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Haoming Zhang - One of the best experts on this subject based on the ideXlab platform.
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cytochrome b5 increases the rate of Product Formation by cytochrome p450 2b4 and competes with cytochrome p450 reductase for a binding site on cytochrome p450 2b4
Journal of Biological Chemistry, 2007Co-Authors: Haoming ZhangAbstract:Abstract The kinetics of Product Formation by cytochrome P450 2B4 were compared in the presence of cytochrome b5 (cyt b5) and NADPH-cyt P450 reductase (CPR) under conditions in which cytochrome P450 (cyt P450) underwent a single catalytic cycle with two substrates, benzphetamine and cyclohexane. At a cyt P450:cyt b5 molar ratio of 1:1 under single turnover conditions, cyt P450 2B4 catalyzes the oxidation of the substrates, benzphetamine and cyclohexane, with rate constants of 18 ± 2 and 29 ± 4.5 s–1, respectively. Approximately 500 pmol of norbenzphetamine and 58 pmol of cyclohexanol were formed per nmol of cyt P450. In marked contrast, at a cyt P450:CPR molar ratio of 1:1, cyt P450 2B4 catalyzes the oxidation of benzphetamine ≅100-fold (k = 0.15 ± 0.05 s–1) and cyclohexane ≅10-fold (k = 2.5 ± 0.35 s–1) more slowly. Four hundred picomoles of norbenzphetamine and 21 pmol of cyclohexanol were formed per nmol of cyt P450. In the presence of equimolar concentrations of cyt P450, cyt b5, and CPR, Product Formation is biphasic and occurs with fast and slow rate constants characteristic of catalysis by cyt b5 and CPR. Increasing the concentration of cyt b5 enhanced the amount of Product formed by cyt b5 while decreasing the amount of Product generated by CPR. Under steady-state conditions at all cyt b5:cyt P450 molar ratios examined, cyt b5 inhibits the rate of NADPH consumption. Nevertheless, at low cyt b5:cyt P450 molar ratios ≤1:1, the rate of metabolism of cyclohexane and benzphetamine is enhanced, whereas at higher cyt b5:cyt P450 molar ratios, cyt b5 progressively inhibits both NADPH consumption and the rate of metabolism. It is proposed that the ability of cyt b5 to enhance substrate metabolism by cyt P450 is related to its ability to increase the rate of catalysis and that the inhibitory properties of cyt b5 are because of its ability to occupy the reductase-binding site on cyt P450 2B4, thereby preventing reduction of ferric cyt P450 and initiation of the catalytic cycle. It is proposed that cyt b5 and CPR compete for a binding site on cyt P450 2B4.
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cytochrome b5 increases the rate of Product Formation by cytochrome p450 2b4 and competes with cytochrome p450 reductase for a binding site on cytochrome p450 2b4
Journal of Biological Chemistry, 2007Co-Authors: Haoming Zhang, Lucy WaskellAbstract:The kinetics of Product Formation by cytochrome P450 2B4 were compared in the presence of cytochrome b(5) (cyt b(5)) and NADPH-cyt P450 reductase (CPR) under conditions in which cytochrome P450 (cyt P450) underwent a single catalytic cycle with two substrates, benzphetamine and cyclohexane. At a cyt P450:cyt b(5) molar ratio of 1:1 under single turnover conditions, cyt P450 2B4 catalyzes the oxidation of the substrates, benzphetamine and cyclohexane, with rate constants of 18 +/- 2 and 29 +/- 4.5 s(-1), respectively. Approximately 500 pmol of norbenzphetamine and 58 pmol of cyclohexanol were formed per nmol of cyt P450. In marked contrast, at a cyt P450:CPR molar ratio of 1:1, cyt P450 2B4 catalyzes the oxidation of benzphetamine congruent with100-fold (k = 0.15 +/- 0.05 s(-1)) and cyclohexane congruent with10-fold (k = 2.5 +/- 0.35 s(-1)) more slowly. Four hundred picomoles of norbenzphetamine and 21 pmol of cyclohexanol were formed per nmol of cyt P450. In the presence of equimolar concentrations of cyt P450, cyt b(5), and CPR, Product Formation is biphasic and occurs with fast and slow rate constants characteristic of catalysis by cyt b(5) and CPR. Increasing the concentration of cyt b(5) enhanced the amount of Product formed by cyt b(5) while decreasing the amount of Product generated by CPR. Under steady-state conditions at all cyt b(5):cyt P450 molar ratios examined, cyt b(5) inhibits the rate of NADPH consumption. Nevertheless, at low cyt b(5):cyt P450 molar ratios
Lucy Waskell - One of the best experts on this subject based on the ideXlab platform.
