An iron(III) porphyrin that exhibits minimal dimerization in aqueous solution

Hambright, Peter; Turner, A.; Cohen, Jack S.; Lyon, Robbe C.; Katz, Arie; Neta, P.; Adeyemo, Adegboye

doi:10.1016/s0020-1693(00)84681-2

Cited by 9 publications

(3 citation statements)

References 32 publications

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“…Although the +2 oxidation state of manganese was proposed, the reported magnetic moment in chloroform of μ eff = 5.15 μ B 19 would suggest a +3 rather than a +2 oxidation state for manganese . Balch and co-workers have shown that Mn(III) and Fe(III) form dimers, while other metal ions such as Ni(II), Zn(II), Cu(II), and Co(II) exist as monomeric complexes. ,− Our magnetic moments in methanol and in the solid state, compared with those of known manganese compounds, , strongly support the +3 state in {Mn III BVDME} 2 55 and are in agreement with measurements on the related manganese(III) octaethylbilindione in chloroform …”

Section: Discussionsupporting

confidence: 83%

“…55 Balch and co-workers have shown that Mn(III) and Fe(III) form dimers, while other metal ions such as Ni(II), Zn(II), Cu(II), and Co(II) exist as monomeric complexes. 53,89-94 Our magnetic moments in methanol and in the solid state, compared with those of known manganese compounds, 95,96 strongly support the +3 state in {Mn III BVDME} 2 55 and are in agreement with measurements on the related manganese(III) octaethylbilindione in chloroform. 53 The two redox systems of {Mn III BVDME} 2 observed are assigned to metal-centered processes, since no electrochemistry of the biliverdin dimethyl ester was observed at such potentials.…”

Section: Discussionsupporting

confidence: 66%

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Manganese(III) Biliverdin IX Dimethyl Ester: A Powerful Catalytic Scavenger of Superoxide Employing the Mn(III)/Mn(IV) Redox Couple

et al. 2001

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A manganese(III) complex of biliverdin IX dimethyl ester, (MnIIIBVDME)2, was prepared and characterized by elemental analysis, UV/vis spectroscopy, cyclic voltammetry, chronocoulometry, electrospray mass spectrometry, freezing-point depression, magnetic susceptibility, and catalytic dismuting of superoxide anion (O2.-). In a dimeric conformation each trivalent manganese is bound to four pyrrolic nitrogens of one biliverdin dimethyl ester molecule and to the enolic oxygen of another molecule. This type of coordination stabilizes the +4 metal oxidation state, whereby the +3/+4 redox cycling of the manganese in aqueous medium was found to be at E1/2 = +0.45 V vs NHE. This potential allows the Mn(III)/Mn(IV) couple to efficiently catalyze the dismutation of O2.- with the catalytic rate constant of kcat = 5.0 x 10(7) M-1 s-1 (concentration calculated per manganese) obtained by cytochrome c assay at pH 7.8 and 25 degrees C. The fifth coordination site of the manganese is occupied by an enolic oxygen, which precludes binding of NO., thus enhancing the specificity of the metal center toward O2.-. For the same reason the (MnIIIBVDME)2 is resistant to attack by H2O2. The compound also proved to be an efficient SOD mimic in vivo, facilitating the aerobic growth of SOD-deficient Escherichia coli.

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Section: Discussionsupporting

confidence: 83%

Section: Discussionsupporting

confidence: 66%

Manganese(III) Biliverdin IX Dimethyl Ester: A Powerful Catalytic Scavenger of Superoxide Employing the Mn(III)/Mn(IV) Redox Couple

et al. 2001

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“…This observation is rationalized by the existence of four atropisomers of the TM2PyP ligand (due to inhibition of free rotation of the four N -methylpyridinium groups at the meso positions) . For porphyrins with more highly inhibited rotation, such as the tetrakis(2-( N -methylisonicotinamido)phenyl)porphyrin, where the four isomers could be separated, it has been shown that the p K a for protonation of the free bases varied between 2.2 and 2.9, and the rates of metal incorporation varied by an order of magnitude for the different isomers . Since decay of the Fe I TM2PyP is probably affected by protonation, it is likely that the different isomers will exhibit different decay behavior.…”

Section: Resultsmentioning

confidence: 99%

Iron Porphyrin-Catalyzed Reduction of CO₂. Photochemical and Radiation Chemical Studies

et al. 1997

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Several iron porphyrins have been reduced by photochemical and radiation chemical methods, in organic solvents and in aqueous solutions, from FeIIIP to FeIIP to FeIP and beyond. In aqueous solutions, the FeIP state is relatively stable for the tetrakis(N-methyl-2-pyridyl)porphyrin at high pH but is shorter lived in neutral and acidic solutions. The FeIP state of tetrakis(N-methyl-3-pyridyl)porphyrin and tetrakis(N-methyl-4-pyridyl)porphyrin are short-lived at any pH. Decay of FeIP is accelerated by H+ and by CO2, probably via reaction with the Fe0P state formed upon disproportionation of FeIP. These reactions may lead to formation of H2 and CO, respectively, and to formation of the chlorin, FeIIPH2, as a side product. The FeIP state is also observed as a stable product in several organic solvents. This is observed by photolysis of iron tetraphenylporphyrin and several of its derivatives (e.g., trimethyl-, dichloro- and pentafluorophenyl), mainly in dimethylformamide and acetonitrile solutions, using triethylamine as a reductive quencher. Further photoreduction in the presence of CO2 results in catalyzed reduction of CO2 to CO and formation of (CO)FeIIP. The yield of free CO increases with time of photolysis and reaches turnover numbers of ∼70 molecules of CO per porphyrin molecule.

