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Elimination Kinetics (elimination + kinetics)

Distribution by Scientific Domains

Chemistry	46%
Life Sciences	40%

Selected Abstracts

Michaelis-Menten Elimination Kinetics of Acetaldehyde During Ethanol Oxidation

ALCOHOLISM, Issue 2002
Tatsuya Fujimiya
Background Acetaldehyde (AcH) is a toxic metabolite of ethanol (EtOH). The pharmacokinetics of blood AcH during EtOH oxidation was studied with or without the administration of aldehyde dehydrogenase 2 inhibitor (cyanamide) in rabbits. Methods An bolus of EtOH saline solution (0.25, 0.5, 1.0, 1.5, and 2.0 g/kg) was injected intravenously. Cyanamide was administered intraperitoneally (25 mg/kg body weight) to the cyanamide-treated group. Blood EtOH and AcH concentrations were measured by using head-space gas chromatography. Results In the control group, the first peak of the blood AcH appeared immediately and the second elevation appeared 1 to 4 hr after administration at a high EtOH dose. The blood AcH levels other than the second elevation part were significantly correlated to the blood EtOH levels. In the cyanamide-treated group, a peak and a plateau formed at the time corresponding to the second peak in the control group. The peak and plateau concentration of AcH increased markedly. We attempted simultaneous curve fitting, using the five blood EtOH and AcH concentration-time curves, to determine the pharmacokinetic model. Consequently, the AcH elimination was best described by a Michaelis-Menten kinetic model in both groups. Conclusions The blood AcH profile was suggested to consist of the first and second components that are related to the blood EtOH concentration itself and the metabolic formation of AcH, respectively. With higher EtOH doses or aldehyde dehydrogenase 2 inhibition, the second component becomes prominent as a result of the capacity-limited property of the metabolism of AcH, which is described by Michaelis-Menten elimination kinetics. [source]

Effect of Amino Acids on Acrylamide Formation and Elimination Kinetics

BIOTECHNOLOGY PROGRESS, Issue 5 2005
Wendie L. Claeys
The effect of amino acids other than asparagine on acrylamide (AA) formation/elimination kinetics was studied in an asparagine-glucose model system (0.01 M, pH 6) heated at temperatures between 140 and 200 °C. Addition of cysteine or lysine to the model significantly lowered the AA yield, whereas addition of glutamine had a strong promoting effect and of alanine a rather neutral effect on the AA formation. This was also reflected by AA formation/elimination kinetics, which for all model systems studied could be modeled by two consecutive first-order reactions. The ratio of the elimination to the formation rate constant increased from the systems to which glutamine or alanine was added, over the control model system, to the model systems that contained lysine or cysteine. [source]

Relation between metal concentration in water and metal content of marine mussels (Mytilus galloprovincialis): Impact of physiology,

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 7 2008
Stellio Casas
Abstract The present study constitutes an in situ investigation of metal kinetics within soft tissue of mussels (Mytilus gallo-provincialis), which solves the problem of the decoupling of the effect of animal physiology and metal bioavailability in water. Field experiments were conducted to measure uptake and elimination kinetics for four metals (Hg, Pb, Cd, and Cu) in three Mediterranean sites with different contamination and nutritive levels. At each site, metal concentrations were monitored in soft tissues of mussels and in the surrounding waters. The experimental conditions were completely characterized: Lazaret Bay (located between Nice and Marseille, France) is a hot spot for Hg (6.3 ng/L) and Pb (163 ng/L) concentrations and is an oligotrophic, stable site; Bages Lagoon (located to the west of Montpellier, France) is particularly contaminated by Cd (1.5 ng/L) and Cu (1.5,g/L) and is a mesotrophic site where variability of trophic and physicochemical parameters is significant; and Port-Cros Island (located in the Hyeres National Park, France) is considered to be a reference site. Those kinetics permit us to decouple physiological, chemical, and environmental interactions. After normalizing mussel metal content for similar physiological conditions, application of the local weighted regression (LOWESS) statistical treatment shows a parallelism between the time trends of metal concentrations in the bivalve and metal concentrations in water. The results enabled us to obtain in situ kinetic parameters and realistic bioaccumulation factors. Their logarithmic values were 4.6 for Hg, 4.3 for Pb, 4.9 for Cd, and 3.9 for Cu. The importance of physiological processes such as spawning is discussed as a factor influencing the bioaccumulation factor. This information may be useful in refining monitoring tools for risk assessment and, more generally, in environmental management strategies. [source]

Determination of polychlorinated biphenyl and polycyclic aromatic hydrocarbon elimination rates in adult green and leopard frogs

