Optical absorption and EPR studies on a six-coordinate iron(<scp>III</scp>)–tetramesitylporphyrin–hydrogen peroxide complex having a nitrogenous axial ligand

Tajima, Kunihiko; Oka, Saori; Edo, Takeshi; Miyake, Shingo; Mano, Hirotsugu; Mukai, Kazuo; Sakuraï, H.; Ishizu, Kazuhiko

doi:10.1039/c39950001507

Cited by 37 publications

(41 citation statements)

References 12 publications

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“…(9); (---) kinetic rate for 5-hydroxycamphor formation, k ) 0.0035 s -1 ; (---) kinetic rate for autooxidation of putidaredoxin, k ) 0.007 s -1 (Sligar et al, 1974); (s) kinetic rate for 1.0 equiv of oxidized putidaredoxin formed in 1 s and 1.1 equiv autooxidize at the same rate above, k ) 0.007 s -1 . Coon, 1981;Davydov et al, 1991;Kappl et al, 1985;Nyman & Debrunner, 1991;Tajima et al, 1993) and observed model compounds (Balch, 1992;Tajima et al, 1995;Yamaguchi et al, 1993). The spectral intermediate observed with D251N is distinct from these species in both its UV-visible spectra and EPR spectra (Balch, 1992;Blake & Coon, 1981;Davydov et al, 1991;Kappl et al, 1985;Nyman & Debrunner, 1991;Tajima et al, 1993Tajima et al, , 1995Yamaguchi et al, 1993), suggesting the rate-determining step is the first proton transfer (5A and B to 5C).…”

Section: Resultsmentioning

confidence: 99%

“…This argues that the new intermediate precedes O-O bond heterolysis (5C to 6) since O-O bond heterolysis must also occur in peroxide-supported catalysis (Tajima et al, 1993;Egawa et al, 1994;Ortiz de Montellano, 1995b). In the hydrogen peroxide and alkylhydroperoxide supported catalysis, a ferric hydroperoxo (5C) or similar ferric alkylperoxo intermediates are proposed to be formed under nonphysiological conditions (Balch, 1992;Blake & Coon, 1981;Tajima et al, 1993Tajima et al, , 1995Yamaguchi et al, 1993). EPR and UV-visible signals for ferric hydroperoxo intermediates are well established from a variety of nonphysiological protein-based intermediates (Blake & 2 If the rate-determining step was the second electron transfer (4 to 5A-B), the kinetics of oxidized Pd formation would be expected to be a mixture of the rate of 5-hydroxycamphor formation (---in Figure 5) and autooxidation of excess reduced Pd (---in Figure 5).…”

Section: Resultsmentioning

confidence: 99%

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Reduced Oxy Intermediate Observed in D251N Cytochrome P450_cam

1997

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Cytochrome P450s are ubiquitous heme proteins responsible for various oxidative metabolic processes. The overall rate-determining step in the catalytic cycle of native cytochrome P450 cam is the reduction of the dioxygen complex, which has made detection of catalytic intermediates after this reduction impossible. However, for the site-specific mutant D251N cytochrome P450 cam (which affects proton transfer near the catalytic center), the overall rate-determining step occurs after the reduction of oxy-P450. As a consequence, we have observed in the UV-visible spectrum during catalytic turnover a new intermediate that is one electron reduced from oxy-P450 with an intact dioxygen bond.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Reduced Oxy Intermediate Observed in D251N Cytochrome P450_cam

1997

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“…9 It also exhibited an EPR spectrum (77 K) indicative of a low-spin ferric complex with anomalously small g anisotropy. The peroxide complexes Fe 3+ -OEP(OOH) 212 and Fe 3+ "TMP(OOH) 213 were also reported. The EPR spectra of these peroxide complexes contrasted with those of the high-spin ferric peroxo porphyrin complexes discussed earlier and were consistent with those of Fe m (hemoglobin)(OOH) and Fe'"(horseradish peroxidase)(OOH).…”

Section: Heme and Pseudo-heme Iron Dioxygen Complexesmentioning

confidence: 92%

Biomimetic Oxygenations Related to Cytochrome P450: Metal-Oxo and Metal-Peroxo Intermediates

