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A Hybrid Density Functional Study of O-O Bond Cleavage and Phenyl Ring Hydroxylation for a Biomimetic Non-Heme Iron Complex
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics.
2004 (English)In: Inorganic Chemistry, ISSN 0020-1669, Vol. 43, no 10, 3277-3291 p.Article in journal (Refereed) Published
Abstract [en]

Density functional calculations using the B3LYP functional have been used to study the reaction mechanism of [Fe(TpPh2)BF] (TpPh2 = hydrotris(3,5-diphenylpyrazol-1-yl)borate; BF = benzoylformate) with dioxygen. This mononuclear non-heme iron(II) complex was recently synthesized, and it proved to be the first biomimetic complex reproducing the dioxygenase activity of α-ketoglutarate-dependent enzymes. Moreover, the enthalpy and entropy of activation for this biologically interesting process were derived from kinetic experiments offering a unique possibility for direct comparison of theoretical and experimental data. The results reported here support a mechanism in which oxidative decarboxylation of the keto acid is the rate-limiting step. This oxygen activation process proceeds on the septet potential energy surface through a transition state for a concerted O−O and C−C bond cleavage. In the next step, a high-valent iron−oxo species performs electrophilic attack on the phenyl ring of the TpPh2 ligand leading to an iron(III)−radical σ-complex. Subsequent proton-coupled electron-transfer yields an iron(II)−phenol intermediate, which can bind dioxygen and reduce it to a superoxide radical. Finally, the protonated superoxide radical leaves the first coordination sphere of the iron(III)−phenolate complex and dismutates to dioxygen and hydrogen peroxide. The calculated activation barrier (enthalpy and entropy) and the overall reaction energy profile agree well with experimental data. A comparison to the enzymatic process, which is suggested to occur on the quintet surface, has been made.

Place, publisher, year, edition, pages
2004. Vol. 43, no 10, 3277-3291 p.
URN: urn:nbn:se:su:diva-22677DOI: 10.1021/ic035395cOAI: diva2:189253
Part of urn:nbn:se:su:diva-103Available from: 2004-04-15 Created: 2004-04-15 Last updated: 2010-01-18Bibliographically approved
In thesis
1. Theoretical studies of mononuclear non-heme iron active sites
Open this publication in new window or tab >>Theoretical studies of mononuclear non-heme iron active sites
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The quantum chemical investigations presented in this thesis use hybrid density functional theory to shed light on the catalytic mechanisms of mononuclear non-heme iron oxygenases, accommodating a ferrous ion in their active sites. More specifically, the dioxygen activation process and the subsequent oxidative reactions in the following enzymes were studied: tetrahydrobiopterin-dependent hydroxylases, naphthalene 1,2-dioxygenase and α-ketoglutarate-dependent enzymes. In light of many experimental efforts devoted to the functional mimics of non-heme iron oxygenases, the reactivity of functional analogues was also examined.

The computed energetics and the available experimental data served to assess the feasibility of the reaction mechanisms investigated. Dioxygen activation in tetrahydrobiopterin- and α-ketoglutarate-dependent enzymes were found to involve a high-valent iron-oxo species, which was then capable of substrate hydroxylation. In the case of naphthalene 1,2-dioxygenase, the reactivity of an iron(III)-hydroxperoxo species toward the substrate was investigated and compared to the biomimetic counterpart.

Place, publisher, year, edition, pages
Stockholm: Fysikum, 2004. 86 p.
quantum chemistry, enzyme catalysis, iron enzymes
National Category
Theoretical Chemistry
urn:nbn:se:su:diva-103 (URN)91-7265-857-6 (ISBN)
Public defence
2004-05-07, sal FA32, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00
Available from: 2004-04-15 Created: 2004-04-15Bibliographically approved

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