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cytochrome b5 increases the rate of Product Formation by cytochrome p450 2b4 and competes with cytochrome p450 reductase for a binding site on cytochrome p450 2b4
Journal of Biological Chemistry, 2007Co-Authors: Haoming Zhang, Lucy WaskellAbstract:The kinetics of Product Formation by cytochrome P450 2B4 were compared in the presence of cytochrome b(5) (cyt b(5)) and NADPH-cyt P450 reductase (CPR) under conditions in which cytochrome P450 (cyt P450) underwent a single catalytic cycle with two substrates, benzphetamine and cyclohexane. At a cyt P450:cyt b(5) molar ratio of 1:1 under single turnover conditions, cyt P450 2B4 catalyzes the oxidation of the substrates, benzphetamine and cyclohexane, with rate constants of 18 +/- 2 and 29 +/- 4.5 s(-1), respectively. Approximately 500 pmol of norbenzphetamine and 58 pmol of cyclohexanol were formed per nmol of cyt P450. In marked contrast, at a cyt P450:CPR molar ratio of 1:1, cyt P450 2B4 catalyzes the oxidation of benzphetamine congruent with100-fold (k = 0.15 +/- 0.05 s(-1)) and cyclohexane congruent with10-fold (k = 2.5 +/- 0.35 s(-1)) more slowly. Four hundred picomoles of norbenzphetamine and 21 pmol of cyclohexanol were formed per nmol of cyt P450. In the presence of equimolar concentrations of cyt P450, cyt b(5), and CPR, Product Formation is biphasic and occurs with fast and slow rate constants characteristic of catalysis by cyt b(5) and CPR. Increasing the concentration of cyt b(5) enhanced the amount of Product formed by cyt b(5) while decreasing the amount of Product generated by CPR. Under steady-state conditions at all cyt b(5):cyt P450 molar ratios examined, cyt b(5) inhibits the rate of NADPH consumption. Nevertheless, at low cyt b(5):cyt P450 molar ratios
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the stoichiometry of the cytochrome p 450 catalyzed metabolism of methoxyflurane and benzphetamine in the presence and absence of cytochrome b5
Journal of Biological Chemistry, 1995Co-Authors: Larry D Gruenke, Krystyna Konopka, Marie Cadieu, Lucy WaskellAbstract:The complete stoichiometry of the metabolism of the cytochrome b5 (cyt b5)-requiring substrate, methoxyflurane, by purified cytochrome P-450 2B4 was compared to that of another substrate, benzphetamine, which does not require cyt b5 for its metabolism. Cyt b5 invariably improved the efficiency of Product Formation. That is, in the presence of cyt b5 a greater percentage of the reducing equivalents from NADPH were utilized to generate substrate metabolites, primarily at the expense of the side Product, superoxide. With methoxyflurane, cyt b5 addition always resulted in an increased rate of Product Formation, while with benzphetamine the rate of Product Formation remained unchanged, increased or decreased. The apparently contradictory observations of increased reaction efficiency but decrease in total Product Formation for benzphetamine can be explained by a second effect of cyt b5. Under some experimental conditions cyt b5 inhibits total NADPH consumption. Whether stimulation, inhibition, or no change in Product Formation is observed in the presence of cyt b5 depends on the net effect of the stimulatory and inhibitory effects of cyt b5. When total NADPH consumption is inhibited by cyt b5, the rapidly metabolized, highly coupled (approximately equal to 50%) substrate, benzphetamine, undergoes a net decrease in metabolism not counterbalanced by the increase in the efficiency (2-20%) of the reaction. In contrast, in the presence of the slowly metabolized, poorly coupled (approximately equal to 0.5-3%) substrate, methoxyflurane, inhibition of total NADPH consumption by cyt b5 was never sufficient to overcome the stimulation of Product Formation due to an increase in efficiency of the reaction.
David L Osborn - One of the best experts on this subject based on the ideXlab platform.