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2006
Jocelyn L. Leney
Abstract The purpose of the present study was to quantify elimination kinetics of polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) in adult green frogs (Rana clamitans) and leopard frogs (Rana pipiens). Three experiments were conducted: PCB elimination rate constants were determined for both frog species, and PAH elimination rate constants were determined for leopard frogs only. In green frogs, significant PCB elimination rate constants ranged from 0.013 to 0.04 d,1 (time for frogs to achieve 90% steady state with water [t90] = 57.8-178.2 d). In leopard frogs, significant PCB elimination rate constants ranged from 0.004 to 0.047 d,1 (t90 = 48.8-657.9 d). Polycyclic aromatic hydrocarbon elimination in leopard frogs was faster than PCB elimination in either frog species: Significant PAH rate constants ranged from 0.069 to 0.188 d,1 (t90 = 12.2-33.5 d). In both species, and for both PCBs and PAHs, a significant inverse relationship was found between the chemical elimination rate constant and Kow. These results show that adult anurans have relatively low elimination rates of PCBs but exhibit a small capacity for metabolic biotransformation of PAHs that is comparable to that of invertebrates but lower than that of fish. These findings suggest that adult amphibians have the potential to be used as biomonitors for persistent organic chemicals. [source]

Homogeneous, unimolecular gas-phase elimination kinetics of ethyl esters of glyoxylic, 2-oxo-propanoic, and 3-methyl-2-oxo-butanoic acids

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 5 2007
Andreina Reyes
The rates of elimination of several ethyl esters of 2-oxo-carboxylic acid were determined in a seasoned static reaction vessel over the temperature range 350,430°C and pressure range 33,240 Torr. The reactions, in the presence of a free-radical inhibitor, are homogeneous, unimolecular, and follow a first-order rate law. The overall and partial rate coefficients are expressed by the Arrhenius equation. Ethyl glyoxalate Ethyl 2-oxo-propionate Ethyl 3-methyl-2-oxo-butyrate The mechanisms of these elimination reactions are described in terms of concerted cyclic transition state structures. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 268,275, 2007 [source]

Ab initio and DFT calculations of benzaldoxime elimination kinetics in the gas phase

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 10 2008
Jose R. Mora
Abstract The mechanism for the gas-phase molecular elimination kinetics of benzaldoxime was examined at MP2/6-31G, MP2/6-31G(d,p), B3LYP/6-31G, B3LYP/6-31G(d,p), MPW1PW91/6-31G, and MPW1PW91/6-31G(d,p) levels of theory. The products of elimination of this oxime are benzonitrile and water. Calculated thermodynamic and kinetic parameters estimated from B3LYP/6-31G was found to be in better agreement with the experimental values. Transition state structure is best described as a four-membered cyclic structure with good approximation to planarity. NBO charges analysis revealed a little greater polarization of the benzylic C,H,+ rather than N,OH,,. Bond indexes and synchronicity parameters are in agreement with a concerted semi-polar type of mechanism with benzylic CH bond breaking as determining step of the reaction. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source]

The mechanisms of the homogeneous, unimolecular, elimination kinetics of several , -substituted diethyl acetals in the gas-phase

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 9 2010
José R. Mora
Abstract The rates of gas-phase elimination of several , -substituted diethyl acetals have been determined in a static system and seasoned with allyl bromide. The reactions, inhibited with toluene, are homogeneous, unimolecular, and follow first-order law kinetics. These elimination processes involve two parallel reactions. The first parallel reaction yields ethanol and the corresponding ethyl vinyl ether. The latter product is an unstable intermediate and further decomposes to ethylene and the corresponding substituted aldehyde. The second parallel reaction gives ethane and the corresponding ethyl ester. The kinetics has been measured over the temperature range of 370,441,°C and pressure range of 23,160,torr. The rate coefficients are given by the following Arrhenius equations: The differences in the rates of ethanol formation may be attributed to electronic transmission of the , -substituent. The comparative kinetic and thermodynamic parameters of the parallel reactions suggest two different concerted polar four-membered cyclic transition state types of mechanisms. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Joint theoretical and experimental study of the gas-phase elimination kinetics of tert -butyl ester of carbamic, N, N -dimethylcarbamic, N -hydroxycarbamic acids and 1-(tert -butoxycarbonyl)-imidazole

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 12 2007
Jose R Mora
Abstract The gas-phase elimination kinetics of the title compounds were carried out in a static reaction system and seasoned with allyl bromide. The working temperature and pressure ranges were 200,280,°C and 22,201.5,Torr, respectively. The reactions are homogeneous, unimolecular, and follow a first-order rate law. These substrates produce isobutene and corresponding carbamic acid in the rate-determining step. The unstable carbamic acid intermediate rapidly decarboxylates through a four-membered cyclic transition state (TS) to give the corresponding organic nitrogen compound. The temperature dependence of the rate coefficients is expressed by the following Arrhenius equations: for tert -butyl carbamate logk1 (s,1),=,(13.02,±,0.46),,,(161.6,±,4.7) kJ/mol(2.303,RT),1, for tert -butyl N -hydroxycarbamate logk1 (s,1),=,(12.52,±,0.11),,,(147.8,±,1.1) kJ/mol(2.303,RT),1, and for 1-(tert -butoxycarbonyl)-imidazole logk1 (s,1),= (11.63,±,0.21),(134.9,±,2.0) kJ/mol(2.303,RT),1. Theoretical studies of these elimination were performed at Møller,Plesset MP2/6-31G and DFT B3LYP/6-31G(d), B3LYP/6-31G(d,p) levels of theory. The calculated bond orders, NBO charges, and synchronicity (Sy) indicate that these reactions are concerted, slightly asynchronous, and proceed through a six-membered cyclic TS type. Results for estimated kinetic and thermodynamic parameters are discussed in terms of the proposed reaction mechanism and TS structure. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Experimental and theoretical studies of the elimination kinetics of 3-hydroxy-3-methyl-2-butanone in the gas phase