McLain

Lee

Groves

2000

Biomimetic Oxidations Catalyzed by Transition Metal Complexes

123

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Oxometalloporphyrin Intermediates in Enzymatic ProcessesMetalloenzymes catalyze a host of biological oxidation reactions that are crucial to life processes. The cytochromes P450, an important family of heme-iron metalloenzymes, are oxidoreductases that activate molecular oxygen (O2) and incorporate one of the oxygen atoms into a wide variety of biological substrates, with concurrent two-electron reduction of the other oxygen atom to H 2 0.' The structure, biochemistry, molecular biology and the chemistry of cytochrome P450 and related model systems was extensively reviewed recently. 1 Cytochrome P450 enzymes have been isolated from numerous mammalian tissues (e.g. liver, kidney, lung, intestine and adrenal cortex), as well as insects, plants, yeast and bacteria, 2 and are known to catalyze hydroxylations, epoxidations, N-, S-and O-dealkylations, N-oxidations, sulfoxidations, and dehalogenations. 1 These oxygenation reactions play a central role in carcinogen activation, drug and xenobiotic detoxification, and steroid and prostaglandin metabolism. Surprisingly, the active site of the enzyme, known in detail from several X-ray crystal structures, is extraordinarily simple, with an iron protoporphyrin IX (3.1; Fig. 3.1) buried deep in a hydrophobic, substrate-binding pocket of 91 Biomimetic Oxidations Catalyzed by Transition Metal Complexes Downloaded from www.worldscientific.com by KAINAN UNIVERSITY on 02/20/15. For personal use only.

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“…Axial ligand exchange was also demonstrated in the case of complex 20 ( Figure 8), which was prepared by the addition of imidazole to a solution of the hydroxide precursor [59].…”

Section: Fe(iii)-hydroperoxo (Alkylperoxo) Intermediatesmentioning

confidence: 97%

Transition Metal Complexes and the Activation of Dioxygen

Yee

Tolman

2014

Metal Ions in Life Sciences

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In order to address how diverse metalloprotein active sites, in particular those containing iron and copper, guide O₂binding and activation processes to perform diverse functions, studies of synthetic models of the active sites have been performed. These studies have led to deep, fundamental chemical insights into how O₂coordinates to mono- and multinuclear Fe and Cu centers and is reduced to superoxo, peroxo, hydroperoxo, and, after O-O bond scission, oxo species relevant to proposed intermediates in catalysis. Recent advances in understanding the various factors that influence the course of O₂activation by Fe and Cu complexes are surveyed, with an emphasis on evaluating the structure, bonding, and reactivity of intermediates involved. The discussion is guided by an overarching mechanistic paradigm, with differences in detail due to the involvement of disparate metal ions, nuclearities, geometries, and supporting ligands providing a rich tapestry of reaction pathways by which O₂is activated at Fe and Cu sites.

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Optical absorption and EPR studies on a six-coordinate iron(III)–tetramesitylporphyrin–hydrogen peroxide complex having a nitrogenous axial ligand

Abstract: The formation of a six-coordinate FeiiiTMP-hydrogen peroxide complex (TMP = tetramesitylporphyrin), having a nitrogenous ligand at the axial position, is demonstrated by means of simultaneous EPR and optical absorption measurements a t 77 K.

Cited by 37 publications

References 12 publications

Reduced Oxy Intermediate Observed in D251N Cytochrome P450_cam

Reduced Oxy Intermediate Observed in D251N Cytochrome P450_cam

Biomimetic Oxygenations Related to Cytochrome P450: Metal-Oxo and Metal-Peroxo Intermediates

Transition Metal Complexes and the Activation of Dioxygen

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Optical absorption and EPR studies on a six-coordinate iron(III)–tetramesitylporphyrin–hydrogen peroxide complex having a nitrogenous axial ligand

Abstract: The formation of a six-coordinate FeiiiTMP-hydrogen peroxide complex (TMP = tetramesitylporphyrin), having a nitrogenous ligand at the axial position, is demonstrated by means of simultaneous EPR and optical absorption measurements a t 77 K.

Cited by 37 publications

References 12 publications

Reduced Oxy Intermediate Observed in D251N Cytochrome P450cam

Reduced Oxy Intermediate Observed in D251N Cytochrome P450cam

Biomimetic Oxygenations Related to Cytochrome P450: Metal-Oxo and Metal-Peroxo Intermediates

Transition Metal Complexes and the Activation of Dioxygen

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Product

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Reduced Oxy Intermediate Observed in D251N Cytochrome P450_cam

Reduced Oxy Intermediate Observed in D251N Cytochrome P450_cam