1
|
Tarrago M, Römelt C, Nehrkorn J, Schnegg A, Neese F, Bill E, Ye S. Experimental and Theoretical Evidence for an Unusual Almost Triply Degenerate Electronic Ground State of Ferrous Tetraphenylporphyrin. Inorg Chem 2021; 60:4966-4985. [PMID: 33739093 DOI: 10.1021/acs.inorgchem.1c00031] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Iron porphyrins exhibit unrivalled catalytic activity for electrochemical CO2-to-CO conversion. Despite intensive experimental and computational studies in the last 4 decades, the exact nature of the prototypical square-planar [FeII(TPP)] complex (1; TPP2- = tetraphenylporphyrinate dianion) remained highly debated. Specifically, its intermediate-spin (S = 1) ground state was contradictorily assigned to either a nondegenerate 3A2g state with a (dxy)2(dz2)2(dxz,yz)2 configuration or a degenerate 3Egθ state with a (dxy)2(dxz,yz)3(dz2)1/(dz2)2(dxy)1(dxz,yz)3 configuration. To address this question, we present herein a comprehensive, spectroscopy-based theoretical and experimental electronic-structure investigation on complex 1. Highly correlated wave-function-based computations predicted that 3A2g and 3Egθ are well-isolated from other triplet states by ca. 4000 cm-1, whereas their splitting ΔA-E is on par with the effective spin-orbit coupling (SOC) constant of iron(II) (≈400 cm-1). Therfore, we invoked an effective Hamiltonian (EH) operating on the nine magnetic sublevels arising from SOC between the 3A2g and 3Egθ states. This approach enabled us to successfully simulate all spectroscopic data of 1 obtained by variable-temperature and variable-field magnetization, applied-field 57Fe Mössbauer, and terahertz electron paramagnetic resonance measurements. Remarkably, the EH contains only three adjustable parameters, namely, the energy gap without SOC, ΔA-E, an angle θ that describes the mixing of (dxy)2(dxz,yz)3(dz2)1 and (dz2)2(dxy)1(dxz,yz)3 configurations, and the ⟨rd-3⟩ expectation value of the iron d orbitals that is necessary to estimate the 57Fe magnetic hyperfine coupling tensor. The EH simulations revealed that the triplet ground state of 1 is genuinely multiconfigurational with substantial parentages of both 3A2g (<88%) and 3Eg (>12%), owing to their accidental near-triple degeneracy with ΔA-E = +950 cm-1. As a consequence of this peculiar electronic structure, 1 exhibits a huge effective magnetic moment (4.2 μB at 300 K), large temperature-independent paramagnetism, a large and positive axial zero-field splitting, strong easy-plane magnetization (g⊥ ≈ 3 and g∥ ≈ 1.7) and a large and positive internal field at the 57Fe nucleus aligned in the xy plane. Further in-depth analyses suggested that g⊥ ≫ g∥ is a general spectroscopic signature of near-triple orbital degeneracy with more than half-filled pseudodegenerate orbital sets. Implications of the unusual electronic structure of 1 for CO2 reduction are discussed.