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Iron Porphyrin Chemistry

Walker¹,

Simonis²

2005

Encyclopedia of Inorganic Chemistry

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This article reviews most aspects of the chemistry of iron porphyrins, from Fe(0) to Fe(V), including occurrence and roles of natural iron porphyrins (hemes) and their synthetic analogs, structures and electron configurations of iron porphyrins of all oxidation and spin states, π electron configuration of the porphyrin ring, synthesis of metal‐free porphyrins and other related macrocycles, insertion of iron into free‐base porphyrins and related macrocycles, the properties, reactions, uses and biological relevance of iron(0), ‐(I), ‐(II) porphyrins (the latter with S = 0, 1, and 2 spin state possibilities), of iron(II) porphyrin π‐cation radicals, of iron(III) porphyrins (with S = 1/2, 3/2, and 5/2 spin state possibilities), of iron(III) porphyrin and corrole π‐cation radicals, of iron(IV) porphyrins (including five‐ and six‐coordinate ferryl (FeO) 2+ , iron(IV) phenyl, carbene and hydrazine complexes, and the bis‐methoxide complex) and a comparison of iron(IV) porphyrins to iron(III) porphyrin π‐cation radicals, of iron(IV) porphyrin π‐cation radicals, and of the possible existence of iron(V) porphyrins. Included in the Fe(II) part are sections on addition of ligands to four‐coordinate iron(II) porphyrins, including equilibrium binding constants, photodissociation of ligands from PFeL 2 complexes, binding of small molecules (O 2 , CO, NO, HNO) to 5‐coordinate iron(II) porphyrins and design of porphyrin ligands that will mimic the active sites of heme proteins such as myoglobin and hemoglobin, the cytochromes P450 and nitric oxide synthases, and the nitrophorins and guanylyl cyclases. Included in the iron(III) part are sections on both 5‐ and 6‐coordinate high‐spin complexes and their similarities and differences, bridged or through‐space magnetically coupled complexes of high‐spin iron(III) porphyrins with other metal complexes as possible models for cytochrome oxidase and the assimilatory sulfite reductases, coupled oxidation of hemes by hydrogen peroxide or its equivalent, and the relationship of this reactivity to the reactions of heme oxygenase, iron(III) porphyrins as reduction catalysts, and photochemistry of iron(III) porphyrins, possible electron configurations of low‐spin iron(III) porphyrins, the phenomenon and possible electronic consequences of ruffling of the porphinato core in iron(III) porphyrins, the preferred orientation of planar axial ligands bound to low‐spin iron(III) porphyrins, NO complexes of iron(III) porphyrins, reduction potentials, equilibrium constants and rates of axial‐ligand addition and exchange, kinetics of axial‐ligand rotation and porphyrin ring inversion, kinetics of reduction and autoreduction of iron(III) porphyrins, electron self‐exchange between low‐spin iron(III) and iron(II) porphyrins, synthetic ferriheme proteins, and synthesis of five‐coordinate low‐spin iron(III) porphyrins having σ‐alkyl or σ‐aryl groups as axial ligands. The iron(IV) and iron(IV) cation radical sections discuss the high‐valent states of cytochromes P450 and related enzymes.

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An iron(III) porphyrin that exhibits minimal dimerization in aqueous solution

Cited by 9 publications

References 32 publications

Manganese(III) Biliverdin IX Dimethyl Ester: A Powerful Catalytic Scavenger of Superoxide Employing the Mn(III)/Mn(IV) Redox Couple

Manganese(III) Biliverdin IX Dimethyl Ester: A Powerful Catalytic Scavenger of Superoxide Employing the Mn(III)/Mn(IV) Redox Couple

Iron Porphyrin-Catalyzed Reduction of CO₂. Photochemical and Radiation Chemical Studies

Iron Porphyrin Chemistry

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An iron(III) porphyrin that exhibits minimal dimerization in aqueous solution

Cited by 9 publications

References 32 publications

Manganese(III) Biliverdin IX Dimethyl Ester: A Powerful Catalytic Scavenger of Superoxide Employing the Mn(III)/Mn(IV) Redox Couple

Manganese(III) Biliverdin IX Dimethyl Ester: A Powerful Catalytic Scavenger of Superoxide Employing the Mn(III)/Mn(IV) Redox Couple

Iron Porphyrin-Catalyzed Reduction of CO2. Photochemical and Radiation Chemical Studies

Iron Porphyrin Chemistry

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Iron Porphyrin-Catalyzed Reduction of CO₂. Photochemical and Radiation Chemical Studies