Photo-decarboxylation of iron(III) porphyrin–amino acid complexes in aqueous solution

Gilbert, Bruce C.; Smith, John R. Lindsay; Parsons, Andrew F.; Setchell, Peter K.

doi:10.1039/a700251c

Cited by 18 publications

(13 citation statements)

References 31 publications

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“…An alternative proposal is that the reducing equivalents come from oxidation of axial ligands bound to the high‐spin heme a 3 (30,31) or proton channel water molecules (30). Axial ligand oxidation has been shown to occur in several model heme systems (65,66).…”

Section: Resultsmentioning

confidence: 99%

Photoreactions of Cytochrome c Oxidase

Winterle

Einarsdóttir

2006

Photochem & Photobiology

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The photoreduction of oxidized bovine heart cytochrome c oxidase (CcO) by visible and UV radiation was investigated in the absence and presence of external reagents. In the former case, the quantum yields for direct photoreduction of heme A (heme a + heme a(3)) were 2.6 +/- 0.5 x 10(-3), 4 +/- 1 x 10(-4), and 4 +/- 2 x 10(-6) with pulsed laser irradiation at 266, 355 and 532 nm, respectively. Within experimental uncertainty, the quantum yields did not depend on pulse energy, implying that the mechanism is monophotonic. Irradiation with 355 nm light resulted in spectral changes similar to those produced independently by reduction with dithionite, whereby the low-spin heme a and Cu(A) are reduced first. Extended illumination at 355 and 532 nm yielded substantial amounts of reduced heme a(3). Heme decomposition was noted with 266 nm light. In the presence of formate and cyanide ions, which bind at the binuclear heme a(3)/copper center in CcO, irradiation at 355 nm caused selective reduction of only the low-spin heme a and Cu(A). The addition of ferrioxalate ion dramatically increased the efficiency of cytochrome c oxidase photoreduction. The quantum efficiency for heme A reduction was found to be near unity, significantly greater than for other known methods of photoreduction. The active reductant is most likely ferrous iron, and its reduction of the enzyme is thermodynamically driven by the reformation of ferrioxalate in the presence of excess oxalate ion. Other metalloenzymes with redox potentials similar to those of cytochrome c oxidase should be amenable to indirect photoreduction by this method.

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Section: Resultsmentioning

confidence: 99%

Photoreactions of Cytochrome c Oxidase

Winterle

Einarsdóttir

2006

Photochem & Photobiology

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“…The first study of metalloporphyrin Langmuir-Blodgett films as catalysts for alkene oxidation was performed using the amphipathic FeTTD2PyPCl 5 [20]. Aqueous photocatalytic systems based on [FeTM2PyP] 5+ have also been successfully developed by Lindsay-Smith and coworkers [22][23][24] for the decarboxylation of amino and carboxylic acids.…”

Section: Introductionmentioning

confidence: 98%

“…1) has recently been established as a potentially useful porphyrin for the design of biomimetic catalysts [17][18][19][20][21][22][23][24][25][26][27][28]. Unlike their structural isomers (H 2 T4PyP or H 2 T3PyP), H 2 T2PyP derivatives can simultaneously combine pronounced steric and electronic effects, which are the essence of the design and reactivity control of both P450 model compounds and superoxide dismutase (SOD) mimics [28].…”

Section: Introductionmentioning

confidence: 99%

Perhalogenated 2-pyridylporphyrin complexes: synthesis, self-coordinating aggregation properties, and catalytic studies