Collapse
Affiliation(s)
- Maxime Tarrago
- Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470 Mülheim an der Ruhr, Germany
| | - Christina Römelt
- Max-Planck-Institut für Chemische Energiekonversion, Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany
| | - Joscha Nehrkorn
- Max-Planck-Institut für Chemische Energiekonversion, Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany
| | - Alexander Schnegg
- Max-Planck-Institut für Chemische Energiekonversion, Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany
| | - Frank Neese
- Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470 Mülheim an der Ruhr, Germany
| | - Eckhard Bill
- Max-Planck-Institut für Chemische Energiekonversion, Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany
| | - Shengfa Ye
- Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470 Mülheim an der Ruhr, Germany.,State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
| |
Collapse
|
2
|
Govind C, Karunakaran V. Ultrafast Relaxation Dynamics of Photoexcited Heme Model Compounds: Observation of Multiple Electronic Spin States and Vibrational Cooling. J Phys Chem B 2017; 121:3111-3120. [DOI: 10.1021/acs.jpcb.7b01416] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Chinju Govind
- Photosciences
and Photonics Section, Chemical Sciences and Technology Division, CSIR-National Institute for Interdisciplinary Science and Technology, Thiruvananthapuram 695 019, Kerala India
- Academy of Scientific and Innovative Research (AcSIR), New Delhi 110 001, India
| | - Venugopal Karunakaran
- Photosciences
and Photonics Section, Chemical Sciences and Technology Division, CSIR-National Institute for Interdisciplinary Science and Technology, Thiruvananthapuram 695 019, Kerala India
- Academy of Scientific and Innovative Research (AcSIR), New Delhi 110 001, India
| |
Collapse
|
3
|
He M, Li X, Liu Y, Li J. Axial Mn–CCN Bonds of Cyano Manganese(II) Porphyrin Complexes: Flexible and Weak? Inorg Chem 2016; 55:5871-9. [PMID: 27228473 DOI: 10.1021/acs.inorgchem.6b00173] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Mingrui He
- College
of Materials Science and Optoelectronic Technology, University of Chinese Academy of Sciences, Yanqi Lake, Huairou District,
Beijing 101408, China
| | - Xiangjun Li
- College
of Materials Science and Optoelectronic Technology, University of Chinese Academy of Sciences, Yanqi Lake, Huairou District,
Beijing 101408, China
| | - Yanhong Liu
- Technical
Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China
| | - Jianfeng Li
- College
of Materials Science and Optoelectronic Technology, University of Chinese Academy of Sciences, Yanqi Lake, Huairou District,
Beijing 101408, China
| |
Collapse
|
4
|
Abstract
The synthesis of six new bis(cyano) iron(III) porphyrinate derivatives is reported. The anionic porphyrin complexes utilized tetraphenylporphyrin, tetramesitylporphyrin, and tetratolylporphyrin as the porphyrin ligand. The potassium salts of Kryptofix-222 and 18-C-6 were used as the cations. These complexes have been characterized by X-ray structure analysis, solid-state Mössbauer spectroscopy, and EPR spectroscopy, both in frozen CH2Cl2 solution and in the microcrystalline state. These data show that these anionic complexes can exist in either the (dxz,dyz)(4)(dxy)(1) or the (dxy)(2)(dxz,dyz)(3) electronic configuration and some can clearly readily interconvert. This is a reflection that these two states can be very close in energy. In addition to the effects of varying the porphyrin ligand, subtle effects of the cyanide ligand environment in the solid state and in solution are sufficient to shift the balance between the two electronic states.
Collapse
|
5
|
Moiseev AG, Margulies EA, Schneider JA, Bélanger-Gariépy F, Perepichka DF. Protecting the triplet excited state in sterically congested platinum porphyrin. Dalton Trans 2014; 43:2676-83. [DOI: 10.1039/c3dt52926f] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
6
|
Franke A, van Eldik R. Factors That Determine the Mechanism of NO Activation by Metal Complexes of Biological and Environmental Relevance. Eur J Inorg Chem 2012. [DOI: 10.1002/ejic.201201111] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
|
7
|
Nakamura M, Ikezaki A, Takahashi M. Metal-Porphyrin Orbital Interactions in Paramagnetic Iron Complexes Having Planar and Deformed Porphyrin Ring. J CHIN CHEM SOC-TAIP 2012. [DOI: 10.1002/jccs.201200474] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
|
8
|
Van Doorslaer S, Tilleman L, Verrept B, Desmet F, Maurelli S, Trandafir F, Moens L, Dewilde S. Marked difference in the electronic structure of cyanide-ligated ferric protoglobins and myoglobin due to heme ruffling. Inorg Chem 2012; 51:8834-41. [PMID: 22877248 DOI: 10.1021/ic3007074] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Electron paramagnetic resonance experiments reveal a significant difference between the principal g values (and hence ligand-field parameters) of the ferric cyanide-ligated form of different variants of the protoglobin of Methanosarcina acetivorans (MaPgb) and of horse heart myoglobin (hhMb). The largest principal g value of the ferric cyanide-ligated MaPgb variants is found to be significantly lower than for any of the other globins reported so far. This is at least partially caused by the strong heme distortions as proven by the determination of the hyperfine interaction of the heme nitrogens and mesoprotons. Furthermore, the experiments confirm recent theoretical predictions [Forti, F.; Boechi, L., Bikiel, D., Martí, M.A.; Nardini, M.; Bolognesi, M.; Viappiani, C.; Estrin, D.; Luque, F. J. J. Phys. Chem. B 2011, 115, 13771-13780] that Phe(G8)145 plays a crucial role in the ligand modulation in MaPgb. Finally, the influence of the N-terminal 20 amino-acid chain on the heme pocket in these protoglobins is also proven.