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time resolved measurements of Product Formation in the low temperature 550 675 k oxidation of neopentane a probe to investigate chain branching mechanism
Physical Chemistry Chemical Physics, 2017Co-Authors: Arkke J Eskola, John D Savee, David L Osborn, Ivan O Antonov, Leonid Sheps, Craig A TaatjesAbstract:Product Formation, in particular ketohydroperoxide Formation and decomposition, were investigated in time-resolved, Cl-atom initiated neopentane oxidation experiments in the temperature range 550–675 K using a photoionization time-of-flight mass spectrometer. Ionization light was provided either by Advanced Light Source tunable synchrotron radiation or ∼10.2 eV fixed energy radiation from a H2-discharge lamp. Experiments were performed both at 1–2 atm pressure using a high-pressure reactor and also at ∼9 Torr pressure employing a low-pressure reactor for comparison. Because of the highly symmetric structure of neopentane, ketohydroperoxide signal can be attributed to a 3-hydroperoxy-2,2-dimethylpropanal isomer, i.e. from a γ-ketohydroperoxide (γ-KHP). The photoionization spectra of the γ-KHP measured at low- and high pressures and varying oxygen concentrations agree well with each other, further supporting they originate from the single isomer. Measurements performed in this work also suggest that the “Korcek” mechanism may play an important role in the decomposition of 3-hydroperoxy-2,2-dimethylpropanal, especially at lower temperatures. However, at higher temperatures where γ-KHP decomposition to hydroxyl radical and oxy-radical dominates, oxidation of the oxy-radical yields a new important channel leading to acetone, carbon monoxide, and OH radical. Starting from the initial neopentyl + O2 reaction, this channel releases altogether three OH radicals. A strongly temperature-dependent reaction Product is observed at m/z = 100, likely attributable to 2,2-dimethylpropanedial.
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the c 3p nh3 reaction in interstellar chemistry i investigation of the Product Formation channels
arXiv: Astrophysics of Galaxies, 2016Co-Authors: Jeremy Bourgalais, David L Osborn, Michael Capron, Ranjith Kumar Abhinavam Kailasanathan, Kevin M Hickson, Jeanchristophe Loison, Valentine Wakelam, Fabien GoulayAbstract:The Product Formation channels of ground state carbon atoms, C(3P), reacting with ammonia, NH3, have been investigated using two complementary experiments and electronic structure calculations. Reaction Products are detected in a gas flow tube experiment (330 K, 4 Torr) using tunable VUV photoionization coupled with time of flight mass spectrometry. Temporal profiles of the species formed and photoionization spectra are used to identify primary Products of the C + NH3 reaction. In addition, H-atom Formation is monitored by VUV laser induced fluorescence from room temperature to 50 K in a supersonic gas flow generated by the Laval nozzle technique. Electronic structure calculations are performed to derive intermediates, transition states and complexes formed along the reaction coordinate. The combination of photoionization and laser induced fluorescence experiments supported by theoretical calculations indicate that in the temperature and pressure range investigated, the H + H2CN Production channel represents 100% of the Product yield for this reaction. Kinetics measurements of the title reaction down to 50 K and the effect of the new rate constants on interstellar nitrogen hydride abundances using a model of dense interstellar clouds are reported in paper II.
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the c 3p nh3 reaction in interstellar chemistry i investigation of the Product Formation channels
The Astrophysical Journal, 2015Co-Authors: Jeremy Bourgalais, David L Osborn, Michael Capron, Ranjith Kumar Abhinavam Kailasanathan, Kevin M Hickson, Jeanchristophe Loison, Valentine Wakelam, Fabien GoulayAbstract:The Product Formation channels of ground state carbon atoms, C(3P), reacting with ammonia, NH3, have been investigated using two complementary experiments and electronic structure calculations. Reaction Products are detected in a gas flow tube experiment (330 K, 4 Torr) using tunable vacuum-ultraviolet (VUV) photoionization coupled with time of flight mass spectrometry. Temporal profiles of the species formed and photoionization spectra are used to identify primary Products of the C + NH3 reaction. In addition, H-atom Formation is monitored by VUV laser induced fluorescence (LIF) from room temperature to 50 K in a supersonic gas flow generated by the Laval nozzle technique. Electronic structure calculations are performed to derive intermediates, transition states, and complexes formed along the reaction coordinate. The combination of photoionization and LIF experiments supported by theoretical calculations indicate that in the temperature and pressure range investigated, the H + H2CN Production channel represents 100% of the Product yield for this reaction. As a result, kinetics measurements of the title reaction down to 50 K and the effect of the new rate constants on interstellar nitrogen hydride abundances using a model of dense interstellar clouds are reported in Paper II.
