1
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Heppe N, Gallenkamp C, Paul S, Segura-Salas N, von Rhein N, Kaiser B, Jaegermann W, Jafari A, Sergueev I, Krewald V, Kramm UI. Substituent Effects in Iron Porphyrin Catalysts for the Hydrogen Evolution Reaction. Chemistry 2023; 29:e202202465. [PMID: 36301727 DOI: 10.1002/chem.202202465] [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: 08/08/2022] [Revised: 10/27/2022] [Accepted: 10/27/2022] [Indexed: 11/07/2022]
Abstract
For a future hydrogen economy, non-precious metal catalysts for the water splitting reactions are needed that can be implemented on a global scale. Metal-nitrogen-carbon (MNC) catalysts with active sites constituting a metal center with fourfold coordination of nitrogen (MN4 ) show promising performance, but an optimization rooted in structure-property relationships has been hampered by their low structural definition. Porphyrin model complexes are studied to transfer insights from well-defined molecules to MNC systems. This work combines experiment and theory to evaluate the influence of porphyrin substituents on the electronic and electrocatalytic properties of MN4 centers with respect to the hydrogen evolution reaction (HER) in aqueous electrolyte. We found that the choice of substituent affects their utilization on the carbon support and their electrocatalytic performance. We propose an HER mechanism for supported iron porphyrin complexes involving a [FeII (P⋅)]- radical anion intermediate, in which a porphinic nitrogen atom acts as an internal base. While this work focuses on the HER, the limited influence of a simultaneous interaction with the support and an aqueous electrolyte will likely be transferrable to other catalytic applications.
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Affiliation(s)
- Nils Heppe
- Catalysts and Electrocatalysts, Department of Chemistry, Eduard-Zintl-Insitute for Inorganic and Physical Chemistry, Technical University Darmstadt, Otto-Berndt-Str. 3, 64287, Darmstadt, Germany
| | - Charlotte Gallenkamp
- Catalysts and Electrocatalysts, Department of Chemistry, Eduard-Zintl-Insitute for Inorganic and Physical Chemistry, Technical University Darmstadt, Otto-Berndt-Str. 3, 64287, Darmstadt, Germany.,Department of Chemistry, Theoretical Chemistry, Technical University Darmstadt, Alarich-Weiss-Str. 4, 64287, Darmstadt, Germany
| | - Stephen Paul
- Catalysts and Electrocatalysts, Department of Chemistry, Eduard-Zintl-Insitute for Inorganic and Physical Chemistry, Technical University Darmstadt, Otto-Berndt-Str. 3, 64287, Darmstadt, Germany
| | - Nicole Segura-Salas
- Catalysts and Electrocatalysts, Department of Chemistry, Eduard-Zintl-Insitute for Inorganic and Physical Chemistry, Technical University Darmstadt, Otto-Berndt-Str. 3, 64287, Darmstadt, Germany
| | - Niklas von Rhein
- Department of Chemistry, Theoretical Chemistry, Technical University Darmstadt, Alarich-Weiss-Str. 4, 64287, Darmstadt, Germany
| | - Bernhard Kaiser
- Institute of Materials Science, Surface Science Division, Technical University Darmstadt, Otto-Berndt-Str. 3, 64287, Darmstadt, Germany
| | - Wolfram Jaegermann
- Institute of Materials Science, Surface Science Division, Technical University Darmstadt, Otto-Berndt-Str. 3, 64287, Darmstadt, Germany
| | - Atefeh Jafari
- Deutsches Elektronen-Synchrotron, Notkestraße 85, 22607, Hamburg, Germany
| | - Ilya Sergueev
- Deutsches Elektronen-Synchrotron, Notkestraße 85, 22607, Hamburg, Germany
| | - Vera Krewald
- Department of Chemistry, Theoretical Chemistry, Technical University Darmstadt, Alarich-Weiss-Str. 4, 64287, Darmstadt, Germany
| | - Ulrike I Kramm
- Catalysts and Electrocatalysts, Department of Chemistry, Eduard-Zintl-Insitute for Inorganic and Physical Chemistry, Technical University Darmstadt, Otto-Berndt-Str. 3, 64287, Darmstadt, Germany
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2
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Mizrahi A, Bhowmik S, Manna AK, Sinha W, Kumar A, Saphier M, Mahammed A, Patra M, Fridman N, Zilbermann I, Kronik L, Gross Z. Electronic Coupling and Electrocatalysis in Redox Active Fused Iron Corroles. Inorg Chem 2022; 61:20725-20733. [PMID: 36512733 PMCID: PMC9799712 DOI: 10.1021/acs.inorgchem.2c01389] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Conjugated arrays composed of corrole macrocycles are increasingly more common, but their chemistry still lags behind that of their porphyrin counterparts. Here, we report on the insertion of iron(III) into a β,β-fused corrole dimer and on the electronic effects that this redox active metal center has on the already rich coordination chemistry of [H3tpfc] COT, where COT = cyclo-octatetraene and tpfc = tris(pentafluorophenyl)corrole. Synthetic manipulations were performed for the isolation and full characterization of both the 5-coordinate [FeIIItpfc(py)]2COT and 6-coordinate [FeIIItpfc(py)2]2COT, with one and two axial pyridine ligands per metal, respectively. X-Ray crystallography reveals a dome-shaped structure for [FeIIItpfc(py)]2COT and a perfectly planar geometry which (surprisingly at first) is also characterized by shorter Fe-N (corrole) and Fe-N (pyridine) distances. Computational investigations clarify that the structural phenomena are due to a change in the iron(III) spin state from intermediate (S = 3/2) to low (S = 1/2), and that both the 5- and 6-coordinated complexes are enthalpically favored. Yet, in contrast to iron(III) porphyrins, the formation enthalpy for the coordination of the first pyridine to Fe(III) corrole is more negative than that of the second pyridine coordination. Possible interactions between the two corrole subunits and the chelated iron ions were examined by UV-Vis spectroscopy, electrochemical techniques, and density functional theory (DFT). The large differences in the electronic spectra of the dimer relative to the monomer are concluded to be due to a reduced electronic gap, owing to the extensive electron delocalization through the fusing bridge. A cathodic sweep for the dimer discloses two redox processes, separated by 230 mV. The DFT self-consistent charge density for the neutral and cationic states (1- and 2-electron oxidized) reveals that the holes are localized on the macrocycle. A different picture emerges from the reduction process, where both the electrochemistry and the calculated charge density point toward two consecutive electron transfers with similar energetics, indicative of very weak electron communication between the two redox active iron(III) sites. The binuclear complex was determined to be a much better catalyst for the electrochemical hydrogen evolution reaction (HER) than the analogous mononuclear corrole.
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Affiliation(s)
- Amir Mizrahi
- Chemistry
Department, Nuclear Research Centre Negev, Beer-Sheva84190, Israel,Schulich
Faculty of Chemistry, Technion Institute
of Technology, Haifa3200003, Israel
| | - Susovan Bhowmik
- Schulich
Faculty of Chemistry, Technion Institute
of Technology, Haifa3200003, Israel,Bankura
Sammilani College (W.B), Bankura722102, India
| | - Arun K. Manna
- Department
of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot76100, Israel
| | - Woormileela Sinha
- Schulich
Faculty of Chemistry, Technion Institute
of Technology, Haifa3200003, Israel,Department
of Chemistry, BITS PilaniK K Birla Goa Campus, NH17B, Zuarinagar, Goa403726, India
| | - Amit Kumar
- Schulich
Faculty of Chemistry, Technion Institute
of Technology, Haifa3200003, Israel
| | - Magal Saphier
- Chemistry
Department, Nuclear Research Centre Negev, Beer-Sheva84190, Israel
| | - Atif Mahammed
- Schulich
Faculty of Chemistry, Technion Institute
of Technology, Haifa3200003, Israel
| | | | - Natalia Fridman
- Schulich
Faculty of Chemistry, Technion Institute
of Technology, Haifa3200003, Israel
| | - Israel Zilbermann
- Chemistry
Department, Nuclear Research Centre Negev, Beer-Sheva84190, Israel,Chemistry
Department, Ben-Gurion University of the
Negev, Beer-Sheva84105, Israel,
| | - Leeor Kronik
- Department
of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot76100, Israel,
| | - Zeev Gross
- Schulich
Faculty of Chemistry, Technion Institute
of Technology, Haifa3200003, Israel,
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3
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Lehnert N, Kim E, Dong HT, Harland JB, Hunt AP, Manickas EC, Oakley KM, Pham J, Reed GC, Alfaro VS. The Biologically Relevant Coordination Chemistry of Iron and Nitric Oxide: Electronic Structure and Reactivity. Chem Rev 2021; 121:14682-14905. [PMID: 34902255 DOI: 10.1021/acs.chemrev.1c00253] [Citation(s) in RCA: 96] [Impact Index Per Article: 32.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Nitric oxide (NO) is an important signaling molecule that is involved in a wide range of physiological and pathological events in biology. Metal coordination chemistry, especially with iron, is at the heart of many biological transformations involving NO. A series of heme proteins, nitric oxide synthases (NOS), soluble guanylate cyclase (sGC), and nitrophorins, are responsible for the biosynthesis, sensing, and transport of NO. Alternatively, NO can be generated from nitrite by heme- and copper-containing nitrite reductases (NIRs). The NO-bearing small molecules such as nitrosothiols and dinitrosyl iron complexes (DNICs) can serve as an alternative vehicle for NO storage and transport. Once NO is formed, the rich reaction chemistry of NO leads to a wide variety of biological activities including reduction of NO by heme or non-heme iron-containing NO reductases and protein post-translational modifications by DNICs. Much of our understanding of the reactivity of metal sites in biology with NO and the mechanisms of these transformations has come from the elucidation of the geometric and electronic structures and chemical reactivity of synthetic model systems, in synergy with biochemical and biophysical studies on the relevant proteins themselves. This review focuses on recent advancements from studies on proteins and model complexes that not only have improved our understanding of the biological roles of NO but also have provided foundations for biomedical research and for bio-inspired catalyst design in energy science.