Collapse
|
9
|
Oszajca M, Franke A, Brindell M, Stochel G, van Eldik R. Mechanistic studies on the reactions of cyanide with a water-soluble Fe(III) porphyrin and their effect on the binding of NO. Inorg Chem 2011; 50:3413-24. [PMID: 21428315 DOI: 10.1021/ic1023345] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The reaction of the water-soluble Fe(III)(TMPS) porphyrin with CN(-) in basic solution leads to the stepwise formation of Fe(III)(TMPS)(CN)(H(2)O) and Fe(III)(TMPS)(CN)(2). The kinetics of the reaction of CN(-) with Fe(III)(TMPS)(CN)(H(2)O) was studied as a function of temperature and pressure. The positive value of the activation volume for the formation of Fe(III)(TMPS)(CN)(2) is consistent with the operation of a dissociatively activated mechanism and confirms the six-coordinate nature of the monocyano complex. A good agreement between the rate constants at pH 8 and 9 for the formation of the dicyano complex implies the presence of water in the axial position trans to coordinated cyanide in the monocyano complex and eliminates the existence of Fe(III)(TMPS)(CN)(OH) under the selected reaction conditions. Both Fe(III)(TMPS)(CN)(H(2)O) and Fe(III)(TMPS)(CN)(2) bind nitric oxide (NO) to form the same nitrosyl complex, namely, Fe(II)(TMPS)(CN)(NO(+)). Kinetic studies indicate that nitrosylation of Fe(III)(TMPS)(CN)(2) follows a limiting dissociative mechanism that is supported by the independence of the observed rate constant on [NO] at an appropriately high excess of NO, and the positive values of both the activation parameters ΔS(‡) and ΔV(‡) found for the reaction under such conditions. The relatively small first-order rate constant for NO binding, namely, (1.54 ± 0.01) × 10(-2) s(-1), correlates with the rate constant for CN(-) release from the Fe(III)(TMPS)(CN)(2) complex, namely, (1.3 ± 0.2) × 10(-2) s(-1) at 20 °C, and supports the proposed nitrosylation mechanism.
