492 research outputs found
CCDC 1035749: Experimental Crystal Structure Determination
No full textRelated Article: Dipankar Sahoo, Matthew G. Quesne, Sam P. de Visser, Sankar Prasad Rath|2015|Angew.Chem.,Int.Ed.|54|4796|doi:10.1002/anie.20141139
CCDC 1035747: Experimental Crystal Structure Determination
No full textRelated Article: Dipankar Sahoo, Matthew G. Quesne, Sam P. de Visser, Sankar Prasad Rath|2015|Angew.Chem.,Int.Ed.|54|4796|doi:10.1002/anie.20141139
CCDC 1035748: Experimental Crystal Structure Determination
No full textRelated Article: Dipankar Sahoo, Matthew G. Quesne, Sam P. de Visser, Sankar Prasad Rath|2015|Angew.Chem.,Int.Ed.|54|4796|doi:10.1002/anie.20141139
Hydrogen atom versus hydride transfer in cytochrome P450 oxidations: A combined mass spectrometry and computational study
Get PDFBiomimetic models of short-lived enzymatic reaction intermediates can give useful insight into the properties and coordination chemistry of transition metal complexes. In this work we investigate a high-valent iron(IV)-oxo porphyrin cation radical complex, namely [FeIV(O)(TPFPP+*)]+ where TPFPP is the dianion of 5,10,15,20-tetrakis(pentafluorophenyl) porphyrin. The [FeIV(O)(TPFPP+*)]+ ion was studied by ion-molecule reactions in a Fourier transform-ion cyclotron resonance mass spectrometer through reactivities with 1,3,5-cycloheptatriene, 1,3-cyclohexadiene and toluene. The different substrates give dramatic changes in reaction mechanism and efficiencies, whereby cycloheptatriene leads to hydride transfer, while cyclohexadiene and toluene react via hydrogen atom abstraction. Detailed computational studies point to major differences in ionization energy as well as C-H bond energies of the substrates that influence the hydrogen atom abstraction versus electron transfer pathways. The various variables that determine the pathways for hydride transfer versus hydrogen atom transfer are elucidated and discussed
CCDC 1035750: Experimental Crystal Structure Determination
No full textRelated Article: Dipankar Sahoo, Matthew G. Quesne, Sam P. de Visser, Sankar Prasad Rath|2015|Angew.Chem.,Int.Ed.|54|4796|doi:10.1002/anie.20141139
Preferential Hydroxylation over Epoxidation Catalysis by a Horseradish Peroxidase Mutant: A Cytochrome P450 Mimic
No full textDensity functional theory calculations are presented on the catalytic properties of a horseradish peroxidase
mutant whereby the axial nitrogen atom is replaced by phosphorus. This mutant has never been studied
experimentally and only one theoretical report on this system is known (de Visser, S. P. J. Phys. Chem. B
2006, 110, 20759−20761). Thus, a one-atom substitution in horseradish peroxidase changes the properties of
the catalytic center of the enzyme to more cytochrome P450-type qualities. In particular, the phosphorus-substituted horseradish peroxidase mutant reacts with substrates via a unique reactivity pattern, whereby alkanes
are regioselectively hydroxylated even in the presence of a double bond. Reaction barriers of propene
epoxidation and hydroxylation are almost identical to ones observed for a cytochrome P450 catalyst and
significantly higher than those obtained for a horseradish peroxidase catalyst. It is shown that the regioselectivity
difference is entropy and thermally driven and that the electron-transfer processes that occur during the reaction
mechanism follow cytochrome P450-type patterns in the hydroxylation reaction
Preferential hydroxylation over epoxidation catalysis by a horseradish peroxidase mutant: A cytochrome P450 mimic
No full textDensity functional theory calculations are presented on the catalytic properties of a horseradish peroxidase mutant whereby the axial nitrogen atom is replaced by phosphorus. This mutant has never been studied experimentally and only one theoretical report on this system is known (de Visser, S. P. J. Phys. Chem. B 2006, 110, 20759-20761). Thus, a one-atom substitution in horseradish peroxidase changes the properties of the catalytic center of the enzyme to more cytochrome P450-type qualities. In particular, the phosphorussubstituted horseradish peroxidase mutant reacts with substrates via a unique reactivity pattern, whereby alkanes are regioselectively hydroxylated even in the presence of a double bond. Reaction barriers of propene epoxidation and hydroxylation are almost identical to ones observed for a cytochrome P450 catalyst and significantly higher than those obtained for a horseradish peroxidase catalyst. It is shown that the regioselectivity difference is entropy and thermally driven and that the electron-transfer processes that occur during the reaction mechanism follow cytochrome P450-type patterns in the hydroxylation reaction. © 2007 American Chemical Society
A comprehensive test set of epoxidation rate constants for iron(IV)-oxo porphyrin cation radical complexes
Get PDFCytochrome P450 enzymes are heme based monoxygenases that catalyse a range of oxygen atom transfer reactions with various substrates, including aliphatic and aromatic hydroxylation as well as epoxidation reactions. The active species is short-lived and difficult to trap and characterize experimentally, moreover, it reacts in a regioselective manner with substrates leading to aliphatic hydroxylation and epoxidation products,
but the origin of this regioselectivity is poorly understood. We have synthesized a model complex and studied it with low-pressure Fourier transform-ion cyclotron resonance (FT-ICR) mass spectrometry (MS). A novel approach was devised using the reaction of [FeIII(TPFPP)]+ (TPFPP 1⁄4 meso-tetrakis(pentafluorophenyl) porphinato dianion) with iodosylbenzene as a terminal oxidant which leads to the production of ions
corresponding to [FeIV(O)(TPFPP+c)]+. This species was isolated in the gas-phase and studied in its reactivity with a variety of olefins. Product patterns and rate constants under Ideal Gas conditions were determined by FT-ICR MS. All substrates react with [FeIV(O)(TPFPP+c)]+ by a more or less efficient oxygen atom transfer process. In addition, substrates with low ionization energies react by a charge-transfer channel, which
enabled us to determine the electron affinity of [FeIV(O)(TPFPP+c)]+ for the first time. Interestingly, no hydrogen atom abstraction pathways are observed for the reaction of [FeIV(O)(TPFPP+c)]+ with prototypical olefins such as propene, cyclohexene and cyclohexadiene and also no kinetic isotope effect in the reaction rate is found, which suggests that the competition between epoxidation and hydroxylation – in the gas-phase
– is in favour of substrate epoxidation. This notion further implies that P450 enzymes will need to adapt their substrate binding pocket, in order to enable favourable aliphatic hydroxylation over double bond epoxidation pathways. The MS studies yield a large test-set of experimental reaction rates of iron(IV)–oxo porphyrin cation radical complexes, so far unprecedented in the gas-phase, providing a benchmark for calibration studies using
computational techniques. Preliminary computational results presented here confirm the observed trends excellently and rationalize the reactivities within the framework of thermochemical considerations and valence bond schemes
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