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synchrotron photoionization mass spectrometry measurements of Product Formation in low temperature n butane oxidation toward a fundamental understanding of autoignition chemistry and n c4h9 o2 s c4h9 o2 reactions
Journal of Physical Chemistry A, 2013Co-Authors: Arkke J Eskola, Oliver Welz, John D Savee, David L Osborn, Craig A TaatjesAbstract:Product Formation in the laser-initiated low-temperature (575–700 K) oxidation of n-butane was investigated by using tunable synchrotron photoionization time-of-flight mass spectrometry at low pressure (∼4 Torr). Oxidation was triggered either by 351 nm photolysis of Cl2 and subsequent fast Cl + n-butane reaction or by 248 nm photolysis of 1-iodobutane or 2-iodobutane. Iodobutane photolysis allowed isomer-specific preparation of either n-C4H9 or s-C4H9 radicals. Experiments probed the time-resolved Formation of Products and identified isomeric species by their photoionization spectra. For stable primary Products of butyl + O2 reactions (e.g., butene or oxygen heterocycles) bimodal time behavior is observed; the initial prompt Formation, primarily due to chemical activation, is followed by a slower component arising from the dissociation of thermalized butylperoxy or hydroperoxybutyl radicals. In addition, time-resolved Formation of C4-ketohydroperoxides (C4H8O3, m/z = 104) was observed in the n-C4H9 + O2 ...
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synchrotron photoionization measurements of fundamental autoignition reactions Product Formation in low temperature isobutane oxidation
Proposed for publication in Proceedings of the Combustion Institute., 2013Co-Authors: Arkke J Eskola, Oliver Welz, John D Savee, David L Osborn, Craig A TaatjesAbstract:Abstract Product Formation in laser-photolytic Cl-initiated low-temperature (550–700 K) oxidation of isobutane in a slow-flow reactor was investigated by tunable synchrotron photoionization mass spectrometry. These experiments probed the time-resolved Formation of Products following photolytic initiation of the oxidation, and identify isomeric species by their photoionization spectra. The relative yields of oxygenated Product isomers (2,2-dimethyloxirane, methylpropanal, and 3-methyloxetane) are in reasonable concord with measurements from Walker and co-workers (J. Chem. Soc. Faraday Trans. 74 (1) (1978) 2229–2251) at higher temperature. Oxidation of isotopically labeled isobutane, (CH 3 ) 3 CD, suggests that methylpropanal Formation can proceed from both (CH 3 ) 2 CCH 2 OOH and CH 3 CH(CH 2 )CH 2 OOH isomers. Bimodal time behavior is observed for Product Formation; the initial prompt Formation reflects “formally direct” channels, principally chemical activation, and the longer-timescale “delayed” component arises from dissociation of thermalized ROO and QOOH radicals. The proportion of prompt to delayed signal is smaller for the oxygenated Products than for the isobutene Product. This channel-specific behavior can be qualitatively understood by considering the different energetic distributions of ROO and QOOH in formally direct vs. thermal channels and the fact that the transition states involved in the Formation of oxygenated Products are “tighter” than that for isobutene Formation.
Arkke J Eskola - One of the best experts on this subject based on the ideXlab platform.
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time resolved measurements of Product Formation in the low temperature 550 675 k oxidation of neopentane a probe to investigate chain branching mechanism
Physical Chemistry Chemical Physics, 2017Co-Authors: Arkke J Eskola, John D Savee, David L Osborn, Ivan O Antonov, Leonid Sheps, Craig A TaatjesAbstract:Product Formation, in particular ketohydroperoxide Formation and decomposition, were investigated in time-resolved, Cl-atom initiated neopentane oxidation experiments in the temperature range 550–675 K using a photoionization time-of-flight mass spectrometer. Ionization light was provided either by Advanced Light Source tunable synchrotron radiation or ∼10.2 eV fixed energy radiation from a H2-discharge lamp. Experiments were performed both at 1–2 atm pressure using a high-pressure reactor and also at ∼9 Torr pressure employing a low-pressure reactor for comparison. Because of the highly symmetric structure of neopentane, ketohydroperoxide signal can be attributed to a 3-hydroperoxy-2,2-dimethylpropanal isomer, i.e. from a γ-ketohydroperoxide (γ-KHP). The photoionization spectra of the γ-KHP measured at low- and high pressures and varying oxygen concentrations agree well with each other, further supporting they originate from the single isomer. Measurements performed in this work also suggest that the “Korcek” mechanism may play an important role in the decomposition of 3-hydroperoxy-2,2-dimethylpropanal, especially at lower temperatures. However, at higher temperatures where γ-KHP decomposition to hydroxyl radical and oxy-radical dominates, oxidation of the oxy-radical yields a new important channel leading to acetone, carbon monoxide, and OH radical. Starting from the initial neopentyl + O2 reaction, this channel releases altogether three OH radicals. A strongly temperature-dependent reaction Product is observed at m/z = 100, likely attributable to 2,2-dimethylpropanedial.