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Affiliation(s)
- Nicolai Lehnert
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Eunsuk Kim
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
| | - Hai T Dong
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Jill B Harland
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Andrew P Hunt
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Elizabeth C Manickas
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Kady M Oakley
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
| | - John Pham
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
| | - Garrett C Reed
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Victor Sosa Alfaro
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
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4
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Wu T, Brooksby PA, Fitchett CM, Downard AJ. Immobilisation of Iron Porphyrin from an Equilibrium Solution with Diazonium‐Functionalised Axial Ligand: Dependence of Film Composition on Grafting Potential. ChemElectroChem 2021. [DOI: 10.1002/celc.202100712] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Ting Wu
- School of Physical and Chemical Sciences University of Canterbury Christchurch 8140 New Zealand
| | - Paula A. Brooksby
- School of Physical and Chemical Sciences University of Canterbury Christchurch 8140 New Zealand
| | - Christopher M. Fitchett
- School of Physical and Chemical Sciences University of Canterbury Christchurch 8140 New Zealand
| | - Alison J. Downard
- School of Physical and Chemical Sciences University of Canterbury Christchurch 8140 New Zealand
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5
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Liberman I, Shimoni R, Ifraemov R, Rozenberg I, Singh C, Hod I. Active-Site Modulation in an Fe-Porphyrin-Based Metal-Organic Framework through Ligand Axial Coordination: Accelerating Electrocatalysis and Charge-Transport Kinetics. J Am Chem Soc 2020; 142:1933-1940. [PMID: 31910614 PMCID: PMC7467674 DOI: 10.1021/jacs.9b11355] [Citation(s) in RCA: 92] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
![]()
The construction of artificial solar
fuel generating systems requires
the heterogenization of large quantities of catalytically active sites
on electrodes. In that sense, metal–organic frameworks (MOFs)
have been utilized to assemble unpreceded concentration of electrochemically
active molecular catalysts to drive energy-conversion electrocatalytic
reactions. However, despite recent advances in MOF-based electrocatalysis,
so far no attempt has been made to exploit their unique chemical modularity
in order to tailor the electrocatalytic function of MOF-anchored active
sites at the molecular level. Here, we show that the axial coordination
of electron-donating ligands to active MOF-installed Fe-porphyrins
dramatically alters their electronic properties, accelerating the
rates of both redox-based MOF conductivity and the electrocatalytic
oxygen reduction reaction (ORR). Additionally, electrochemical characterizations
show that in multiple proton-coupled electron transfer reactions MOF-based
redox hopping is not the only factor that limits the overall electrocatalytic
rate. Hence, future efforts to enhance the efficiency of electrocatalytic
MOFs should also consider other important kinetic parameters such
as the rate of proton-associated chemical steps as well as mass-transport
rates of counterions, protons, and reactants toward catalytically
active sites.
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Affiliation(s)
- Itamar Liberman
- Department of Chemistry and Ilse Katz Institute for Nanoscale Science and Technology , Ben-Gurion University of the Negev , Beer-Sheva 8410501 , Israel
| | - Ran Shimoni
- Department of Chemistry and Ilse Katz Institute for Nanoscale Science and Technology , Ben-Gurion University of the Negev , Beer-Sheva 8410501 , Israel
| | - Raya Ifraemov
- Department of Chemistry and Ilse Katz Institute for Nanoscale Science and Technology , Ben-Gurion University of the Negev , Beer-Sheva 8410501 , Israel
| | - Illya Rozenberg
- Department of Chemistry and Ilse Katz Institute for Nanoscale Science and Technology , Ben-Gurion University of the Negev , Beer-Sheva 8410501 , Israel
| | - Chanderpratap Singh
- Department of Chemistry and Ilse Katz Institute for Nanoscale Science and Technology , Ben-Gurion University of the Negev , Beer-Sheva 8410501 , Israel
| | - Idan Hod
- Department of Chemistry and Ilse Katz Institute for Nanoscale Science and Technology , Ben-Gurion University of the Negev , Beer-Sheva 8410501 , Israel
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6
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Maindan K, Li X, Yu J, Deria P. Controlling Charge-Transport in Metal-Organic Frameworks: Contribution of Topological and Spin-State Variation on the Iron-Porphyrin Centered Redox Hopping Rate. J Phys Chem B 2019; 123:8814-8822. [PMID: 31535556 DOI: 10.1021/acs.jpcb.9b07506] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Metal-organic frameworks (MOFs) are an emerging class of compositions for electro- and photoelectrocatalytic energy conversion processes. Understanding and improving the charge-transport processes within these high surface area molecular redox catalyst assemblies are critical since the charge carrier conductivity is inherently limited in MOFs. Here, we examine a series of four chemically identical but structurally different hydrolytically robust ZrIV-MOFs constructed from tetrakis(4-carboxyphenyl)porphyrinato iron(III), TCPP(FeIII) to understand how their topological construction affects redox hopping conductivity. While a structural variation fixes center-to-center distances to define the hopping rate, we probe that altering the central metal spin-state can further tune the TCPP(FeIII/II) reorganization energy of the self-exchange process. Significant increase in the hopping rate was observed upon axial coordination of 1-methyl imidazole (MIM), which converts a weakly halide bound high-spin (HS) TCPP(FeIII/II) to the six-coordinated low-spin (LS) complex. Our electrochemical and resonance Raman data reveal that pore geometry that defines the Fe-Fe distance in these frameworks dictate the steric demand to accommodate two MIM-molecules, and thus, the population of LS vs HS species is a function of topology in the presence of an excess ligand.
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Affiliation(s)
- Karan Maindan
- Department of Chemistry and Biochemistry , Southern Illinois University , 1245 Lincoln Drive , Carbondale , Illinois 62901 , United States
| | - Xinlin Li
- Department of Chemistry and Biochemistry , Southern Illinois University , 1245 Lincoln Drive , Carbondale , Illinois 62901 , United States
| | - Jierui Yu
- Department of Chemistry and Biochemistry , Southern Illinois University , 1245 Lincoln Drive , Carbondale , Illinois 62901 , United States
| | - Pravas Deria
- Department of Chemistry and Biochemistry , Southern Illinois University , 1245 Lincoln Drive , Carbondale , Illinois 62901 , United States
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7
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New insights on the electronic, magnetic, electric and molecular structure of a bis-(4-cyanopyridine) iron(III) complex with the meso-tetrakis(4-methoxyphenyl)porphyrin. Inorganica Chim Acta 2019. [DOI: 10.1016/j.ica.2018.11.040] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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8
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Light-controlled switching of the spin state of iron(III). Nat Commun 2018; 9:4750. [PMID: 30420598 PMCID: PMC6232099 DOI: 10.1038/s41467-018-07023-1] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2018] [Accepted: 10/08/2018] [Indexed: 11/17/2022] Open
Abstract
Controlled switching of the spin state of transition metal ions, particularly of FeII and FeIII, is a prerequisite to achieve selectivity, efficiency, and catalysis in a number of metalloenzymes. Here we report on an iron(III) porphyrin with a photochromic axial ligand which, upon irradiation with two different wavelengths reversibly switches its spin state between low-spin (S = 1/2) and high-spin (S = 5/2) in solution (DMSO-acetone, 2:598). The switching efficiency is 76% at room temperature. The system is neither oxygen nor water sensitive, and no fatigue was observed after more than 1000 switching cycles. Concomitant with the spin-flip is a change in redox potential by ~60 mV. Besides serving as a simple model for the first step of the cytochrome P450 catalytic cycle, the spin switch can be used to switch the spin-lattice relaxation time T1 of the water protons by a factor of 15. Controlled switching of the spin state of transition metal ions is key in many enzymatic reactions, but difficult to replicate in synthetic systems. Here the authors report on an iron(III) porphyrin with a photochromic axial ligand that, in solution, reversibly switches between low-spin and high-spin upon irradiation with two different wavelengths.
