1
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Pierce BS, Schmittou AN, York NJ, Madigan RP, Nino PF, Foss FW, Lockart MM. Improved resolution of 3-mercaptopropionate dioxygenase active site provided by ENDOR spectroscopy offers insight into catalytic mechanism. J Biol Chem 2024; 300:105777. [PMID: 38395308 PMCID: PMC10966181 DOI: 10.1016/j.jbc.2024.105777] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2023] [Revised: 02/13/2024] [Accepted: 02/15/2024] [Indexed: 02/25/2024] Open
Abstract
3-mercaptopropionate (3MPA) dioxygenase (MDO) is a mononuclear nonheme iron enzyme that catalyzes the O2-dependent oxidation of thiol-bearing substrates to yield the corresponding sulfinic acid. MDO is a member of the cysteine dioxygenase family of small molecule thiol dioxygenases and thus shares a conserved sequence of active site residues (Serine-155, Histidine-157, and Tyrosine-159), collectively referred to as the SHY-motif. It has been demonstrated that these amino acids directly interact with the mononuclear Fe-site, influencing steady-state catalysis, catalytic efficiency, O2-binding, and substrate coordination. However, the underlying mechanism by which this is accomplished is poorly understood. Here, pulsed electron paramagnetic resonance spectroscopy [1H Mims electron nuclear double resonance spectroscopy] is applied to validate density functional theory computational models for the MDO Fe-site simultaneously coordinated by substrate and nitric oxide (NO), (3MPA/NO)-MDO. The enhanced resolution provided by electron nuclear double resonance spectroscopy allows for direct observation of Fe-bound substrate conformations and H-bond donation from Tyr159 to the Fe-bound NO ligand. Further inclusion of SHY-motif residues within the validated model reveals a distinct channel restricting movement of the Fe-bound NO-ligand. It has been argued that the iron-nitrosyl emulates the structure of potential Fe(III)-superoxide intermediates within the MDO catalytic cycle. While the merit of this assumption remains unconfirmed, the model reported here offers a framework to evaluate oxygen binding at the substrate-bound Fe-site and possible reaction mechanisms. It also underscores the significance of hydrogen bonding interactions within the enzymatic active site.
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Affiliation(s)
- Brad S Pierce
- Department of Chemistry & Biochemistry, University of Alabama, Tuscaloosa, Alabama, USA.
| | - Allison N Schmittou
- Department of Chemistry & Biochemistry, University of Alabama, Tuscaloosa, Alabama, USA
| | - Nicholas J York
- Department of Chemistry & Biochemistry, University of Alabama, Tuscaloosa, Alabama, USA
| | - Ryan P Madigan
- Department of Chemistry & Biochemistry, The University of Texas at Arlington, Arlington, Texas, USA
| | - Paula F Nino
- Department of Chemistry & Biochemistry, The University of Texas at Arlington, Arlington, Texas, USA
| | - Frank W Foss
- Department of Chemistry & Biochemistry, The University of Texas at Arlington, Arlington, Texas, USA
| | - Molly M Lockart
- Department of Chemistry and Biochemistry, Samford University, Homewood, Alabama, USA.
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2
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Oloyede UN, Flowers RA. Coordination-induced bond weakening and small molecule activation by low-valent titanium complexes. Dalton Trans 2024; 53:2413-2441. [PMID: 38224159 DOI: 10.1039/d3dt03454b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2024]
Abstract
Bond activation of small molecules through coordination to low valent metal complexes in M⋯X-H type interactions (where X = O, N, B, Si, etc.) leads to the formation of unusually weak X-H bonds and provides a powerful approach for the synthesis of target compounds under very mild conditions. Coordination of small molecules like water, amides, silanes, boranes, and dinitrogen to Ti(III) or Ti(II) complexes results in the synergetic redistribution of electrons between the metal orbitals and the ligand orbitals which weakens and enables the facile cleavage of the X-H or N-N bonds of the ligands. This review presents an overview of coordination-induced bond activation of small molecules by low valent titanium complexes. In particular, the applications of low valent titanium-induced bond weakening in nitrogen fixation are presented. The review concludes with potential future directions for work in this area including low-valent Ti-based PCET systems, photocatalytic nitrogen reduction, and approaches to tailoring complexes for optimal bond activation.