Collapse
Affiliation(s)
- Maria Oszajca
- Inorganic Chemistry, Department of Chemistry and Pharmacy, University of Erlangen-Nürnberg, Egerlandstrasse 1, 91058 Erlangen, Germany
| | | | | | | | | |
Collapse
|
10
|
Effects of hydrogen bonding interaction and solvent polarity on the competition between excitation energy and photo-induced electron transfer processes in hydroxy(1-pyrenebutoxy)phosphorus(V)porphyrin. J Photochem Photobiol A Chem 2010. [DOI: 10.1016/j.jphotochem.2010.05.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
|
11
|
Stuzhin PA, Nefedov SE, Kumeev RS, Ul-Haq A, Minin VV, Ivanova SS. Effects of Solvation on the Spin State of Iron(III) in 2,8,12,18-Tetrabutyl-3,7,13,17-tetramethyl-5,10-diazaporphyrinatoiron(III) Chloride. Inorg Chem 2010; 49:4802-13. [DOI: 10.1021/ic9012075] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Pavel A. Stuzhin
- Department of Organic Chemistry, Ivanovo State University of Chemical Technology, Friedrich Engels Pr-t, 7, RF-153000 Ivanovo, Russia
| | - Sergei E. Nefedov
- N. S. Kurnakov Institute of General and Inorganic Chemistry RAS, Leninskij Pr-t, 31, RF-119991 Moscow, Russia
| | - Roman S. Kumeev
- Institute of Solution Chemistry RAS, ul. Akademicheskaja, 1, RF-153045 Ivanovo, Russia
| | - Anwar Ul-Haq
- Department of Organic Chemistry, Ivanovo State University of Chemical Technology, Friedrich Engels Pr-t, 7, RF-153000 Ivanovo, Russia
| | - Vadim V. Minin
- N. S. Kurnakov Institute of General and Inorganic Chemistry RAS, Leninskij Pr-t, 31, RF-119991 Moscow, Russia
| | - Svetlana S. Ivanova
- Department of Organic Chemistry, Ivanovo State University of Chemical Technology, Friedrich Engels Pr-t, 7, RF-153000 Ivanovo, Russia
| |
Collapse
|
12
|
Li J, Noll BC, Schulz CE, Scheidt WR. Comparison of cyanide and carbon monoxide as ligands in iron(II) porphyrinates. Angew Chem Int Ed Engl 2009; 48:5010-3. [PMID: 19492380 DOI: 10.1002/anie.200901434] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Spot the difference: The five-coordinate iron(II) cyanoporphyrinates, which are spin-crossover compounds, can be used to synthesize previously unknown six-coordinate complexes. Bis(cyano) and (cyano)imidazole complexes are presented, and the five- and six-coordinate (cyano)iron(II) derivatives are compared with analogous CO complexes.
Collapse
Affiliation(s)
- Jianfeng Li
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, USA
| | | | | | | |
Collapse
|
13
|
Ikezaki A, Ohgo Y, Nakamura M. NMR studies on the electronic structure of one-electron oxidized complexes of iron(III) porphyrinates. Coord Chem Rev 2009. [DOI: 10.1016/j.ccr.2009.01.003] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
|
14
|
Li J, Noll B, Schulz C, Scheidt W. Comparison of Cyanide and Carbon Monoxide as Ligands in Iron(II) Porphyrinates. Angew Chem Int Ed Engl 2009. [DOI: 10.1002/ange.200901434] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
|
15
|
Patra R, Rath SP. Cyanide binding to iron in a highly distorted porphyrin macrocycle: Synthesis and structure of low-spin Fe(II) dicyano porphyrin. INORG CHEM COMMUN 2009. [DOI: 10.1016/j.inoche.2009.04.016] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
|
16
|
Li J, Lord RL, Noll BC, Baik MH, Schulz CE, Scheidt WR. Cyanide: a strong-field ligand for ferrohemes and hemoproteins? Angew Chem Int Ed Engl 2009; 47:10144-6. [PMID: 18989877 DOI: 10.1002/anie.200804116] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Jianfeng Li
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, USA
| | | | | | | | | | | |
Collapse
|
17
|
Li J, Lord R, Noll B, Baik MH, Schulz C, Scheidt W. Cyanide: A Strong-Field Ligand for Ferrohemes and Hemoproteins? Angew Chem Int Ed Engl 2008. [DOI: 10.1002/ange.200804116] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
|
18
|