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9
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Dhifaoui S, Hajji M, Nasri S, Guerfel T, Daran JC, Nasri H. A new high-spin iron(III) bis(aqua) complex with the meso-tetra(para-chlorophenyl)porphyrin: X-ray crystallography, Hirshfeld surface analysis, magnetic, EPR and electrochemical properties. RESEARCH ON CHEMICAL INTERMEDIATES 2018. [DOI: 10.1007/s11164-018-3555-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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10
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Synthesis, Mössbauer, cyclic voltammetry, magnetic properties and molecular structures of the low-spin iron(III) bis(pyrazine) complexes with the para-fluoro and para-chloro substituted meso-tetraphenylporphyrin. Inorganica Chim Acta 2018. [DOI: 10.1016/j.ica.2018.02.016] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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11
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Dhifaoui S, Mchiri C, Quatremare P, Marvaud V, Bujacz A, Nasri H. Molecular structure, magnetic properties, cyclic voltammetry of the low-spin iron(III) Bis(4-ethylaniline) complex with the para -chloro substituted meso -tetraphenylporphyrin. J Mol Struct 2018. [DOI: 10.1016/j.molstruc.2017.10.023] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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12
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Reiner BR, Foxman BM, Wade CR. Electrochemical and structural investigation of the interactions between naphthalene diimides and metal cations. Dalton Trans 2017; 46:9472-9480. [DOI: 10.1039/c7dt02067h] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Cyclic voltammetry and X-ray diffraction studies reveal the strength and nature of the interactions between Li+/Mg2+ and reduced naphthalene diimides.
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Affiliation(s)
| | | | - Casey R. Wade
- Department of Chemistry
- Brandeis University
- Waltham
- USA
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13
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Serth-Guzzo JA, Turowska-Tyrk I, Safo MK, Walker FA, Debrunner PG, Scheidt WR. Characterization of the mixed axial ligand complex (4-cyanopyridine)(imidazole)(tetramesitylporphinato)iron(iii) perchlorate. Stabilization by synergic bonding. J PORPHYR PHTHALOCYA 2016; 20:254-264. [DOI: 10.1142/s1088424616500206] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The reaction of [Fe(TMP)(OClO[Formula: see text]], where TMP is the dianion of tetramesitylporphyrin, with a combination of a strong [Formula: see text]-acceptor ligand and a [Formula: see text]-donating imidazole can lead to the preparation of mixed-ligand complexes [Fe(Porph)(4-CNPy)(L)][Formula: see text] where L is imidazole itself or 1-acetylimidazole and 4-cyanopyridine is the strong [Formula: see text] acceptor ligand. The stability of the new mixed-ligand pair is the presumed result of synergic bonding between the two axial ligands. The molecular structure and other characterization of the new mixed axial ligand complex, [Fe(TMP)(4-CNPy)(HIm)]ClO4 is described. The axial ligands have a relative perpendicular arrangement with Fe–N(imidazole) = 1.945 Å and Fe–N(pyridine) = 2.021 Å. The average equatorial Fe–N[Formula: see text] distance is 1.963 Å, which is consistent with the S4-ruffled TMP core. Despite the relative perpendicular arrangement of axial ligands, the EPR spectrum of the complex is a rhombic signal and not a large gmax signal. The EPR g-values are [Formula: see text] 3.05, [Formula: see text] 2.07, and [Formula: see text] 1.22. A quadrupole doublet was seen in the Mössbauer spectrum with an isomer shift of 0.197 mm/s and quadrupole splitting of 1.935 mm/s. Two crystalline forms of [Fe(TMP)(4-CNPy)(HIm)]ClO4 have been characterized; the two forms differ only in the solvent content of the lattice. Crystal data for form A: [Formula: see text] 15.432 (12) Å, [Formula: see text] 20.696 (2) Å, [Formula: see text] 19.970 (5) Å, and [Formula: see text] 99.256 (14)[Formula: see text], monoclinic, space group P21/n, V [Formula: see text] 6295 (2) Å3, Z [Formula: see text] 4, formula FeCl3O4N8C[Formula: see text]H[Formula: see text], 8397 observed data, [Formula: see text] 0.086, [Formula: see text] 0.210, refinement on [Formula: see text]. Crystal data for form B: [Formula: see text]15.267 (3) Å, [Formula: see text]20.377 (6) Å, [Formula: see text] 19.670 (4) Å, and [Formula: see text] 98.14 (1)[Formula: see text], monoclinic, space group P[Formula: see text]/n, V = 6058 (4) Å3, Z = 4, formula C[Formula: see text]H[Formula: see text]Cl[Formula: see text]FeN8O4, 5464 observed data, [Formula: see text] 0.096, [Formula: see text] 0.112, refinement on F.
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Affiliation(s)
- Judith A. Serth-Guzzo
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana USA 46556
| | - Ilona Turowska-Tyrk
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana USA 46556
| | - Martin K. Safo
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana USA 46556
| | - F. Ann Walker
- Department of Chemistry and Biochemistry, University of Arizona, Tuscon, Arizona USA 85721-0041
| | - Peter G. Debrunner
- Department of Physics, University of Illinois, Urbana, Illinois USA 61801
| | - W. Robert Scheidt
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana USA 46556
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14
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Anderson JS, Gallagher AT, Mason JA, Harris TD. A Five-Coordinate Heme Dioxygen Adduct Isolated within a Metal–Organic Framework. J Am Chem Soc 2014; 136:16489-92. [DOI: 10.1021/ja5103103] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- John S. Anderson
- Department
of Chemistry, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Audrey T. Gallagher
- Department
of Chemistry, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Jarad A. Mason
- Department
of Chemistry, University of California, Berkeley, California 94720-1460, United States
| | - T. David Harris
- Department
of Chemistry, Northwestern University, Evanston, Illinois 60208-3113, United States
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15
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Comba P, Morgen M, Wadepohl H. Tuning of the Properties of Transition-Metal Bispidine Complexes by Variation of the Basicity of the Aromatic Donor Groups. Inorg Chem 2013; 52:6481-501. [DOI: 10.1021/ic4004214] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Peter Comba
- Anorganisch-Chemisches Institut, Universität Heidelberg, INF 270, D-69120 Heidelberg, Germany
| | - Michael Morgen
- Anorganisch-Chemisches Institut, Universität Heidelberg, INF 270, D-69120 Heidelberg, Germany
| | - Hubert Wadepohl
- Anorganisch-Chemisches Institut, Universität Heidelberg, INF 270, D-69120 Heidelberg, Germany
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16
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Todorovic S, Rodrigues ML, Matos D, Pereira IAC. Redox properties of lysine- and methionine-coordinated hemes ensure downhill electron transfer in NrfH2A4 nitrite reductase. J Phys Chem B 2012; 116:5637-43. [PMID: 22519292 DOI: 10.1021/jp301356m] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The multiheme NrfHA nitrite reductase is a menaquinol:nitrite oxidoreductase that catalyzes the 6-electron reduction of nitrite to ammonia in a reaction that involves eight protons. X-ray crystallography of the enzyme from Desulfovibrio vulgaris revealed that the biological unit, NrfH2A4, houses 28 c-type heme groups, 22 of them with low spin and 6 with pentacoordinated high spin configuration. The high spin hemes, which are the electron entry and exit points of the complex, carry a highly unusual coordination for c-type hemes, lysine and methionine as proximal ligands in NrfA and NrfH, respectively. Employing redox titrations followed by X-band EPR spectroscopy and surface-enhanced resonance Raman spectroelectrochemistry, we provide the first experimental evidence for the midpoint redox potential of the NrfH menaquinol-interacting methionine-coordinated heme (-270 ± 10 mV, z = 0.96), identified by the use of the inhibitor HQNO, a structural analogue of the physiological electron donor. The redox potential of the catalytic lysine-coordinated high spin heme of NrfA is -50 ± 10 mV, z = 0.9. These values determined for the integral NrfH2A4 complex indicate that a driving force for a downhill electron transfer is ensured in this complex.