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Affiliation(s)
| | - Robert A Flowers
- Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania 18015, USA.
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3
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Zars E, Gravogl L, Gau MR, Carroll PJ, Meyer K, Mindiola DJ. Isostructural bridging diferrous chalcogenide cores [Fe II(μ-E)Fe II] (E = O, S, Se, Te) with decreasing antiferromagnetic coupling down the chalcogenide series. Chem Sci 2023; 14:6770-6779. [PMID: 37350823 PMCID: PMC10283490 DOI: 10.1039/d3sc01094e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2023] [Accepted: 05/24/2023] [Indexed: 06/24/2023] Open
Abstract
Iron compounds containing a bridging oxo or sulfido moiety are ubiquitous in biological systems, but substitution with the heavier chalcogenides selenium and tellurium, however, is much rarer, with only a few examples reported to date. Here we show that treatment of the ferrous starting material [(tBupyrpyrr2)Fe(OEt2)] (1-OEt2) (tBupyrpyrr2 = 3,5-tBu2-bis(pyrrolyl)pyridine) with phosphine chalcogenide reagents E = PR3 results in the neutral phosphine chalcogenide adduct series [(tBupyrpyrr2)Fe(EPR3)] (E = O, S, Se; R = Ph; E = Te; R = tBu) (1-E) without any electron transfer, whereas treatment of the anionic starting material [K]2[(tBupyrpyrr2)Fe2(μ-N2)] (2-N2) with the appropriate chalcogenide transfer source yields cleanly the isostructural ferrous bridging mono-chalcogenide ate complexes [K]2[(tBupyrpyrr2)Fe2(μ-E)] (2-E) (E = O, S, Se, and Te) having significant deviation in the Fe-E-Fe bridge from linear in the case of E = O to more acute for the heaviest chalcogenide. All bridging chalcogenide complexes were analyzed using a variety of spectroscopic techniques, including 1H NMR, UV-Vis electronic absorbtion, and 57Fe Mössbauer. The spin-state and degree of communication between the two ferrous ions were probed via SQUID magnetometry, where it was found that all iron centers were high-spin (S = 2) FeII, with magnetic exchange coupling between the FeII ions. Magnetic studies established that antiferromagnetic coupling between the ferrous ions decreases as the identity of the chalcogen is tuned from O to the heaviest congener Te.
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Affiliation(s)
- Ethan Zars
- Department of Chemistry, University of Pennsylvania 231 S 34th St Philadelphia PA 19104 USA
| | - Lisa Gravogl
- Department of Chemistry & Pharmacy, Friedrich-Alexander-Universität Erlangen - Nürnberg (FAU) Egerlandstr. 1 91058 Erlangen Bavaria Germany
| | - Michael R Gau
- Department of Chemistry, University of Pennsylvania 231 S 34th St Philadelphia PA 19104 USA
| | - Patrick J Carroll
- Department of Chemistry, University of Pennsylvania 231 S 34th St Philadelphia PA 19104 USA
| | - Karsten Meyer
- Department of Chemistry & Pharmacy, Friedrich-Alexander-Universität Erlangen - Nürnberg (FAU) Egerlandstr. 1 91058 Erlangen Bavaria Germany
| | - Daniel J Mindiola
- Department of Chemistry, University of Pennsylvania 231 S 34th St Philadelphia PA 19104 USA
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4
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Boekell NG, Bartulovich CO, Maity S, Flowers RA. Accessing Unusual Reactivity through Chelation-Promoted Bond Weakening. Inorg Chem 2023; 62:5040-5045. [PMID: 36912617 DOI: 10.1021/acs.inorgchem.3c00298] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/14/2023]
Abstract
Highly reducing Sm(II) reductants and protic ligands were used as a platform to ascertain the relationship between low-valent metal-protic ligand affinity and degree of ligand X-H bond weakening with the goal of forming potent proton-coupled electron transfer (PCET) reductants. Among the Sm(II)-protic ligand reductant systems investigated, the samarium dibromide N-methylethanolamine (SmBr2-NMEA) reagent system displayed the best combination of metal-ligand affinity and stability against H2 evolution. The use of SmBr2-NMEA afforded the reduction of a range of substrates that are typically recalcitrant to single-electron reduction including alkynes, lactones, and arenes as stable as biphenyl. Moreover, the unique role of NMEA as a chelating ligand for Sm(II) was demonstrated by the reductive cyclization of unactivated esters bearing pendant olefins in contrast to the SmBr2-water-amine system. Finally, the SmBr2-NMEA reagent system was found to reduce substrates analogous to key intermediates in the nitrogen fixation process. These results reveal SmBr2-NMEA to be a powerful reductant for a wide range of challenging substrates and demonstrate the potential for the rational design of PCET reagents with exceptionally weak X-H bonds.
