure-function relationships of radical SAM (RS) enzymes, the electronic state-dependent reactivity of the [4Fe-4S] cluster in these enzymes remains elusive. Using combined MD simulations and QM/MM calculations, we deciphered the electronic state-dependent reactivity of the [4Fe-4S] cluster in Dph2, a key enzyme involved in the biosynthesis of diphthamide. Our calculations show that the reductive cleavage of the S-C(γ) bond is highly dependent on the electronic structure of [4Fe-4S]. Interestingly, the six electronic states can be classified into a low-energy and a high-energy groups, which are correlated with the net spin of Fe4 atom ligated to SAM. Due to the driving force of Fe4-C(γ) bonding, the net spin on the Fe4 moiety dictate the shift of the opposite spin electron from the Fe1-Fe2-Fe3 block to SAM. Such spin-regulated electron transfer results in the exchange-enhanced reactivity in the lower-energy group compared with those in the higher-energy group. This reactivity principle provides fundamental mechanistic insights into reactivities of [4Fe-4S] cluster in RS enzymes.
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Affiliation(s)
- Jianqiang Feng
- State Key Laboratory of Physical Chemistry of Solid Surfaces and Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005, China
| | - Sason Shaik
- Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem, 9190401, Israel
| | - Binju Wang
- State Key Laboratory of Physical Chemistry of Solid Surfaces and Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005, China
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21
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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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22
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Sridharan A, Brown AC, Suess DLM. A Terminal Imido Complex of an Iron-Sulfur Cluster. Angew Chem Int Ed Engl 2021; 60:12802-12806. [PMID: 33772994 DOI: 10.1002/anie.202102603] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2021] [Indexed: 11/10/2022]
Abstract
We report the synthesis and characterization of the first terminal imido complex of an Fe-S cluster, (IMes)3 Fe4 S4 =NDipp (2; IMes=1,3-dimesitylimidazol-2-ylidene, Dipp=2,6-diisopropylphenyl), which is generated by oxidative group transfer from DippN3 to the all-ferrous cluster (IMes)3 Fe4 S4 (PPh3 ). This two-electron process is achieved by formal one-electron oxidation of the imido-bound Fe site and one-electron oxidation of two IMes-bound Fe sites. Structural, spectroscopic, and computational studies establish that the Fe-imido site is best described as a high-spin Fe3+ center, which is manifested in its long Fe-N(imido) distance of 1.763(2) Å. Cluster 2 abstracts hydrogen atoms from 1,4-cyclohexadiene to yield the corresponding anilido complex, demonstrating competency for C-H activation.
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Affiliation(s)
- Arun Sridharan
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA, 02139, USA
| | - Alexandra C Brown
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA, 02139, USA
| | - Daniel L M Suess
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA, 02139, USA
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23
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Sridharan A, Brown AC, Suess DLM. A Terminal Imido Complex of an Iron–Sulfur Cluster. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202102603] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Arun Sridharan
- Department of Chemistry Massachusetts Institute of Technology 77 Massachusetts Ave Cambridge MA 02139 USA
| | - Alexandra C. Brown
- Department of Chemistry Massachusetts Institute of Technology 77 Massachusetts Ave Cambridge MA 02139 USA
| | - Daniel L. M. Suess
- Department of Chemistry Massachusetts Institute of Technology 77 Massachusetts Ave Cambridge MA 02139 USA
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24
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Speelman AL, Skubi KL, Mercado BQ, Holland PL. Synthesis and Reactivity of Iron Complexes with a Biomimetic SCS Pincer Ligand. Inorg Chem 2021; 60:1965-1974. [PMID: 33443404 DOI: 10.1021/acs.inorgchem.0c03427] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Recent experimental evidence suggests that the FeMoco of nitrogenase undergoes structural rearrangement during N2 reduction, which may result in the generation of coordinatively unsaturated iron sites with two sulfur donors and a carbon donor. In an effort to synthesize and study small-molecule model complexes with a one-carbon/two-sulfur coordination environment, we have designed two new SCS pincer ligands containing a central NHC donor accompanied by thioether- or thiolate-functionalized aryl groups. Metalation of the thioether ligand with Fe(OTf)2 gives 6-coordinate complexes in which the SCS ligand binds meridionally. In contrast, metalation of the thiolate ligand with Fe(HMDS)2 gives a four-coordinate pseudotetrahedral amide complex in which the ligand binds facially, illustrating the potential structural flexibility of these ligands. Reaction of the amide complex with a bulky monothiol gives a four-coordinate complex with a one-carbon/three-sulfur coordination environment that resembles the resting state of nitrogenase. Reaction of the amide complex with phenylhydrazine gives a product with a rare κ1-bound phenylhydrazido group which undergoes N-N cleavage to give a phenylamido complex.