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Affiliation(s)
- Smilja Todorovic
- Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa , Av. da Republica, 2780-157 Oeiras, Portugal
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17
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Lopez MA, De La Rosa MA. Electronic effects on carbon monoxide dissociation from iron(II) tetraphenylporhyrins. J PORPHYR PHTHALOCYA 2012. [DOI: 10.1142/s1088424605000939] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
We report the kinetics of CO binding to a series of substituted ferrous tetra(4-X-phenyl)porphyrins ( X = CF 3, Cl , H , CH 3, OCH 3) in DMSO solvent using a mixture of 1,2-DMI/1-MeIm as proximal base. The CO dissociation rate constant increases with electron donation of the substituent X; the aggregate Hammett ρ value is -0.38. Using a Swain-Lupton analysis we determine the electronic effects to be transmitted 67% by through-bond or field effect and 33% by resonance. These results indicate that there is significant conjugation between the phenyl rings and the porphyrin core of iron tetraphenylporphyrin systems.
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Affiliation(s)
- Marco A. Lopez
- Department of Chemistry & Biochemistry, California State University at Long Beach, Long Beach, California, 90840, USA
| | - Martha A. De La Rosa
- Department of Chemistry & Biochemistry, California State University at Long Beach, Long Beach, California, 90840, USA
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18
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Melin F, Boudon C, Lo M, Schenk KJ, Bonin M, Ochsenbein P, Gross M, Weiss J. Electrocatalytic reduction of oxygen with phenanthroline-strapped porphyrins. J PORPHYR PHTHALOCYA 2012. [DOI: 10.1142/s1088424607000278] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The electrochemical behavior of three cytochrome c oxidase models has been investigated. All the models are derived from a phenanthroline-strapped, porphyrin framework that binds zinc(II) or iron(III) chloride in the porphyrin subunit, and copper(I) in the phenanthroline site. The iron complex and the bimetallic zinc(II) copper(I) complex of the parent ligand have been characterized by X-ray diffraction. One model consists of the parent structure on which C 12 alkyl chains have been added. This soluble model achieves electrochemical 2-electron reduction of oxygen in organic solvents without the addition of an exogenous axial base, and in the presence of an organic or inorganic source of protons. The two other models comprise the parent phenanthroline-strapped porphyrin framework, on which two pendant imidazoles have been incorporated. These models adsorbed on ring-disk electrodes with an edge-oriented, pyrolytic graphite (EOPG) disk and a platinum ring, efficiently catalyze the 4-electron reduction of oxygen in dioxygen saturated water at neutral pH.
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Affiliation(s)
- Frédéric Melin
- Chimie des ligands à Architecture Contrôlée (CLAC) Institut de Chimie, CNRS-Université Louis Pasteur, UMR 7177, 4 rue Blaise Pascal, 67070 Strasbourg, France
| | - Corinne Boudon
- Laboratoire d'Electrochimie Institut de Chimie, CNRS-Université Louis Pasteur, UMR 7177, 4 rue Blaise Pascal, 67070 Strasbourg, France
| | - Mamadou Lo
- Chimie des ligands à Architecture Contrôlée (CLAC) Institut de Chimie, CNRS-Université Louis Pasteur, UMR 7177, 4 rue Blaise Pascal, 67070 Strasbourg, France
| | - Kurt J. Schenk
- EPFL, LCr1-IPMC-FSB, BSP Dorigny, CH-1015 Lausanne, Switzerland
| | - Michel Bonin
- EPFL, LCr1-IPMC-FSB, BSP Dorigny, CH-1015 Lausanne, Switzerland
| | | | - Maurice Gross
- Laboratoire d'Electrochimie Institut de Chimie, CNRS-Université Louis Pasteur, UMR 7177, 4 rue Blaise Pascal, 67070 Strasbourg, France
| | - Jean Weiss
- Chimie des ligands à Architecture Contrôlée (CLAC) Institut de Chimie, CNRS-Université Louis Pasteur, UMR 7177, 4 rue Blaise Pascal, 67070 Strasbourg, France
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19
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Kadish KM, Finikova OS, Espinosa E, Gros CP, Stefano GD, Cheprakov AV, Beletskaya IP, Guilard R. First highly distorted π-extended Fe(II) porphyrin – a unique model to elucidate factors affecting the electrochemical potentials. J PORPHYR PHTHALOCYA 2012. [DOI: 10.1142/s108842460400043x] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The preparation, X-ray crystal structure and electrochemistry of a new poly-substituted air-stable tetrabenzoporphyrin iron(II) bis-pyridine complex (1) is reported.
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Affiliation(s)
- Karl M. Kadish
- Department of Chemistry, University of Houston, Houston, Texas 77204-5003, USA
| | - Olga S. Finikova
- Department of Chemistry, Moscow State University, Moscow 119899, Russia
| | - Enrique Espinosa
- LIMSAG (Laboratoire d'Ingénierie Moléculaire pour la Séparation et les Applications des Gaz, UMR 5633), Université de Bourgogne, Faculté des Sciences Gabriel, 6 boulevard Gabriel, 21000 Dijon, France
| | - Claude P. Gros
- LIMSAG (Laboratoire d'Ingénierie Moléculaire pour la Séparation et les Applications des Gaz, UMR 5633), Université de Bourgogne, Faculté des Sciences Gabriel, 6 boulevard Gabriel, 21000 Dijon, France
| | - Guido De Stefano
- Department of Chemistry, University of Houston, Houston, Texas 77204-5003, USA
| | | | | | - Roger Guilard
- LIMSAG (Laboratoire d'Ingénierie Moléculaire pour la Séparation et les Applications des Gaz, UMR 5633), Université de Bourgogne, Faculté des Sciences Gabriel, 6 boulevard Gabriel, 21000 Dijon, France
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20
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Taesch J, Dang TT, Heitz V. Efficient synthesis and Suzuki cross-coupling reactions of meso-tetrakis(2,6-dimethyl-4-triflyloxyphenyl)porphyrin. Tetrahedron Lett 2012. [DOI: 10.1016/j.tetlet.2011.11.045] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/15/2022]
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21
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Sturms R, Kakar S, Trent J, Hargrove MS. Trema and parasponia hemoglobins reveal convergent evolution of oxygen transport in plants. Biochemistry 2010; 49:4085-93. [PMID: 20377207 DOI: 10.1021/bi1002844] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
All plants contain hemoglobins that fall into distinct phylogenetic classes. The subset of plants that carry out symbiotic nitrogen fixation expresses hemoglobins that scavenge and transport oxygen to bacterial symbiotes within root nodules. These "symbiotic" oxygen transport hemoglobins are distinct in structure and function from the nonoxygen transport ("nonsymbiotic") Hbs found in all plants. Hemoglobins found in two closely related plants present a paradox concerning hemoglobin structure and function. Parasponia andersonii is a nitrogen-fixing plant that expresses a symbiotic hemoglobin (ParaHb) characteristic of oxygen transport hemoglobins in having a pentacoordinate ferrous heme iron, moderate oxygen affinity, and a relatively rapid oxygen dissociation rate constant. A close relative that does not fix nitrogen, Trema tomentosa, expresses hemoglobin (TremaHb) sharing 93% amino acid identity to ParaHb, but its phylogeny predicts a typical nonsymbiotic hemoglobin with a hexacoordinate heme iron, high oxygen affinity, and slow oxygen dissociation rate constant. Here we characterize heme coordination and oxygen binding in TremaHb and ParaHb to investigate whether or not two hemoglobins with such high sequence similarity are actually so different in functional behavior. Our results indicate that the two proteins resemble nonsymbiotic hemoglobins in the ferric oxidation state and symbiotic hemoglobins in the ferrous oxidation state. They differ from each other only in oxygen affinity and oxygen dissociation rate constants, two factors key to their different functions. These results demonstrate distinct mechanisms for convergent evolution of oxygen transport in different phylogenetic classes of plant hemoglobins.