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Affiliation(s)
- Nicholas G Boekell
- Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania 18015, United States
| | - Caroline O Bartulovich
- Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania 18015, United States
| | - Sandeepan Maity
- Department of Chemistry, C. V. Raman Global University, Bhubaneswar, Odisha 752054, India
| | - Robert A Flowers
- Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania 18015, United States
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5
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Abstract
Coordination-induced bond weakening is a phenomenon wherein ligand X-H bond homolysis occurs in concert with the energetically favorable oxidation of a coordinating metal complex. The coupling of these two processes enables thermodynamically favorable proton-coupled electron transfer reductions to form weak bonds upon formal hydrogen atom transfer to substrates. Moreover, systems utilizing coordination-induced bond weakening have been shown to facilitate the dehydrogenation of feedstock molecules including water, ammonia, and primary alcohols under mild conditions. The formation of exceptionally weak substrate X-H bonds via small molecule homolysis is a powerful strategy in synthesis and has been shown to enable nitrogen fixation under mild conditions. Coordination-induced bond weakening has also been identified as an integral process in biophotosynthesis and has promising applications in renewable chemical fuel storage systems. This review presents a discussion of the advances made in the study of coordination-induced bond weakening to date. Because of the broad range of metal and ligand species implicated in coordination-induced bond weakening, each literature report is discussed individually and ordered by the identity of the low-valent metal. We then offer mechanistic insights into the basis of coordination-induced bond weakening and conclude with a discussion of opportunities for further research into the development and applications of coordination-induced bond weakening systems.
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Affiliation(s)
- Nicholas G Boekell
- Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania 18015, United States
| | - Robert A Flowers
- Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania 18015, United States
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6
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Ramírez-Solís A, Boekell NG, León-Pimentel CI, Saint-Martin H, Bartulovich CO, Flowers RA. Ammonia Solvation vs Aqueous Solvation of Samarium Diiodide. A Theoretical and Experimental Approach to Understanding Bond Activation Upon Coordination to Sm(II). J Org Chem 2021; 87:1689-1697. [PMID: 34775764 DOI: 10.1021/acs.joc.1c01771] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Coordination-induced desolvation or ligand displacement by cosolvents and additives is a key feature responsible for the reactivity of Sm(II)-based reagent systems. High-affinity proton donor cosolvents such as water and glycols also demonstrate coordination-induced bond weakening of the O-H bond, facilitating reduction of a broad range of substrates. In the present work, the coordination of ammonia to SmI2 was examined using Born-Oppenheimer molecular dynamics simulations and mechanistic studies, and the SmI2-ammonia system is compared to the SmI2-water system. The coordination number and reactivity of the SmI2-ammonia solvent system were found to be similar to those of SmI2-water but exhibited an order of magnitude greater rate of arene reduction by SmI2-ammonia than by SmI2-water at the same concentrations of cosolvent. In addition, upon coordination of ammonia to SmI2, the Sm(II)-ammonia solvate demonstrates one of the largest degrees of N-H bond weakening reported in the literature compared to known low-valent transition metal ammonia complexes.