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 7 2005
Mariana Graterol
Abstract The kinetics of the gas-phase elimination of 3-hydroxy-3-methyl-2-butanone was investigated in a static system, seasoned with allyl bromide, and in the presence of the free chain radical inhibitor toluene. The working temperature and pressure range were 439.6,489.3°C and 81,201.5,Torr (1,Torr,=,133.3,Pa), respectively. The reaction was found to be homogeneous, unimolecular and to follow a first-order rate law. The products of elimination are acetone and acetaldehyde. The temperature dependence of the rate coefficients is expressed by the following equation: log[k1(s,1)],=,(13.05±0.53),(229.7±5.3),kJ,mol,1 (2.303RT),1. Theoretical estimations of the mechanism of this elimination suggest a molecular mechanism of a concerted non-synchronous four-membered cyclic transition-state process. An analysis of bond order and natural bond orbital charges suggests that the bond polarization of C(OH),C(O),, in the sense of C(OH),+&·C(O),,, is rate limiting in the elimination reaction. The rate coefficients obtained experimentally are in reasonably good agreement with the theoretical calculations. The mechanism of 3-hydroxy-3-methyl-2-butanone elimination is described. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Mechanism and structure,reactivity correlation in the homogeneous, unimolecular elimination kinetics of 2-substituted ethyl methylcarbonates in the gas phase

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 11 2003
Gabriel Chuchani
Abstract The gas-phase elimination kinetics of 2-substituted ethyl methylcarbonates were determined in a static reaction system over the temperature range of 323,435°C and pressure range 28.5,242 Torr. The reactions are homogeneous, unimolecular and follow a first-order rate law. The kinetic and thermodynamic parameters are reported. The 2-substituents of the ethyl methylcarbonate (CH3OCOOCH2CH2Z, Z=substituent) give an approximate linear correlation when using the Taft,Topsom method, log(kZ/kH)=,(0.57±0.19),,+(1.34±0.49),R, (r=0.9256; SD=0.16) at 400°C. This result implies the elimination process to be sensitive to steric factors, while the electronic effect is unimportant. However, the resonance factor has the greatest influence for a favorable abstraction of the ,-hydrogen of the C,,H bond by the oxygen carbonyl. Because ,, is significant, a good correlation of the alkyl substituents of carbonates with Hancock's steric parameters was obtained: log(kR/kH) versus ESC for CH3OCOOCH2CH2R at 400°C, R=alkyl, ,=,0.17 (r=0.9993, SD=0.01). An approximate straight line was obtained on plotting these data with the reported Hancock's correlation of 2-alkyl ethylacetates. This result leads to evidence for the ,-hydrogen abstraction by the oxygen carbonyl and not by the alkoxy oxygen at the opposite side of the carbonate. The carbonate decompostion is best described in terms of a concerted six-membered cyclic transition state type of mechanism. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Michaelis-Menten Elimination Kinetics of Acetaldehyde During Ethanol Oxidation

Dose,response feeding study of short chain chlorinated paraffins (SCCPs) in laying hens: Effects on laying performance and tissue distribution, accumulation and elimination kinetics

MOLECULAR NUTRITION & FOOD RESEARCH (FORMERLY NAHRUNG/FOOD), Issue 2 2007
Karl-Heinz Ueberschär
Abstract Technical short chain chlorinated paraffins (C10,C13 with 60% chlorine) were fed to 93 laying hens from 24 to 32 weeks of age in increasing concentrations of up to 100 mg/kg feed. No significant influence on health, relative organ weights or performance (laying intensity, egg weight, feed consumption) was noted. The chlorinated paraffin content of the tissues was linearly related to the concentration of short chain paraffins of the feed. The highest concentrations were found in abdominal fat, egg yolk and fatty tissues. Breast muscle, egg albumen and bile fluid contained minimal or no residues. Less than 1% of the chlorinated paraffins ingested were incorporated into the body (without head, feet, gut and feathers), whereas about 1.5% were eliminated with the egg yolk and 30% were excreted with urine and faeces. A six-week kinetic depuration study revealed a biphasic elimination with half-lifes of 4,40 min (liver, kidneys, legs, fat, blood) for the initial rapid phase, and 15,30 days (blood, fat, liver, yolk, kidneys, legs) for the terminal slow phase. [source]