Neya S, Takahashi A, Ode H, Hoshino T, Ikezaki A, Ohgo Y, Takahashi M, Furutani Y, Lórenz-Fonfría VA, Kandori H, Hiramatsu H, Kitagawa T, Teraoka J, Funasaki N, Nakamura M. Electronic Properties in a Five-Coordinate Azido Complex of Nonplanar Iron(III) Porphyrin: Revisiting to Quantum Mechanical Spin Admixing. BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 2008. [DOI: 10.1246/bcsj.81.136] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
|
19
|
Ikezaki A, Tukada H, Nakamura M. Control of electronic structure of a six-coordinate iron(iii) porphyrin radical by means of axial ligands. Chem Commun (Camb) 2008:2257-9. [DOI: 10.1039/b800674a] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
20
|
Moreira LM, Vieira dos Santos F, Lyon JP, Maftoum-Costa M, Pacheco-Soares C, Soares da Silva N. Photodynamic Therapy: Porphyrins and Phthalocyanines as Photosensitizers. Aust J Chem 2008. [DOI: 10.1071/ch08145] [Citation(s) in RCA: 155] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The present work is focussed on the principles of photodynamic therapy (PDT), emphasizing the photochemical mechanisms of reactive oxygen species formation and the consequent biochemical processes generated by the action of reactive oxygen species on various biological macromolecules and organelles. This paper also presents some of the most used photosensitizers, including Photofrin, and the new prototypes of photosensitizers, analysing their physicochemical and spectroscopic properties. At this point, the review discusses the therapeutic window of absorption of specific wavelengths involving first- and second-generation photosensitizers, as well as the principal light sources used in PDT. Additionally, the aggregation process, which consists in a phenomenon common to several photosensitizers, is studied. J-aggregates and H-aggregates are discussed, along with their spectroscopic effects. Most photosensitizers have a significant hydrophobic character; thus, the study of the types of aggregation in aqueous solvent is very relevant. Important aspects of the coordination chemistry of metalloporphyrins and metallophthalocyanines used as photosensitizers are also discussed. The state-of-the-art in PDT is evaluated, discussing recent articles in this area. Furthermore, macrocyclic photosensitizers, such as porphyrins and phthalocyanines, are specifically described. The present review is an important contribution, because PDT is one of the most auspicious advances in the therapy against cancer and other non-malignant diseases.
Collapse
|
21
|
Juillard S, Bondon A, Simonneaux G. Proton NMR Study of Low‐Spin
meso
‐Unsubstituted β‐Substituted Alkyl Iron Porphyrins: Remarkable Influence of Peripheral Substitution on Spin Density. Eur J Inorg Chem 2007. [DOI: 10.1002/ejic.200700503] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Sandrine Juillard
- Laboratoire de Chimie Organométallique et Biologique, UMR CNRS 6226 Campus de Beaulieu,Université de Rennes 1, 35042 Rennes, France
| | - Arnaud Bondon
- RMN‐ILP, UMR CNRS 6026, IFR 140 PRISM, Campus de Villejean, Université de Rennes 1, 35043 Rennes, France
| | - Gérard Simonneaux
- Laboratoire de Chimie Organométallique et Biologique, UMR CNRS 6226 Campus de Beaulieu,Université de Rennes 1, 35042 Rennes, France
| |
Collapse
|
22
|
Dürr K, Macpherson BP, Warratz R, Hampel F, Tuczek F, Helmreich M, Jux N, Ivanović-Burmazović I. Iron(III) Complex of a Crown Ether−Porphyrin Conjugate and Reversible Binding of Superoxide to Its Iron(II) Form. J Am Chem Soc 2007; 129:4217-28. [PMID: 17371019 DOI: 10.1021/ja064984p] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The synthesis and characterization of the Fe(III) complex of a novel crown ether-porphyrin conjugate, 52-N-(4-aza-18-crown-6)methyl-54,104,154,204-tetra-tert-butyl-56-methyl-5,10,15,20-tetraphenylporphyrin (H2Porph), as well as the corresponding hydroxo, dimeric, Fe(II), and peroxo species are reported. The crystal structure of [FeIII(Porph)Cl].H3O+.FeCl4-.C6H6.EtOH is also