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Affiliation(s)
- Alejandro Ramírez-Solís
- Depto. de Física, Centro de Investigación en Ciencias-IICBA, Universidad Autónoma del Estado de Morelos, Cuernavaca, Morelos 62209, México
| | - Nicholas G Boekell
- Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania 18015, United States
| | | | | | - Caroline O Bartulovich
- Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania 18015, United States
| | - Robert A Flowers
- Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania 18015, United States
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7
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Dobbelaar E, Rauber C, Bonck T, Kelm H, Schmitz M, de Waal Malefijt ME, Klein JEMN, Krüger HJ. Combining Structural with Functional Model Properties in Iron Synthetic Analogue Complexes for the Active Site in Rabbit Lipoxygenase. J Am Chem Soc 2021; 143:13145-13155. [PMID: 34383499 DOI: 10.1021/jacs.1c04422] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Iron complexes that model the structural and functional properties of the active iron site in rabbit lipoxygenase are described. The ligand sphere of the mononuclear pseudo-octahedral cis-(carboxylato)(hydroxo)iron(III) complex, which is completed by a tetraazamacrocyclic ligand, reproduces the first coordination shell of the active site in the enzyme. In addition, two corresponding iron(II) complexes are presented that differ in the coordination of a water molecule. In their structural and electronic properties, both the (hydroxo)iron(III) and the (aqua)iron(II) complex reflect well the only two essential states found in the enzymatic mechanism of peroxidation of polyunsaturated fatty acids. Furthermore, the ferric complex is shown to undergo hydrogen atom abstraction reactions with O-H and C-H bonds of suitable substrates, and the bond dissociation free energy of the coordinated water ligand of the ferrous complex is determined to be 72.4 kcal·mol-1. Theoretical investigations of the reactivity support a concerted proton-coupled electron transfer mechanism in close analogy to the initial step in the enzymatic mechanism. The propensity of the (hydroxo)iron(III) complex to undergo H atom abstraction reactions is the basis for its catalytic function in the aerobic peroxidation of 2,4,6-tri(tert-butyl)phenol and its role as a radical initiator in the reaction of dihydroanthracene with oxygen.
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Affiliation(s)
- Emiel Dobbelaar
- Department of Chemistry, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany
| | - Christian Rauber
- Department of Chemistry, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany
| | - Thorsten Bonck
- Department of Chemistry, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany
| | - Harald Kelm
- Department of Chemistry, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany
| | - Markus Schmitz
- Department of Chemistry, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany
| | - Matina Eloïse de Waal Malefijt
- Molecular Inorganic Chemistry, Stratingh Institute for Chemistry, Faculty of Science and Engineering, University of Groningen, Nijenborgh 9, 9747 AG Groningen, The Netherlands
| | - Johannes E M N Klein
- Molecular Inorganic Chemistry, Stratingh Institute for Chemistry, Faculty of Science and Engineering, University of Groningen, Nijenborgh 9, 9747 AG Groningen, The Netherlands
| | - Hans-Jörg Krüger
- Department of Chemistry, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany
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8
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York NJ, Lockart MM, Sardar S, Khadka N, Shi W, Stenkamp RE, Zhang J, Kiser PD, Pierce BS. Structure of 3-mercaptopropionic acid dioxygenase with a substrate analog reveals bidentate substrate binding at the iron center. J Biol Chem 2021; 296:100492. [PMID: 33662397 PMCID: PMC8050391 DOI: 10.1016/j.jbc.2021.100492] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2021] [Revised: 02/18/2021] [Accepted: 02/26/2021] [Indexed: 12/20/2022] Open
Abstract