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Affiliation(s)
- Amy L Speelman
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
| | - Kazimer L Skubi
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
| | - 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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25
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Construction of Synthetic Models for Nitrogenase-Relevant NifB Biogenesis Intermediates and Iron-Carbide-Sulfide Clusters. Catalysts 2020. [DOI: 10.3390/catal10111317] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
The family of nitrogenase enzymes catalyzes the reduction of atmospheric dinitrogen (N2) to ammonia under remarkably benign conditions of temperature, pressure, and pH. Therefore, the development of synthetic complexes or materials that can similarly perform this reaction is of critical interest. The primary obstacle for obtaining realistic synthetic models of the active site iron-sulfur-carbide cluster (e.g., FeMoco) is the incorporation of a truly inorganic carbide. This review summarizes the present state of knowledge regarding biological and chemical (synthetic) incorporation of carbide into iron-sulfur clusters. This includes the Nif cluster of proteins and associated biochemistry involved in the endogenous biogenesis of FeMoco. We focus on the chemical (synthetic) incorporation portion of our own efforts to incorporate and modify C1 units in iron/sulfur clusters. We also highlight recent contributions from other research groups in the area toward C1 and/or inorganic carbide insertion.
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26
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Pagnier A, Yang H, Jodts RJ, James CD, Shepard EM, Impano S, Broderick WE, Hoffman BM, Broderick JB. Radical SAM Enzyme Spore Photoproduct Lyase: Properties of the Ω Organometallic Intermediate and Identification of Stable Protein Radicals Formed during Substrate-Free Turnover. J Am Chem Soc 2020; 142:18652-18660. [PMID: 32966073 DOI: 10.1021/jacs.0c08585] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Spore photoproduct lyase is a radical S-adenosyl-l-methionine (SAM) enzyme with the unusual property that addition of SAM to the [4Fe-4S]1+ enzyme absent substrate results in rapid electron transfer to SAM with accompanying homolytic S-C5' bond cleavage. Herein, we demonstrate that this unusual reaction forms the organometallic intermediate Ω in which the unique Fe atom of the [4Fe-4S] cluster is bound to C5' of the 5'-deoxyadenosyl radical (5'-dAdo•). During catalysis, homolytic cleavage of the Fe-C5' bond liberates 5'-dAdo• for reaction with substrate, but here, we use Ω formation without substrate to determine the thermal stability of Ω. The reaction of Geobacillus thermodenitrificans SPL (GtSPL) with SAM forms Ω within ∼15 ms after mixing. By monitoring the decay of Ω through rapid freeze-quench trapping at progressively longer times we find an ambient temperature decay time of the Ω Fe-C5' bond of τ ≈ 5-6 s, likely shortened by enzymatic activation as is the case with the Co-C5' bond of B12. We have further used hand quenching at times up to 10 min, and thus with multiple SAM turnovers, to probe the fate of the 5'-dAdo• radical liberated by Ω. In the absence of substrate, Ω undergoes low-probability conversion to a stable protein radical. The WT enzyme with valine at residue 172 accumulates a Val•; mutation of Val172 to isoleucine or cysteine results in accumulation of an Ile• or Cys• radical, respectively. The structures of the radical in WT, V172I, and V172C variants have been established by detailed EPR/DFT analyses.
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Affiliation(s)
- Adrien Pagnier
- Department of Chemistry & Biochemistry, Montana State University, Bozeman, Montana. 59717, United States
| | - Hao Yang
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - Richard J Jodts
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - Christopher D James
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - Eric M Shepard
- Department of Chemistry & Biochemistry, Montana State University, Bozeman, Montana. 59717, United States
| | - Stella Impano
- Department of Chemistry & Biochemistry, Montana State University, Bozeman, Montana. 59717, United States
| | - William E Broderick
- Department of Chemistry & Biochemistry, Montana State University, Bozeman, Montana. 59717, United States
| | - Brian M Hoffman
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - Joan B Broderick
- Department of Chemistry & Biochemistry, Montana State University, Bozeman, Montana. 59717, United States
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