Rebouças

Carvalho

Idemori

2002

J. Porphyrins Phthalocyanines

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The synthesis of 2, 3, 7, 8, 12, 13, 17, 18-octabromo-meso-tetrakis(2-pyridyl)porphyrin, H 2 Br 8 T2PyP, is described, including the comparison of four attempted methods for the demetallation of ZnBr 8 T2PyP. One of the methods represents a strategy of demetallation based on the acid-base properties of the macrocycle, the solvent-dependent kinetics of metal insertion into porphyrins and the pH-dependent solubility of the 2-pyridylporphyrin derivatives in water. Self-coordinating aggregation of ZnBr 8 T2PyP in non-coordinating solvents was verified by 1 H NMR spectroscopy. The Mn(III)/Mn(II) redox potential for MnBr 8 T2PyPCl is 0.38 V higher than the reduction potential measured for its first-generation analogue, MnT2PyPCl. Cyclohexane hydroxylation by iodosylbenzene was performed in CH 3 CN catalyzed by MnBr 8 T2PyPCl and MnT2PyPCl. MnBr 8 T2PyPCl was highly active, even at low concentration (5 x 10 -5 M), but perhalogenation did not account for oxidative robustness. At such a low catalyst concentration, MnT2PyPCl exhibited no activity as inferred by comparison to blank experiments.

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“…These and related issues prompted us to examine iron(III) and copper(II) salts as reagents and potential catalysts for photochemical conversion of carboxylic acids to hydrocarbons and functionalized derivatives. Metal ion-assisted decarboxylation, especially with iron compounds, has already received some attention, [26][27][28][29] but work with copper has been quite limited. 29,30 Several groups demonstrated increased photoreactivity of carboxylic acids in the presence of iron(III).…”

Section: Introductionmentioning

confidence: 99%

“…In the proposed mechanism, the photochemical cleavage of carboxylato iron complexes generates carboxyalkyl radicals followed by rapid thermal decarboxylation. 26,27,29 This conclusion was recently questioned in a study of Fe(III)-assisted decarboxylation of glyoxalic, tartaric, pyruvic, and lactic acids by Glebov et al 31 These authors invoked a persistent radical complex [Fe II ⋯˙OC (O)R] that dissociates into R(O)CO˙and Fe(II) on a millisecond time scale.…”

Section: Introductionmentioning

confidence: 99%

Transition metal ion-assisted photochemical generation of alkyl halides and hydrocarbons from carboxylic acids

2012

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Near-UV photolysis of aqueous solutions of propionic acid and aqueous Fe(3+) in the absence of oxygen generates a mixture of hydrocarbons (ethane, ethylene and butane), carbon dioxide, and Fe(2+). The reaction becomes mildly catalytic (about five turnovers) in the presence of oxygen which converts a portion of alkyl radicals to oxidizing intermediates that reoxidize Fe(2+). The photochemistry in the presence of halide ions (X(-) = Cl(-), Br(-)) generates ethyl halides via halogen atom abstraction from FeX(n)(3-n) by ethyl radicals. Near-quantitative yields of C(2)H(5)X are obtained at ≥0.05 M X(-). Competition experiments with Co(NH(3))(5)Br(2+) provided kinetic data for the reaction of ethyl radicals with FeCl(2+) (k = (4.0 ± 0.5) × 10(6) M(-1) s(-1)) and with FeBr(2+) (k = (3.0 ± 0.5) × 10(7) M(-1) s(-1)). Photochemical decarboxylation of propionic acid in the presence of Cu(2+) generates ethylene and Cu(+). Longer-chain acids also yield alpha olefins as exclusive products. These reactions become catalytic under constant purge with oxygen which plays a dual role. It reoxidizes Cu(+) to Cu(2+), and removes gaseous olefins to prevent accumulation of Cu(+)(olefin) complexes and depletion of Cu(2+). The results underscore the profound effect that the choice of metal ions, the medium, and reaction conditions exert on the photochemistry of carboxylic acids.

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Photo-decarboxylation of iron(III) porphyrin–amino acid complexes in aqueous solution

Cited by 18 publications

References 31 publications

Photoreactions of Cytochrome c Oxidase

Photoreactions of Cytochrome c Oxidase

Perhalogenated 2-pyridylporphyrin complexes: synthesis, self-coordinating aggregation properties, and catalytic studies

Transition metal ion-assisted photochemical generation of alkyl halides and hydrocarbons from carboxylic acids

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