Thiol dioxygenases are a subset of nonheme iron oxygenases that catalyze the formation of sulfinic acids from sulfhydryl-containing substrates and dioxygen. Among this class, cysteine dioxygenases (CDOs) and 3-mercaptopropionic acid dioxygenases (3MDOs) are the best characterized, and the mode of substrate binding for CDOs is well understood. However, the manner in which 3-mercaptopropionic acid (3MPA) coordinates to the nonheme iron site in 3MDO remains a matter of debate. A model for bidentate 3MPA coordination at the 3MDO Fe-site has been proposed on the basis of computational docking, whereas steady-state kinetics and EPR spectroscopic measurements suggest a thiolate-only coordination of the substrate. To address this gap in knowledge, we determined the structure of Azobacter vinelandii 3MDO (Av3MDO) in complex with the substrate analog and competitive inhibitor, 3-hydroxypropionic acid (3HPA). The structure together with DFT computational modeling demonstrates that 3HPA and 3MPA associate with iron as chelate complexes with the substrate-carboxylate group forming an additional interaction with Arg168 and the thiol bound at the same position as in CDO. A chloride ligand was bound to iron in the coordination site assigned as the O2-binding site. Supporting HYSCORE spectroscopic experiments were performed on the (3MPA/NO)-bound Av3MDO iron nitrosyl (S = 3/2) site. In combination with spectroscopic simulations and optimized DFT models, this work provides an experimentally verified model of the Av3MDO enzyme-substrate complex, effectively resolving a debate in the literature regarding the preferred substrate-binding denticity. These results elegantly explain the observed 3MDO substrate specificity, but leave unanswered questions regarding the mechanism of substrate-gated reactivity with dioxygen.
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Affiliation(s)
- Nicholas J York
- Department of Chemistry & Biochemistry, University of Alabama, Tuscaloosa, Alabama, USA
| | - Molly M Lockart
- Department of Chemistry & Biochemistry, University of Alabama, Tuscaloosa, Alabama, USA
| | - Sinjinee Sardar
- Department of Chemistry & Biochemistry, The University of Texas at Arlington, Arlington, Texas, USA
| | - Nimesh Khadka
- Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio, USA
| | - Wuxian Shi
- National Synchrotron Light Source-II, Brookhaven National Laboratory, Upton, New York, USA
| | - Ronald E Stenkamp
- Departments of Biological Structure and Biochemistry, University of Washington, Seattle, Washington, USA
| | - Jianye Zhang
- Department of Ophthalmology, School of Medicine, University of California, Irvine, Irvine, California, USA
| | - Philip D Kiser
- Department of Ophthalmology, School of Medicine, University of California, Irvine, Irvine, California, USA; Department of Physiology & Biophysics, School of Medicine, University of California, Irvine, Irvine, California, USA; Research Service, VA Long Beach Healthcare System, Long Beach, California, USA.
| | - Brad S Pierce
- Department of Chemistry & Biochemistry, University of Alabama, Tuscaloosa, Alabama, USA.
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9
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Ding CW, Luo W, Zhou JY, Ma XJ, Chen GH, Zhou XP, Li D. Hydroxo Iron(III) Sites in a Metal-Organic Framework: Proton-Coupled Electron Transfer and Catalytic Oxidation of Alcohol with Molecular Oxygen. ACS APPLIED MATERIALS & INTERFACES 2019; 11:45621-45628. [PMID: 31724842 DOI: 10.1021/acsami.9b15311] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Metalloenzymes are powerful biocatalysts that can catalyze particular chemical reactions with high activity, selectivity, and specificity under mild conditions. Metal-organic frameworks (MOFs) composed of metal ions or metal clusters and organic ligands with defined cavities have the potential to impart enzyme-like catalytic activity and mimic metalloenzymes. Here, a new metal-organic framework implanted with hydroxo iron(III) sites with the structural and reactivity characteristics of iron-containing lipoxygenases is reported. Similar to lipoxygenases, the hydrogen atoms and electrons of the substrate can transfer to the hydroxo iron(III) sites, showing typical proton-coupled electron transfer behavior. In the reactivity mimicking biology system, similar to alcohol oxidase, the material also catalyses the oxidation of alcohol into aldehyde by using O2 with a high yield and 100% selectivity under mild conditions, without the use of a radical cocatalyst or photoexcitation. These results provide strong evidence for the high structural fidelity of enzymatically active sites in MOF materials, verifying that MOFs provide an ideal platform for designing biomimetic heterogeneous catalysts with high conversion efficiency and product selectivity.