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Affiliation(s)
- Ryan Sturms
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa 50011, USA
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22
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Ryabov AD, Collins TJ. Mechanistic considerations on the reactivity of green FeIII-TAML activators of peroxides. ADVANCES IN INORGANIC CHEMISTRY 2009. [DOI: 10.1016/s0898-8838(09)00208-6] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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23
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Fufezan C, Zhang J, Gunner MR. Ligand preference and orientation in b- and c-type heme-binding proteins. Proteins 2008; 73:690-704. [PMID: 18491383 DOI: 10.1002/prot.22097] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Hemes are often incorporated into designed proteins. The importance of the heme ligand type and its orientation is still a matter of debate. Here, heme ligands and ligand orientation were investigated using a nonredundant (87 structures) and a redundant (1503 structures) set of structures to compare and contrast design features of natural b- and c-type heme-binding proteins. Histidine is the most common ligand. Marked differences in ligation motifs between b- and c-type hemes are higher occurrence of His-Met in c-type heme binding motifs (16.4% vs. 1.4%) and higher occurrence of exchangeable, small molecules in b-type heme binding motifs (67.6% vs. 9.9%). Histidine ligands that are part of the c-type CXXCH heme-binding motif show a distinct asymmetric distribution of orientation. They tend to point between either the heme propionates or between the NA and NB heme nitrogens. Molecular mechanics calculations show that this asymmetry is due to the bonded constraints of the covalent attachment between the heme and the protein. In contrast, the orientations of b-type hemes histidine ligands are found evenly distributed with no preference. Observed histidine heme ligand orientations show no dominating influence of electrostatic interactions between the heme propionates and the ligands. Furthermore, ligands in bis-His hemes are found more frequently perpendicular rather than parallel to each other. These correlations support energetic constraints on ligands that can be used in designing proteins.
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Affiliation(s)
- Christian Fufezan
- Physics Department, City College of New York, New York, New York 10031, USA.
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24
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Behera S, Raj CR. Electrochemistry of surface wired redox protein: Axial ligation and control of redox potential. J Electroanal Chem (Lausanne) 2008. [DOI: 10.1016/j.jelechem.2008.04.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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25
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Reedy CJ, Elvekrog MM, Gibney BR. Development of a heme protein structure-electrochemical function database. Nucleic Acids Res 2007; 36:D307-13. [PMID: 17933771 PMCID: PMC2238922 DOI: 10.1093/nar/gkm814] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Proteins containing heme, iron(protoporphyrin IX) and its variants, continue to be one of the most-studied classes of biomolecules due to their diverse range of biological functions. The literature is abundant with reports of structural and functional characterization of individual heme proteins which demonstrate that heme protein reduction potential values, Em, span the range from –550 mV to +450 mV versus SHE. In order to unite these data for the purposes of global analysis, a new web-based resource of heme protein structure–function relationships is presented: the Heme Protein Database (HPD). This database is the first of its kind to combine heme protein structural classifications including protein fold, heme type and heme axial ligands, with heme protein reduction potential values in a web-searchable format. The HPD is located at http://heme.chem.columbia.edu/heme.php. The data illustrate that heme protein Em values are modulated over a 300 mV range by the type of global protein fold, a 600 mV range by the type of porphyrin and an 800 mV range by the axial ligands. Thus, the 1 V range observed in heme protein reduction potential values in biological systems arises from subtle combinations of these various factors.
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Affiliation(s)
- Charles J Reedy
- Department of Chemistry, Columbia University, 3000 Broadway, MC 3121, New York, NY 10027, USA
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26
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Marques HM. Insights into porphyrin chemistry provided by the microperoxidases, the haempeptides derived from cytochrome c. Dalton Trans 2007:4371-85. [PMID: 17909648 DOI: 10.1039/b710940g] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The water-soluble haem-containing peptides obtained by proteolytic digestion of cytochrome c, the microperoxidases, have been used to explore aspects of the chemistry of iron porphyrins, and as mimics for some reactions catalysed by the haemoproteins, including the reactions catalysed by the peroxidases and the cytochromes P450. The preparation of the microperoxidases, their physical and chemical properties including their electronic structure, the kinetics and thermodynamics of their reactions with ligands, electrochemical studies and examples of their uses as haemoproteins mimics, is reviewed.
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Affiliation(s)
- Helder M Marques
- Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, Johannesburg 2050, South Africa.
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27
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Hoy JA, Smagghe BJ, Halder P, Hargrove MS. Covalent heme attachment in Synechocystis hemoglobin is required to prevent ferrous heme dissociation. Protein Sci 2007; 16:250-60. [PMID: 17242429 PMCID: PMC2203299 DOI: 10.1110/ps.062572607] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Synechocystis hemoglobin contains an unprecedented covalent bond between a nonaxial histidine side chain (H117) and the heme 2-vinyl. This bond has been previously shown to stabilize the ferric protein against denaturation, and also to affect the kinetics of cyanide association. However, it is unclear why Synechocystis hemoglobin would require the additional degree of stabilization accompanying the His117-heme 2-vinyl bond because it also displays endogenous bis-histidyl axial heme coordination, which should greatly assist heme retention. Furthermore, the mechanism by which the His117-heme 2-vinyl bond affects ligand binding has not been reported, nor has any investigation of the role of this bond on the structure and function of the protein in the ferrous oxidation state. Here we report an investigation of the role of the Synechocystis hemoglobin His117-heme 2-vinyl bond on structure, heme coordination, exogenous ligand binding, and stability in both the ferrous and ferric oxidation states. Our results reveal that hexacoordinate Synechocystis hemoglobin lacking this bond is less stable in the ferrous oxidation state than the ferric, which is surprising in light of our understanding of pentacoordinate Hb stability, in which the ferric protein is always less stable. It is also demonstrated that removal of the His117-heme 2-vinyl bond increases the affinity constant for intramolecular histidine coordination in the ferric oxidation state, thus presenting greater competition for the ligand binding site and lowering the observed rate and affinity constants for exogenous ligands.
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Affiliation(s)
- Julie A Hoy
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA 50011, USA
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28
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Halder P, Trent JT, Hargrove MS. Influence of the protein matrix on intramolecular histidine ligation in ferric and ferrous hexacoordinate hemoglobins. Proteins 2007; 66:172-82. [PMID: 17044063 DOI: 10.1002/prot.21210] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Present in most organisms, hexacoordinate hemoglobins (hxHbs) are proteins that have evolved the capacity for reversible bis-histidyl heme coordination. The heme prosthetic group enables diverse protein functionality, such as electron transfer, redox reactions, ligand transport, and enzymatic catalysis. The reactivity of heme is greatly effected by the coordination and noncovalent chemical environment imposed by its connate protein. Of considerable interest is how the hxHb globin fold achieves reversible intramolecular coordination while still enabling high-affinity binding of oxygen, nitric oxide, and other small ligands. Here we explore this question by examining the role of the protein matrix on coordination behavior in a group of hxHbs from animals, plants, and bacteria, including human neuroglobin and cytoglobin, a nonsymbiotic hemoglobin from rice, and a truncated hemoglobin from the cyanobacterium Synechocystis. This is done with a set of experiments measuring the reduction potentials of each wild-type hxHb and its corresponding mutant protein where the reversibly bound histidine (the distal His) has been replaced with a noncoordinating side chain. These reduction potentials, coupled with studies of the mutant proteins saturated with exogenous imidazole, enable us to assess the effects of the protein matrices on histidine coordination. Our results show significant variation among the hxHbs, demonstrating flexibility in the globin moiety's ability to regulate reversible coordination. This regulation is particularly evident in the plant nonsymbiotic hemoglobins, where ferric state histidine coordination affinity is substantially lowered by the protein matrix.