reported. [FeIII(Porph)(DMSO)2]+ and K[FeIII(Porph)(O22-)] are high-spin species (Mössbauer data: delta = 0.38 mm s(-1), DeltaEq = 0.83 mm s(-1) and delta = 0.41 mm s(-1), DeltaEq = 0.51 mm s(-1), respectively), whereas in a solution of reduced [FeIII(Porph)(DMSO)2]+ complex the low-spin [FeII(Porph)(DMSO)2] (delta = 0.44 mm s(-1), DeltaEq = 1.32 mm s(-1)) and high-spin [FeII(Porph)(DMSO)] (delta = 1.27 mm s(-1), DeltaEq = 3.13 mm s(-1)) iron(II) species are observed. The reaction of [FeIII(Porph)(DMSO)2]+ with KO2 in DMSO has been investigated. The first reaction step, involving reduction to [FeII(Porph)(DMSO)2], was not investigated in detail because of parallel formation of an Fe(III)-hydroxo species. The kinetics and thermodynamics of the second reaction step, reversible binding of superoxide to the Fe(II) complex and formation of an Fe(III)-peroxo species, were studied in detail (by stopped-flow time-resolved UV/vis measurements in DMSO at 25 degrees C), resulting in kon = 36 500 +/- 500 M(-1) s(-1), koff = 0.21 +/- 0.01 s(-1) (direct measurements using an acid as a superoxide scavenger), and KO2- = (1.7 +/- 0.2) x 10(5) (superoxide binding constant kinetically obtained as kon/koff), (1.4 +/- 0.1) x 10(5), and (9.0 +/- 0.1) x 10(4) M(-1) (thermodynamically obtained in the absence and in the presence of 0.1 M NBu4PF6, respectively). Temperature-dependent kinetic measurements for kon (-40 to 25 degrees C in 3:7 DMSO/CH3CN mixture) yielded the activation parameters DeltaH = 61.2 +/- 0.9 kJ mol(-1) and DeltaS = +48 +/- 3 J K(-1) mol(-1). The observed reversible binding of superoxide to the metal center and the obtained kinetic and thermodynamic parameters are unique. The finding that fine-tuning of the proton concentration can cause the Fe(III)-peroxo species to release O2- and form an Fe(II) species is of biological interest, since this process might occur under very specific physiological conditions.
Collapse
Affiliation(s)
- Katharina Dürr
- Institute of Inorganic Chemistry, University of Erlangen-Nürnberg, Egerlandstrasse 1, 91058 Erlangen, Germany
| | | | | | | | | | | | | | | |
Collapse
|
23
|
Li J, Noll BC, Schulz CE, Scheidt WR. New insights on the electronic and molecular structure of cyanide-ligated iron(III) porphyrinates. Inorg Chem 2007; 46:2286-98. [PMID: 17309249 PMCID: PMC2532704 DOI: 10.1021/ic061463u] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The preparation and characterization of several new cyano-ligated six-coordinate low-spin iron(III) porphyrinates are reported. The synthesis and structure of the new bis(cyanide) derivative K(222)][Fe(TMP)(CN)2] (TMP = tetramesitylporphyrinate) is described. Three mixed-ligand species of the general form [Fe(Porph)(CN)(L)], where L = 1-methylimidazole or pyridine, have also been prepared and structurally characterized. All complexes have been studied with EPR spectroscopy in frozen solution and in microcrystalline form. In some cases, especially those of the bis(cyanide) derivative above and the previously reported [Fe(TPP)(CN)2](-), there are significant differences in the EPR spectra as a result of the state change. These spectral differences can be correlated with changes in the electron configuration that are the likely result of a differing environment of the coordinated cyanide ligands; the core conformation and electronic structure of the porphyrin ligand are unlikely to play a role. All four new complexes and [Fe(TPP)(CN)2](-) have been studied by Mössbauer spectroscopy with variable-temperature and applied magnetic-field measurements. The sign of the quadrupole splitting value has been established as negative. These measurements have allowed us to give estimates of the energy difference between the two close-lying dpi (dxz and dyz) orbitals. These splitting values range from approximately 267 cm-1 for [Fe(TPP)(CN)2](-) to approximately 614 cm(-1) for [Fe(TPP)(CN)(Py)].