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Affiliation(s)
- Chong-Wei Ding
- College of Chemistry and Materials Science , Jinan University , Guangzhou , Guangdong 510632 , P. R. China
- Department of Chemistry , Shantou University , Shantou , Guangdong 515063 , P. R. China
| | - Wenzhi Luo
- Department of Chemistry , Shantou University , Shantou , Guangdong 515063 , P. R. China
| | - Jie-Yi Zhou
- College of Chemistry and Materials Science , Jinan University , Guangzhou , Guangdong 510632 , P. R. China
- Department of Chemistry , Shantou University , Shantou , Guangdong 515063 , P. R. China
| | - Xin-Jie Ma
- Department of Chemistry , Shantou University , Shantou , Guangdong 515063 , P. R. China
| | - Guang-Hui Chen
- Department of Chemistry , Shantou University , Shantou , Guangdong 515063 , P. R. China
| | - Xiao-Ping Zhou
- College of Chemistry and Materials Science , Jinan University , Guangzhou , Guangdong 510632 , P. R. China
| | - Dan Li
- College of Chemistry and Materials Science , Jinan University , Guangzhou , Guangdong 510632 , P. R. China
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10
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Narwane M, Chang YL, Ching WM, Tsai ML, Hsu SC. Investigation on the coordination behaviors of tris(2-pyridyl)pyrazolyl borates iron(II) complexes. Inorganica Chim Acta 2019. [DOI: 10.1016/j.ica.2019.118966] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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11
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Yadav V, Gordon JB, Siegler MA, Goldberg DP. Dioxygen-Derived Nonheme Mononuclear Fe III(OH) Complex and Its Reactivity with Carbon Radicals. J Am Chem Soc 2019; 141:10148-10153. [PMID: 31244183 DOI: 10.1021/jacs.9b03329] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
A new tetradentate, monoanionic, mixed N/O donor ligand (BNPAPh2O-) with second coordination sphere H-bonding groups has been synthesized for stabilization of a terminal FeIII(OH) complex. The complex FeII(BNPAPh2O)(OTf) (1) reacts with O2 to give a mononuclear terminal FeIII(OH) complex, FeIII(OH)(BNPAPh2O)(OTf) (2), both of which were characterized by X-ray diffraction, electrospray ionization mass spectrometry, UV-vis, 1H and 19F nuclear magnetic resonance, 57Fe Mössbauer, and electron paramagnetic resonance spectroscopies. Treatment of 2 with carbon radicals (Ar3C·) gives Ar3COH and the FeII complex 1, in direct analogy with the elusive radical "rebound" process proposed for nonheme iron enzymes.
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Affiliation(s)
- Vishal Yadav
- Department of Chemistry , The Johns Hopkins University , Baltimore , Maryland 21218 , United States
| | - Jesse B Gordon
- Department of Chemistry , The Johns Hopkins University , Baltimore , Maryland 21218 , United States
| | - Maxime A Siegler
- Department of Chemistry , The Johns Hopkins University , Baltimore , Maryland 21218 , United States
| | - David P Goldberg
- Department of Chemistry , The Johns Hopkins University , Baltimore , Maryland 21218 , United States
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12
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Liu Y, Lau TC. Activation of Metal Oxo and Nitrido Complexes by Lewis Acids. J Am Chem Soc 2019; 141:3755-3766. [DOI: 10.1021/jacs.8b13100] [Citation(s) in RCA: 51] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Affiliation(s)
- Yingying Liu
- Department of Chemistry and Institute of Molecular Functional Materials, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Hong Kong 999077, China
| | - Tai-Chu Lau
- Department of Chemistry and Institute of Molecular Functional Materials, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Hong Kong 999077, China
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13
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Resa S, Millán A, Fuentes N, Crovetto L, Luisa Marcos M, Lezama L, Choquesillo-Lazarte D, Blanco V, Campaña AG, Cárdenas DJ, Cuerva JM. O–H and (CO)N–H bond weakening by coordination to Fe(ii). Dalton Trans 2019; 48:2179-2189. [DOI: 10.1039/c8dt04689a] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Coordination of hydroxyl/amide groups to Fe(ii) diminishes BDFEs of O–H and (CO)N–H bonds down to 76.0 and 80.5 kcal mol−1 respectively.