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Affiliation(s)
- Puspita Halder
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa 50011, USA
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29
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Vashi PR, Marques HM. The coordination of imidazole and substituted pyridines by the hemeoctapeptide N-acetyl-ferromicroperoxidase-8 (FeIINAcMP8). J Inorg Biochem 2005; 98:1471-82. [PMID: 15337599 DOI: 10.1016/j.jinorgbio.2004.05.016] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2004] [Revised: 05/11/2004] [Accepted: 05/18/2004] [Indexed: 11/23/2022]
Abstract
The N-terminus acetylated ferric hemeoctapeptide from cytochrome c, N-acetylmicroperoxidase-8 (Fe(III)-NAcMP8) can be reduced by dithionite in aqueous solution to produce Fe(II)-NAcMP8. The UV-Vis spectrum has a broad Soret band and relatively poorly defined Q bands which is consistent with a mixture of a five-coordinate high spin species with His as the axial ligand and a six-coordinate, predominantly high spin species with His/H(2)O as axial ligands. There are two spectroscopically observable pK(a)s at 8.7+/-0.1 and 10.9+/-0.2 which are attributed to ionization of a heme propionic acid group and coordinated H(2)O, respectively; a pK(a) > or = 14 is due to ionization of the proximal His ligand. Equilibrium constants were determined by UV-Vis spectrophotometry at 25.0+/-0.2 degrees C and 0.5 M ionic strength (NaClO(4)) for the coordination of imidazole and a number of substituted pyridines, and complement available data for the ferric hemepeptide, allowing a comparison to be made of the affinity of an iron porphyrin with Fe in the +2 and +3 oxidation states towards these ligands. Imidazole is coordinated more strongly by the ferric porphyrin (log K=4.08) than by the ferrous porphyrin (log K=3.40). The equilibrium constants for coordination of pyridines by the ferric and ferrous porphyrins increase and decrease, respectively, with increasing ligand basicity. Values determined by cyclic voltammetry show the same dependence on the identity of the ligand. In the ferric porphyrin, the stability of the complex increases with the basicity of the ligand and hence its ability to donate electron density onto the metal. In the case of the more electron rich ferrous porphyrin, greater stability occurs with pyridine ligands that have an electron withdrawing group and hence can accept electron density from the metal. This is consistent with the midpoint reduction potentials E(1/2) of the pyridine complexes determined by cyclic voltammetry; E(1/2) is linearly dependent on, and becomes more negative with an increase in, ligand basicity. Log K for coordination of pyridines by the ferrous hemepeptide correlates well with the energy of the ligand frontier orbital with pi symmetry, suggesting that pi-bonding effects are significant in determining the strength of binding of pyridines by a ferrous porphyrin.
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Affiliation(s)
- Preeti R Vashi
- Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, P.O. Wits, Johannesburg 2050, South Africa
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30
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Hu C, Noll BC, Schulz CE, Scheidt WR. Ligand orientation control in low-spin six-coordinate (porphinato)iron(II) species. Inorg Chem 2005; 44:4346-58. [PMID: 15934765 PMCID: PMC1502394 DOI: 10.1021/ic050320p] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The synthesis of a low-spin six-coordinate iron(II) porphyrinate in which the two axial ligands are forced to have a relative perpendicular orientation has been successfully accomplished for the first time. The reaction of four-coordinate (tetramesitylporphinato)iron(II) with 2-methylimidazole leads to the preparation of [Fe(TMP)(2-MeHIm)(2)] which cocrystallizes with five-coordinate [Fe(TMP)(2-MeHIm)]. The six-coordinate complex accommodates the sterically crowded pair of imidazoles with a strongly ruffled core and relative perpendicular orientation. This leads to shortened equatorial bonds of 1.963(6) A and slightly elongated axial Fe-N bond lengths of 2.034(9) A that are about 0.04 A shorter and 0.03 A longer, respectively, in comparison to those of the bis-imidazole-ligated iron(II) species with parallel oriented axial ligands. The Mossbauer spectrum shows a pair of quadrupole doublets that can be assigned to the components of the cocrystallized crystalline solid. High-spin five-coordinate [Fe(TMP)(2-MeHIm)] has DeltaE(Q) = 2.25 mm/s and delta = 0.90 mm/s at 15 K. The quadrupole splitting, DeltaE(Q), for [Fe(TMP)(2-MeHIm)(2)] is 1.71 mm/s, and the isomer shift is 0.43 mm/s at 15 K. The quadrupole splitting value is significantly larger than that found for low-spin iron(II) derivatives with relative parallel orientations for the two axial ligands. Mossbauer spectra thus provide a probe for ligand orientation when structural data are otherwise not available.
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Affiliation(s)
- Chuanjiang Hu
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, USA
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31
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Denisov IG, Makris TM, Sligar SG, Schlichting I. Structure and Chemistry of Cytochrome P450. Chem Rev 2005; 105:2253-77. [PMID: 15941214 DOI: 10.1021/cr0307143] [Citation(s) in RCA: 1510] [Impact Index Per Article: 79.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Ilia G Denisov
- Department of Biochemistry, Center for Biophysics and Computational Biology, University of Illinois, Urbana-Champaign, 61801, USA
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32
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Galstyan AS, Zarić SD, Knapp EW. Computational studies on imidazole heme conformations. J Biol Inorg Chem 2005; 10:343-54. [PMID: 15843984 DOI: 10.1007/s00775-005-0642-8] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2004] [Accepted: 03/09/2005] [Indexed: 11/25/2022]
Abstract
Density functional theory computations of heme with ionized propionic acid groups, axially coordinated with two imidazoles, were performed for different mutual orientations of the imidazole planes. Environmental influences from water or protein were considered with a continuum dielectric medium by solving the Poisson equation. In vacuum, optimized geometries yielded imidazole-heme conformations where the NH groups of imidazoles are oriented toward the heme propionic groups in agreement with data from crystal structures of heme proteins. Conformational free-energy dependencies of the mutual orientation of axially ligated imidazoles calculated in protein (epsilon=10) and water (epsilon=80) environments confirmed the vacuum results, albeit the energy difference between the preferred and the 180 degrees opposite orientations of the imidazole ligand decreased from 3.84 kcal/mol in vacuum to 2.35 and 2.40 kcal/mol in protein and water, respectively. Two main factors determine the imidazole orientation: (1) the direct intramolecular electrostatic interactions of propionic groups with the polar NH groups of imidazole and (2) the electrostatic interaction of the total dipole moment of the imidazole-heme complex with the reaction field. In vacuum, only the first type of interaction is present, while in a dielectric medium the latter effect becomes competitive at high dielectric constant, resulting in a decrease of the orientational preference. Interestingly, the orientational preference of the imidazole axially ligated to heme becomes even more pronounced, if the negatively charged propionates are neutralized by counter charges that mimic salt bridges or protonation of the propionates.
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Affiliation(s)
- Artur S Galstyan
- Institute of Chemistry, Department of Biology, Chemistry, and Pharmacy, Free University of Berlin, Takustrasse 6, 14195 Berlin, Germany
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33
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Ryabova ES, Rydberg P, Kolberg M, Harbitz E, Barra AL, Ryde U, Andersson KK, Nordlander E. A comparative reactivity study of microperoxidases based on hemin, mesohemin and deuterohemin. J Inorg Biochem 2005; 99:852-63. [PMID: 15708807 DOI: 10.1016/j.jinorgbio.2004.12.020] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2004] [Revised: 12/22/2004] [Accepted: 12/24/2004] [Indexed: 11/28/2022]
Abstract
Three microperoxidases--hemin-6(7)-gly-gly-his methyl ester (HGGH), mesohemin-6(7)-gly-gly-his methyl ester (MGGH) and deuterohemin-6(7)-gly-gly-his methyl ester (DGGH)--have been prepared as models for heme-containing peroxidases by condensation of glycyl-glycyl-L-histidine methyl ester with the propionic side chains of hemin, mesohemin and deuterohemin, respectively. The three microperoxidases differ in two substituents, R, of the protoporphyrin IX framework (HGGH: R=vinyl, MGGH: R=ethyl, DGGH: R=H). X-band and high field EPR spectra show that the microperoxidases exhibit spectroscopic properties similar to those of metmyoglobin, i.e. a high spin ferric S=5/2 signal at g(perpendicular)=6 and g parallel)=2 and an estimated D value of 7.5+/-1cm(-1). The catalytic activities of the microperoxidases towards K4[Fe(CN)6], L-tyrosine methyl ester and 2,2'-azino(bis(3-ethylbenzothiazoline-6-sulfonic acid)) (ABTS) have been investigated. It was found that all three microperoxidases exhibit peroxidase activity and that the reactions follow the generally accepted peroxidase reaction scheme [Biochem. J. 145 (1975) 93-103] with the exception that the initial formation of a Compound I analogue is the rate-limiting step for the whole process. The general activity trend was found to be MGGH approximately DGGH>HGGH. For each microperoxidase, DFT calculations (B3LYP) were made on the reactions of compounds 0, I and II with H+, e- and H+ + e-, respectively, in order to probe the possible relationship between the nature of the 2- and 4-substituents of the hemin and the observed reactivity. The computational modeling indicates that the relative energy differences are very small; solvation and electrostatic effects may be factors that decide the relative activities of the microperoxidases.