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synchrotron photoionization mass spectrometry measurements of Product Formation in low temperature n butane oxidation toward a fundamental understanding of autoignition chemistry and n c4h9 o2 s c4h9 o2 reactions
Journal of Physical Chemistry A, 2013Co-Authors: Arkke J Eskola, Oliver Welz, John D Savee, David L Osborn, Craig A TaatjesAbstract:Product Formation in the laser-initiated low-temperature (575–700 K) oxidation of n-butane was investigated by using tunable synchrotron photoionization time-of-flight mass spectrometry at low pressure (∼4 Torr). Oxidation was triggered either by 351 nm photolysis of Cl2 and subsequent fast Cl + n-butane reaction or by 248 nm photolysis of 1-iodobutane or 2-iodobutane. Iodobutane photolysis allowed isomer-specific preparation of either n-C4H9 or s-C4H9 radicals. Experiments probed the time-resolved Formation of Products and identified isomeric species by their photoionization spectra. For stable primary Products of butyl + O2 reactions (e.g., butene or oxygen heterocycles) bimodal time behavior is observed; the initial prompt Formation, primarily due to chemical activation, is followed by a slower component arising from the dissociation of thermalized butylperoxy or hydroperoxybutyl radicals. In addition, time-resolved Formation of C4-ketohydroperoxides (C4H8O3, m/z = 104) was observed in the n-C4H9 + O2 ...
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synchrotron photoionization measurements of fundamental autoignition reactions Product Formation in low temperature isobutane oxidation
Proposed for publication in Proceedings of the Combustion Institute., 2013Co-Authors: Arkke J Eskola, Oliver Welz, John D Savee, David L Osborn, Craig A TaatjesAbstract:Abstract Product Formation in laser-photolytic Cl-initiated low-temperature (550–700 K) oxidation of isobutane in a slow-flow reactor was investigated by tunable synchrotron photoionization mass spectrometry. These experiments probed the time-resolved Formation of Products following photolytic initiation of the oxidation, and identify isomeric species by their photoionization spectra. The relative yields of oxygenated Product isomers (2,2-dimethyloxirane, methylpropanal, and 3-methyloxetane) are in reasonable concord with measurements from Walker and co-workers (J. Chem. Soc. Faraday Trans. 74 (1) (1978) 2229–2251) at higher temperature. Oxidation of isotopically labeled isobutane, (CH 3 ) 3 CD, suggests that methylpropanal Formation can proceed from both (CH 3 ) 2 CCH 2 OOH and CH 3 CH(CH 2 )CH 2 OOH isomers. Bimodal time behavior is observed for Product Formation; the initial prompt Formation reflects “formally direct” channels, principally chemical activation, and the longer-timescale “delayed” component arises from dissociation of thermalized ROO and QOOH radicals. The proportion of prompt to delayed signal is smaller for the oxygenated Products than for the isobutene Product. This channel-specific behavior can be qualitatively understood by considering the different energetic distributions of ROO and QOOH in formally direct vs. thermal channels and the fact that the transition states involved in the Formation of oxygenated Products are “tighter” than that for isobutene Formation.
Craig A Taatjes - One of the best experts on this subject based on the ideXlab platform.