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14
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Zaragoza JPT, Siegler MA, Goldberg DP. A Reactive Manganese(IV)-Hydroxide Complex: A Missing Intermediate in Hydrogen Atom Transfer by High-Valent Metal-Oxo Porphyrinoid Compounds. J Am Chem Soc 2018. [PMID: 29542921 DOI: 10.1021/jacs.8b00350] [Citation(s) in RCA: 44] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
High-valent metal-hydroxide species are invoked as critical intermediates in both catalytic, metal-mediated O2 activation (e.g., by Fe porphyrin in Cytochrome P450) and O2 production (e.g., by the Mn cluster in Photosystem II). However, well-characterized mononuclear MIV(OH) complexes remain a rarity. Herein we describe the synthesis of MnIV(OH)(ttppc) (3) (ttppc = tris(2,4,6-triphenylphenyl) corrole), which has been characterized by X-ray diffraction (XRD). The large steric encumbrance of the ttppc ligand allowed for isolation of 3. The complexes MnV(O)(ttppc) (4) and MnIII(H2O)(ttppc) (1·H2O) were also synthesized and structurally characterized, providing a series of Mn complexes related only by the transfer of hydrogen atoms. Both 3 and 4 abstract an H atom from the O-H bond of 2,4-di- tert-butylphenol (2,4-DTBP) to give a radical coupling product in good yield (3 = 90(2)%, 4 = 91(5)%). Complex 3 reacts with 2,4-DTBP with a rate constant of k2 = 2.73(12) × 104 M-1 s-1, which is ∼3 orders of magnitude larger than 4 ( k2 = 17.4(1) M-1 s-1). Reaction of 3 with a series of para-substituted 2,6-di- tert-butylphenol derivatives (4-X-2,6-DTBP; X = OMe, Me, tBu, H) gives rate constants in the range k2 = 510(10)-36(1.4) M-1 s-1 and led to Hammett and Marcus plot correlations. Together with kinetic isotope effect measurements, it is concluded that O-H cleavage occurs by a concerted H atom transfer (HAT) mechanism and that the MnIV(OH) complex is a much more powerful H atom abstractor than the higher-valent MnV(O) complex, or even some FeIV(O) complexes.