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Affiliation(s)
- Ekaterina S Ryabova
- Inorganic Chemistry, Center for Chemistry and Chemical Engineering, Lund University, Box 124, SE-221 00 Lund, Sweden
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Affiliation(s)
- Charles J Reedy
- Department of Chemistry, Columbia University, 3000 Broadway, MC 3121, New York, New York 10027, USA
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Ryabova ES, Dikiy A, Hesslein AE, Bjerrum MJ, Ciurli S, Nordlander E. Preparation and reactivity studies of synthetic microperoxidases containing b-type heme. J Biol Inorg Chem 2004; 9:385-95. [PMID: 15042435 DOI: 10.1007/s00775-004-0532-5] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2003] [Accepted: 02/19/2004] [Indexed: 10/26/2022]
Abstract
In order to create a heme environment that permits biomimicry of heme-containing peroxidases, a number of new hemin-peptide complexes--hemin-2(18)-glycyl-L-histidine methyl ester (HGH), hemin-2(18)-glycyl-glycyl-L-histidine methyl ester (HGGH), and hemin-2,18-bis(glycyl-glycyl-L-histidine methyl ester) (H2GGH)--have been prepared by condensation of glycyl-L-histidine methyl ester or glycyl-glycyl-L-histidine methyl ester with the propionic side chains of hemin. Characterization by means of UV/vis- and 1H NMR spectroscopy as well as cyclic- and differential pulse voltammetry indicates the formation of five-coordinate complexes in the case of HGH and HGGH, with histidine as an axial ligand. In the case of H2GGH, a six-coordinate complex with both imidazoles coordinated to the iron center appears to be formed. However, 1H NMR of H2GGH reveals the existence of an equilibrium between low-spin six-coordinate and high-spin five-coordinate species in solution. The catalytic activity of the hemin-peptide complexes towards several organic substrates, such as p-cresol, L-tyrosine methyl ester, and ABTS, has been investigated. It was found that not only the five-coordinate HGH and HGGH complexes, but also the six-coordinate H2GGH, catalyze the oxidation of substrates by H2O2. The longer and less strained peptide arm provides the HGGH complex with a slightly higher catalytic efficiency, as compared with HGH, due to formation of more stable intermediate complexes.
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Affiliation(s)
- Ekaterina S Ryabova
- Inorganic Chemistry, Chemical Center, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden
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Walker FA. Models of the Bis-Histidine-Ligated Electron-Transferring Cytochromes. Comparative Geometric and Electronic Structure of Low-Spin Ferro- and Ferrihemes. Chem Rev 2004; 104:589-615. [PMID: 14871136 DOI: 10.1021/cr020634j] [Citation(s) in RCA: 176] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- F Ann Walker
- Department of Chemistry, University of Arizona, Tucson, Arizona 85721-0041, USA.
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Bley-Escrich J, Gisselbrecht JP, Michels M, Zander L, Vogel E, Gross M. Electrochemical and Spectroelectrochemical Investigations of Mono- and Binuclear Cobalt(II) Complexes of“Figure-Eight” Octapyrrolic Macrocycles. Eur J Inorg Chem 2004. [DOI: 10.1002/ejic.200300499] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Picaud T, Le Moigne C, Loock B, Momenteau M, Desbois A. Nonplanar distortions of bis-base low-spin iron(II)-porphyrinates: absorption and resonance Raman investigations of cross-trans-linked iron(II)-basket-handle porphyrin complexes. J Am Chem Soc 2003; 125:11616-25. [PMID: 13129366 DOI: 10.1021/ja034710r] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Electronic absorption and Soret-excited resonance Raman (RR) spectra are reported for bis-N-alkylimidazole and bis-pyridine complexes of various cross-trans-linked iron(II)-"basket-handle" porphyrins (Fe(II)-BHP) in methylene chloride. These compounds enable us to characterize the spectroscopic properties of ruffled six-coordinated low-spin Fe(II)-porphyrin complexes. The visible absorption spectra show that the Q and B bands are progressively red-shifted when the handles are shortened and/or when the steric hindrance of the axial ligands is increased. This effect is accompanied by both a decrease in RR frequency of the nu(2) mode and an increase in frequency of the nu(8) and nu(s)(Fe-ligand(2)) modes. More precisely, an inverse linear correlation is found between the frequencies of the nu(2) and nu(8) modes. For each ligation state, the positions of the absorption bands are also linearly correlated with the frequency of the nu(2) or nu(8) mode. All of these spectroscopic data reveal that the degree of ruffling of the Fe(II)-BHP complexes is increased by the N-methylimidazole --> pyridine axial substitutions, presumably because the mutual steric strains between the axial ligand rings, the porphyrin macrocycle and the porphyrin handles are increased. The present study provides a first basis for discerning ruffled conformations from planar and other nonplanar structures in ferrous heme proteins.
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Affiliation(s)
- Thierry Picaud
- Département de Biologie Joliot-Curie, SBFM, CEA et URA CNRS 2096, CEA/Saclay, F-91191 Gif-sur-Yvette Cedex, France
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Medaković V, Zarić SD. Theoretical study on orientations of axially coordinated imidazoles in model systems of cytochromes. Inorganica Chim Acta 2003. [DOI: 10.1016/s0020-1693(03)00086-0] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Shokhireva TK, Berry RE, Uno E, Balfour CA, Zhang H, Walker FA. Electrochemical and NMR spectroscopic studies of distal pocket mutants of nitrophorin 2: stability, structure, and dynamics of axial ligand complexes. Proc Natl Acad Sci U S A 2003; 100:3778-83. [PMID: 12642672 PMCID: PMC152998 DOI: 10.1073/pnas.0536641100] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
WT and leucine --> valine distal pocket mutants of nitrophorin 2 (NP2) and their NO complexes have been investigated by spectroelectrochemistry. NO complexes of two of the mutants exhibit more positive reduction potential shifts than does the WT protein, thus indicating stabilization of the Fe(II)-NO state. This more positive reduction potential for NP2-L132V and the double mutant is consistent with the hypothesis that smaller valine residues may allow the heme to regain planarity instead of being significantly ruffled, as in WT NP2. Thus, ruffling may stabilize the Fe(III)-NO state, which is required for facile NO dissociation. NMR spectroscopic investigations show that the sterically demanding 2-methylimidazole ligand readily binds to all three distal pocket mutants to create low-spin Fe(III) complexes having axial ligands in nearly perpendicular planes; it also binds to the WT protein in the presence of higher concentrations of 2-methylimidazole, but yields a different ligand plane orientation than is present in any of the three distal pocket mutants. NOESY spectra of NP2-ImH mutants exhibit chemical exchange cross peaks, whereas WT NP2-ImH shows no chemical exchange. Chemical exchange in the case of the distal leucine --> valine mutants is caused by ImH ligand orientational dynamics. The two angular orientations of the ImH ligand could be determined from the (1)H chemical shifts of the heme methyls, and the rate of interconversion of the two forms could be estimated from the NOESY diagonal and cross peak intensities. K(eq) is 100 or larger and favors an orientation similar to that found for the WT NP2-ImH complex.
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41
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Simkhovich L, Goldberg I, Gross Z. Iron(III) and iron(IV) corroles: synthesis, spectroscopy, structures, and no indications for corrole radicals. Inorg Chem 2002; 41:5433-9. [PMID: 12377038 DOI: 10.1021/ic020118b] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A delicate control of reaction conditions allows the isolation of several distinctively different iron complexes of tris(pentafluorophenyl)- and tris(2,6-dichlorophenyl)corrole. As long as coordinating ligands are present, the iron(III) complexes are stable in solution. Otherwise they are aerobically oxidized to either mononuclear chloroiron(IV) or dinuclear (mu-oxo)iron(IV) complexes, in acidic and basic solutions, respectively (the latter holds only for tris(pentafluorophenyl)corrole). When treated with NaNO(2), the mononuclear chloroiron(IV) corroles are efficiently converted into diamagnetic iron nitrosyl complexes. The low- and intermediate-spin iron(III), iron nitrosyl, and chloroiron(IV) corroles were fully characterized by a combination of spectroscopic methods and X-ray crystallography. There was no indication for an open-shell corrole in any of the complexes.
