Effect of the Axial Ligand on Substrate Sulfoxidation Mediated by Iron(IV)–Oxo Porphyrin Cation Radical Oxidants

2011 ◽  
Vol 17 (22) ◽  
pp. 6196-6205 ◽  
Author(s):  
Devesh Kumar ◽  
G. Narahari Sastry ◽  
Sam P. de Visser
Keyword(s):  
Cation Radical ◽  
Axial Ligand ◽  
Porphyrin Cation

Methane Hydroxylation by Axially Ligated Iron (IV)-oxo Porphyrin Cation Radical Models

2016 ◽  
Vol 1 (2) ◽  
Author(s):  
Devendra Singh ◽  
Devesh Kumar ◽  
Sam P. de Visser
Keyword(s):  
Hydrogen Atom ◽  
Cytochromes P450 ◽  
Cation Radical ◽  
Axial Ligand ◽  
Hydrogen Atom Abstraction ◽  
Energy Splitting ◽  
Compound I ◽  
Model Complexes ◽  
Mononuclear Iron ◽  
Porphyrin Cation

Methane hydroxylation is a thermochemically difficult process due to the strength of the C-H bond that needs to be broken in the process. In Nature only the methane monoxygenases have a catalytic center that is active enough to perform this task. Other metalloenzymes, such as, mononuclear iron monoxygenases and dioxygenases, including the cytochromes P450, are not known to catalyze methane hydroxylation. The cytochromes P450 contain an iron heme group that in a catalytic cycle is converted into an iron(IV)-oxo heme cation radical (Compound I). To gain insight into the features that affect methane hydroxylation by Compound I and synthetic model complexes, we have done a detailed computational study. Thus, we investigated the chemical properties of iron(IV)-oxo porphyrins with varying axial ligands, including SH<sup>−</sup>, F<sup>−</sup>, OH<sup>−</sup>, CN<sup>−</sup>, CF<sub>3</sub>COO<sup>−</sup> and CH<sub>3</sub>COO<sup>−</sup>. In addition, we calculated the methane hydroxylation pathways for a selection of these oxidants and rationalize the obtained trends with thermochemical cycles and valence bond schemes. In general, the rate determining hydrogen atom abstraction barrier is dependent on the π<sub>xz</sub>/π*<sub>xz</sub> energy splitting along the Fe−O bond, the excitation energy from π<sub>xz</sub> to a<sub>2u</sub>, as well as the bond dissociation energies of the methane C−H bond and the newly formed O−H bond. Our studies predict that iron(IV)-oxo porphyrin cation radical models with hydroxide as axial ligand should be efficient oxidants of substrate hydroxylation reactions and able to activate methane at room temperature. However, changing the axial ligand to a weaker electron donating group decreases its activity and raises the hydrogen atom abstraction barriers dramatically. These studies show that subtle modifications to the oxidant can have a great impact on the catalytic ability of the active center.

Triplet ESR spectrum of the copper porphyrin cation radical

1982 ◽  
Vol 104 (7) ◽  
pp. 2057-2059 ◽  
Author(s):  
S. Konishi ◽  
M. Hoshino ◽  
M. Imamura
Keyword(s):  
Cation Radical ◽  
Esr Spectrum ◽  
Copper Porphyrin ◽  
Porphyrin Cation

Effect of the Axial Ligand on the Reactivity of the Oxoiron(IV) Porphyrin π-Cation Radical Complex: Higher Stabilization of the Product State Relative to the Reactant State

2012 ◽  
Vol 51 (13) ◽  
pp. 7296-7305 ◽  
Author(s):  
Akihiro Takahashi ◽  
Daisuke Yamaki ◽  
Kenichiro Ikemura ◽  
Takuya Kurahashi ◽  
Takashi Ogura ◽  
...  
Keyword(s):  
Cation Radical ◽  
Axial Ligand ◽  
Product State ◽  
Radical Complex

scholarly journals A comprehensive test set of epoxidation rate constants for iron(iv)–oxo porphyrin cation radical complexes

2015 ◽  
Vol 6 (2) ◽  
pp. 1516-1529 ◽  
Author(s):  
Mala A. Sainna ◽  
Suresh Kumar ◽  
Devesh Kumar ◽  
Simonetta Fornarini ◽  
Maria Elisa Crestoni ◽  
...  
Keyword(s):  
Oxygen Atom ◽  
Gas Phase ◽  
Cation Radical ◽  
Compound I ◽  
Oxygen Atom Transfer ◽  
Test Set ◽  
Extensive Test ◽  
Comprehensive Test ◽  
First Time ◽  
Porphyrin Cation

Trends in oxygen atom transfer to Compound I of the P450 models with an extensive test set have been studied and show a preferred regioselectivity of epoxidation over hydroxylation in the gas-phase for the first time.

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