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time resolved measurements of Product Formation in the low temperature 550 675 k oxidation of neopentane a probe to investigate chain branching mechanism
Physical Chemistry Chemical Physics, 2017Co-Authors: Arkke J Eskola, John D Savee, David L Osborn, Ivan O Antonov, Leonid Sheps, Craig A TaatjesAbstract:Product Formation, in particular ketohydroperoxide Formation and decomposition, were investigated in time-resolved, Cl-atom initiated neopentane oxidation experiments in the temperature range 550–675 K using a photoionization time-of-flight mass spectrometer. Ionization light was provided either by Advanced Light Source tunable synchrotron radiation or ∼10.2 eV fixed energy radiation from a H2-discharge lamp. Experiments were performed both at 1–2 atm pressure using a high-pressure reactor and also at ∼9 Torr pressure employing a low-pressure reactor for comparison. Because of the highly symmetric structure of neopentane, ketohydroperoxide signal can be attributed to a 3-hydroperoxy-2,2-dimethylpropanal isomer, i.e. from a γ-ketohydroperoxide (γ-KHP). The photoionization spectra of the γ-KHP measured at low- and high pressures and varying oxygen concentrations agree well with each other, further supporting they originate from the single isomer. Measurements performed in this work also suggest that the “Korcek” mechanism may play an important role in the decomposition of 3-hydroperoxy-2,2-dimethylpropanal, especially at lower temperatures. However, at higher temperatures where γ-KHP decomposition to hydroxyl radical and oxy-radical dominates, oxidation of the oxy-radical yields a new important channel leading to acetone, carbon monoxide, and OH radical. Starting from the initial neopentyl + O2 reaction, this channel releases altogether three OH radicals. A strongly temperature-dependent reaction Product is observed at m/z = 100, likely attributable to 2,2-dimethylpropanedial.
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synchrotron photoionization mass spectrometry measurements of Product Formation in low temperature n butane oxidation toward a fundamental understanding of autoignition chemistry and n c4h9 o2 s c4h9 o2 reactions
Journal of Physical Chemistry A, 2013Co-Authors: Arkke J Eskola, Oliver Welz, John D Savee, David L Osborn, Craig A TaatjesAbstract:Product Formation in the laser-initiated low-temperature (575–700 K) oxidation of n-butane was investigated by using tunable synchrotron photoionization time-of-flight mass spectrometry at low pressure (∼4 Torr). Oxidation was triggered either by 351 nm photolysis of Cl2 and subsequent fast Cl + n-butane reaction or by 248 nm photolysis of 1-iodobutane or 2-iodobutane. Iodobutane photolysis allowed isomer-specific preparation of either n-C4H9 or s-C4H9 radicals. Experiments probed the time-resolved Formation of Products and identified isomeric species by their photoionization spectra. For stable primary Products of butyl + O2 reactions (e.g., butene or oxygen heterocycles) bimodal time behavior is observed; the initial prompt Formation, primarily due to chemical activation, is followed by a slower component arising from the dissociation of thermalized butylperoxy or hydroperoxybutyl radicals. In addition, time-resolved Formation of C4-ketohydroperoxides (C4H8O3, m/z = 104) was observed in the n-C4H9 + O2 ...
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synchrotron photoionization measurements of fundamental autoignition reactions Product Formation in low temperature isobutane oxidation
Proposed for publication in Proceedings of the Combustion Institute., 2013Co-Authors: Arkke J Eskola, Oliver Welz, John D Savee, David L Osborn, Craig A TaatjesAbstract:Abstract Product Formation in laser-photolytic Cl-initiated low-temperature (550–700 K) oxidation of isobutane in a slow-flow reactor was investigated by tunable synchrotron photoionization mass spectrometry. These experiments probed the time-resolved Formation of Products following photolytic initiation of the oxidation, and identify isomeric species by their photoionization spectra. The relative yields of oxygenated Product isomers (2,2-dimethyloxirane, methylpropanal, and 3-methyloxetane) are in reasonable concord with measurements from Walker and co-workers (J. Chem. Soc. Faraday Trans. 74 (1) (1978) 2229–2251) at higher temperature. Oxidation of isotopically labeled isobutane, (CH 3 ) 3 CD, suggests that methylpropanal Formation can proceed from both (CH 3 ) 2 CCH 2 OOH and CH 3 CH(CH 2 )CH 2 OOH isomers. Bimodal time behavior is observed for Product Formation; the initial prompt Formation reflects “formally direct” channels, principally chemical activation, and the longer-timescale “delayed” component arises from dissociation of thermalized ROO and QOOH radicals. The proportion of prompt to delayed signal is smaller for the oxygenated Products than for the isobutene Product. This channel-specific behavior can be qualitatively understood by considering the different energetic distributions of ROO and QOOH in formally direct vs. thermal channels and the fact that the transition states involved in the Formation of oxygenated Products are “tighter” than that for isobutene Formation.