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Affiliation(s)
- Liliya Simkhovich
- Department of Chemistry, Institute of Catalysis Science and Technology, Technion-Israel Institute of Technology, Haifa 32000, Israel
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Ellison MK, Schulz CE, Scheidt WR. Structure of the deoxymyoglobin model [Fe(TPP)(2-MeHIm)] reveals unusual porphyrin core distortions. Inorg Chem 2002; 41:2173-81. [PMID: 11952371 DOI: 10.1021/ic020012g] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The preparation and characterization of the deoxymyoglobin model (2-methylimidazole)(tetraphenylporphinato)iron(II) is described. The preparation and crystallization from chlorobenzene leads to a new crystalline phase that has been structurally characterized. The complex is the most ordered example of a deoxymyoglobin model yet characterized. The X-ray structure determination reveals a number of distortions both in the iron coordination group and in the porphyrin core that result from the steric bulk of the axial ligand. Some of these distortions have been noted previously in related species; however, the demonstration of porphyrin core distortions and an asymmetry in the Fe-N(p) bond distances are new observations. These may have functional significance for this important type of heme protein coordination group. The new structure emphasizes that high-spin iron(II) porphyrinate derivatives display substantial structural pliability with significant variations in iron atom displacements, porphyrin core hole size, and axial and equatorial Fe-N bond lengths. The new complex has also been characterized by zero-field and applied field magnetic Mössbauer spectroscopy. Mössbauer parameters are characteristic for high-spin iron, although they also reveal an extremely rhombic site for iron(II). Crystal data at 130 K for [Fe(TPP)(2-MeHIm)].1.5C(6)H(5)Cl: a = 12.334(3) A, b = 13.515(6) A, c = 14.241(7) A, alpha = 70.62(3) degrees, beta = 88.29(2) degrees, gamma = 88.24(3) degrees, triclinic, space group, P, V = 2238(2) A(3), Z = 2.
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Affiliation(s)
- Mary K Ellison
- The Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, USA
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Ferrali M, Donati D, Bambagioni S, Fontani M, Giorgi G, Pietrangelo A. 3-Hydroxy-(4H)-benzopyran-4-ones as potential iron chelating agents in vivo. Bioorg Med Chem 2001; 9:3041-7. [PMID: 11597487 DOI: 10.1016/s0968-0896(01)00207-3] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Increasing evidence suggests that iron plays an important role in tissue damage both during chronic iron overload diseases (i.e., hemochromatosis) and when, in the absence of actual tissue iron overload, iron is delocalised from specific carriers or intracellular sites (inflammation, neurodegenerative diseases, post-ischaemic reperfusion, etc.). In order to be used for therapeutical purposes in vivo, a reliable iron chelator should be capable of preventing the undesired effects that follow the electrochemical activation of iron (see below). Bearing in mind the molecular structure of some flavonols that are able to chelate iron, we synthesised a new oral iron-chelator, 2-methyl-3-hydroxy-4H-benzopyran-4-one (MCOH). We demonstrate that MCOH chelates iron in a 2:1 ratio showing a stability constant of approximately 10(10). MCOH is able to cross cell membranes (erythrocytes, ascite tumour cells) in both directions. Following intraperitoneal administration to rats, it is quickly taken up by the liver and excreted in the urine within 24h. A similar behaviour has been documented after oral administration. We propose that MCOH may represent the prototype of a new class of iron chelating agents to be developed for iron-removal therapy in vivo with the goal of preventing tissue damage caused by the iron redox cycle.
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Affiliation(s)
- M Ferrali
- Department of Physiopathology and Experimental Medicine, Siena University, via A.Moro, 53100, Siena, Italy.
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Kennedy ML, Silchenko S, Houndonougbo N, Gibney BR, Dutton PL, Rodgers KR, Benson DR. Model hemoprotein reduction potentials: the effects of histidine-to-iron coordination equilibrium. J Am Chem Soc 2001; 123:4635-6. [PMID: 11457264 DOI: 10.1021/ja0156441] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- M L Kennedy
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, USA
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Patel N, Jones DK, Raven EL. Investigation of the haem-nicotinate interaction in leghaemoglobin. Role of hydrogen bonding. EUROPEAN JOURNAL OF BIOCHEMISTRY 2000; 267:2581-7. [PMID: 10785378 DOI: 10.1046/j.1432-1327.2000.01267.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
A strategic assessment of the contributions of two active-site hydrogen bonds in the binding of nicotinate to recombinant ferric soybean leghaemoglobin a (rLb) was carried out by mutagenic replacement of the hydrogen-bonding residues (H61A and Y30A variants) and by complementary chemical substitution of the carboxylate functionality on the nicotinate ligand. Dissociation constants, Kd (pH 5.5, mu = 0.10 M, 25.0 +/- 0.1 degrees C), for binding of nicotinate to ferric rLb, H61A and Y30A were 1.4 +/- 0.3 microM, 19 +/- 1 microM and 11 +/- 1 microM, respectively; dissociation constants for binding of nicotinamide were, respectively, 38 +/- 1 mM, 50 +/- 2 mM and 12 +/- 1 mM, and for binding of pyridine were 260 +/- 50 microM, 4.5 +/- 0.5 microM and 66 +/- 8 microM, respectively. Binding of cyanide and azide to the H61A and Y30A variants was unaffected by the mutations. The pH-dependence of nicotinate binding for rLb and Y30A was consistent with a single titration process (pKa values 6.9 +/- 0.1 and 6.7 +/- 0.2, respectively); binding of nicotinate to H61A was independent of pH. Reduction potentials for the rLb and rLb-nicotinate derivatives were 29 +/- 2 mV (pH 5.40, 25.0 degrees C, mu = 0.10 M) and - 65 +/- 2 mV (pH 5.42, 25.0 degrees C, mu = 0.10 M), respectively. The experiments provide a quantitative assessment of the role of individual hydrogen bonds in the binding process, together with a definitive determination of the pKa of His61 and unambiguous evidence that titration of His61 controls binding in the neutral to alkaline region.
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Affiliation(s)
- N Patel
- Department of Chemistry, University of Leicester, UK
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Nesset MJ, Cai S, Shokhireva TK, Shokhirev NV, Jacobson SE, Jayaraj K, Gold A, Walker FA. Electronic effects in transition metal porphyrins. 10. Effect of ortho substituents on the temperature dependence of the NMR spectra of a series of spin-admixed perchloratoiron(III) tetrakis(2,6- or 2,4,6-phenyl substituted)porphyrinates. Inorg Chem 2000; 39:532-40. [PMID: 11229573 DOI: 10.1021/ic9907866] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The perchloratoiron(III) complexes of a series of 2,6-disubstituted tetraphenylporphyrin ligands, where the 2,6-phenyl substituents were -H, -F, -Cl, -Br, or -OMe, as well as two 2,4,6-phenyl-substituted complexes, where the substituents were -Me and -OMe, have been investigated as a function of temperature by 1H NMR spectroscopy. Curvature in the 1/T dependence was evident in most cases. Forced linear extrapolation of the temperature dependence observed over the range of the study yielded Curie plots that include negative slopes with very large positive 1/T intercepts (Cl approximately Br > Me > H) to negative slope with near zero intercept (tri-OMe) to positive slope with very large negative intercept (F, di-OMe). The NMR results were combined with EPR spectroscopic data and curve-fitting procedures based on an expanded Curie law to arrive at a consistent overview of the variety of temperature-dependence behaviors observed. This overview relies upon the premise that, in addition to the ground state observed by EPR spectroscopy, one (or more) thermally accessible excited state(s) are populated to varying degrees over the temperature range of the NMR measurements. If only one excited state is considered, the analysis is consistent with the ground state being a largely intermediate-spin state (S = 3/2) for the majority of the complexes but a largely high-spin state (S = 5/2) for ((2,6-F2)4TPP)FeOClO3 and ((2,6-(OMe)2)4TPP)FeOClO3.
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Affiliation(s)
- M J Nesset
- Department of Chemistry, University of Arizona, Tucson 85721, USA
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Ann Walker F, Montfort WR. The nitric oxide-releasing heme proteins from the saliva of the blood-sucking insect Rhodnius prolixus. ADVANCES IN INORGANIC CHEMISTRY 2000. [DOI: 10.1016/s0898-8838(00)51006-x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Weyermann P, Gisselbrecht JP, Boudon C, Diederich F, Gross M. Dendritische Eisenporphyrine mit kovalent fixierten axialen Liganden: neue Modellsysteme für Cytochrome. Angew Chem Int Ed Engl 1999. [DOI: 10.1002/(sici)1521-3757(19991102)111:21<3400::aid-ange3400>3.0.co;2-7] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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49
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Araki K, Toma HE. Electrochemistry of a tetraruthenated iron porphyrin and its electrostatically assembled bilayered films. Electrochim Acta 1999. [DOI: 10.1016/s0013-4686(98)00281-3] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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50
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Momot KI, Walker FA. Rate Constants and Thermodynamic Parameters of Rotation of Axial Ligands in a Bisligated Ferric Tetramesitylporphyrinate Complex Measured from the Temperature Dependence of 1H Transverse Relaxation Rates. J Phys Chem A 1998. [DOI: 10.1021/jp982892j] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
| | - F. Ann Walker
- Department of Chemistry, University of Arizona, Tucson, Arizona 85721
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