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Affiliation(s)
- Jan Paulo T Zaragoza
- Department of Chemistry , The Johns Hopkins University , 3400 North Charles Street , Baltimore , Maryland 21218 , United States
| | - Maxime A Siegler
- Department of Chemistry , The Johns Hopkins University , 3400 North Charles Street , Baltimore , Maryland 21218 , United States
| | - David P Goldberg
- Department of Chemistry , The Johns Hopkins University , 3400 North Charles Street , Baltimore , Maryland 21218 , United States
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15
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Affiliation(s)
- Paolo Pirovano
- School of Chemistry and CRANN/AMBER Nanoscience Institute; Trinity College Dublin; The University of Dublin; College Green 2 Dublin Ireland
| | - Aidan R. McDonald
- School of Chemistry and CRANN/AMBER Nanoscience Institute; Trinity College Dublin; The University of Dublin; College Green 2 Dublin Ireland
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Klein JEMN, Draksharapu A, Shokri A, Cramer CJ, Que L. On the Lewis Acidity of the Oxoiron(IV) Unit in a Tetramethylcyclam Complex. Chemistry 2017; 24:5373-5378. [PMID: 29205555 DOI: 10.1002/chem.201704977] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2017] [Indexed: 11/08/2022]
Abstract
The correlation between oxidation state and Lewis acidity is well established for hexaquairon complexes in the +II and +III oxidation state, in which the higher oxidation state leads to a lower pKa for the bound H2 O ligand. This article addresses the Lewis acidity of the oxoiron(IV) complex [FeIV (O)(TMC)(OH2 )]2+ (1-OH2 ; TMC=1,4,8,11-tetramethylcyclam) by determining the pKa of the H2 O ligand. We establish that 1-OH2 has a pKa of 6.9±0.5, a value that falls in between those found for [FeIII (OH2 )6 ]3+ and [FeII (OH2 )6 ]2+ . This intermediate value can be readily rationalized by the presence of the highly basic oxide ligand that mitigates the Lewis acidity of the iron(IV) center. Although the oxo ligand occupies only one position in 1-OH2 , anti to all four methyl groups that protrude from the same face of the nonplanar TMC ligand, its conjugate base 1-OH exists as a mixture of syn and anti tautomers, which are related by proton transfer between the oxo and the hydroxo ligands.
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Affiliation(s)
- Johannes E M N Klein
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, 207 Pleasant St. S.E., Minneapolis, Minnesota, 55455, USA.,Present Address: Molecular Inorganic Chemistry, Stratingh Institute for Chemistry, Faculty of Science and Engineering, University of Groningen, Nijenborgh 4, 9747, AG Groningen, The Netherlands
| | - Apparao Draksharapu
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, 207 Pleasant St. S.E., Minneapolis, Minnesota, 55455, USA
| | - Alireza Shokri
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, 207 Pleasant St. S.E., Minneapolis, Minnesota, 55455, USA
| | - Christopher J Cramer
- Department of Chemistry, Supercomputing Institute, and Chemical Theory Center, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota, 55455, USA
| | - Lawrence Que
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, 207 Pleasant St. S.E., Minneapolis, Minnesota, 55455, USA
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Gao H, Groves JT. Fast Hydrogen Atom Abstraction by a Hydroxo Iron(III) Porphyrazine. J Am Chem Soc 2017; 139:3938-3941. [PMID: 28245648 DOI: 10.1021/jacs.6b13091] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
A reactive hydroxoferric porphyrazine complex, [(PyPz)FeIII(OH) (OH2)]4+ (1, PyPz = tetramethyl-2,3-pyridino porphyrazine), has been prepared via one-electron oxidation of the corresponding ferrous species [(PyPz)FeII(OH2)2]4+ (2). Electrochemical analysis revealed a pH-dependent and remarkably high FeIII-OH/FeII-OH2 reduction potential of 680 mV vs Ag/AgCl at pH 5.2. Nernstian behavior from pH 2 to pH 8 indicates a one-proton, one-electron interconversion throughout that range. The O-H bond dissociation energy of the FeII-OH2 complex was estimated to be 84 kcal mol-1. Accordingly, 1 reacts rapidly with a panel of substrates via C-H hydrogen atom transfer (HAT), reducing 1 to [(PyPz)FeII(OH2)2]4+ (2). The second-order rate constant for the reaction of [(PyPz)FeIII(OH) (OH2)]4+ with xanthene was 2.22 × 103 M-1 s-1, 5-6 orders of magnitude faster than other reported FeIII-OH complexes and faster than many ferryl complexes.
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Affiliation(s)
- Hongxin Gao
- Department of Chemistry, Princeton University , Princeton, New Jersey 08544, United States
| | - John T Groves
- Department of Chemistry, Princeton University , Princeton, New Jersey 08544, United States
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Ma K, Cheng J, Zhang J, Li M, Liu F, Zhang X. Dependence of Co/Fe ratios in Co-Fe layered double hydroxides on the structure and capacitive properties. Electrochim Acta 2016. [DOI: 10.1016/j.electacta.2016.03.082] [Citation(s) in RCA: 71] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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