Collapse
Affiliation(s)
- Jianfeng Li
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, USA
| | | | | | | |
Collapse
|
24
|
|
25
|
Berlicka A, Latos-Grazyński L, Lis T. 1H NMR Investigation of High-Spin and Low-Spin Iron(III) meso-Ethynylporphyrins. Inorg Chem 2005; 44:4522-33. [PMID: 15962959 DOI: 10.1021/ic050158q] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The 1H NMR spectra of iron(III) 5-ethynyl-10,15,20-tri(p-tolyl)porphyrin [(ETrTP)Fe(III)X(n)], iron(III) 5-(phenylethynyl)-10,15,20-tri(p-tolyl)porphyrin [(PETrTP)Fe(III)X(n)], iron(III) 5-(phenylbutadiynyl)-10,15,20-tri(p-tolyl)porphyrin [(PBTrTP)Fe(III)X(n)], iron(III) 5,10,15,20-tetra(phenylethynyl)porphyrin [(TPEP)Fe(III)X(n)], iron(III) 1,4-bis-[10,15,20-tri(p-tolyl)porphyrin-5-yl]-1,3-butadiyne {[(TrTP)Fe(III)X(n)]2 B}, and 5,10,15-triphenylporphyrin [(TrPP)Fe(III)X(n)] have been studied to elucidate the impact of meso-ethynyl substitution on the electronic structure and spin density distribution of high-spin (X = Cl-, n = 1) and low-spin (X = CN-, n = 2) derivatives. The meso substituents, i.e., ethynyl, phenylethynyl, and phenylbutadiynyl, provided insight into the efficiency of spin density delocalization along structural elements that are typically applied to transmit electronic effects along multipart polyporphyrinic systems. The positive spin density localized at the meso-carbon of high-spin iron(III) ethynylporphyrins is effectively delocalized along the ethyne or butadiyne fragment as illustrated by the comparison of isotropic shifts of C(meso)-H and -CC-H determined for (TrPP)Fe(III)Cl (-82.6 ppm, 293 K) and (ETrTP)Fe(III)Cl (-49.5 ppm, 298 K). The replacement of the ethynyl hydrogen by phenyl or phenylethynyl provided evidence for the pi spin density distribution around the introduced phenyl ring. An analysis of the isotropic shifts for the low-spin bis-cyanide iron(III) porphyrins series reveals the analogous mechanism of spin density transfer. Treatment of high-spin [(TrTP)Fe(III)Cl]2 B with a base resulted in formation of the cyclic [(TrTP)Fe(III)OFe(III)(TrTP)B]2 complex linked by two mu-oxo bridges. (TPEP)H2 has been characterized by X-ray crystallography as a porphyrin dication where two molecules of trifluoroacetic acid associate with two coordinated trifluoroacetate anions. The X-ray structure of bis-tetrahydrofuran 1,4-bis[10,15,20-tri(p-tolyl)porphyrinatozinc(II)-5-yl]-1,3-butadiyne complex {[(TrTP)Zn(II)(THF)]2 B} reveals two parallel, non-coplanar [(TrTP)Zn(THF)] subunits linked by the linear butadiyne moiety.
Collapse
Affiliation(s)
- Anna Berlicka
- Department of Chemistry, University of Wrocław, 50 383 Wrocław, Poland
| | | | | |
Collapse
|