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PubMed2005

Selective photocatalytic oxidation of light alkanes over alkali-ion-modified V2O5/SiO2; kinetic study and reaction mechanism.

Alkali-ion-modified silica-supported vanadium oxides are photocatalysts available in the field of photooxidation of light alkanes using molecular oxygen. The photooxygenated reaction was promoted over the catalyst under irradiation at steady state. Acetone formation on the photooxidation of propane was investigated over a rubidium-ion-modified silica-supported vanadium oxide that is the most effective catalyst. The kinetic analysis demonstrated that the rate-determining step is the reaction of propane on the lattice oxygen of the photoexcited VO4Rb species to yield the vanadium isopropoxide species. It was suggested that the photocatalytic active sites are occupied by photogenerated acetone during photoreaction at 333 K. Heating the photocatalyst bed drastically enhanced not only product yield but also the selectivity to propionaldehyde that is a minor product in the photooxidation at 333 K. The product distribution of photoassisted oxidation of propane was described by Boltzmann's distribution of stabilization energy of the intermediates: an isopropoxide-like one for the precursor of acetone and an n-propoxide-like one for the precursor of propionaldehyde.

Journal Article↗
PubMed2006

The surface chemistry of propylene, 1-iodopropane, and 1,3-diiodopropane on MoAl alloy thin films formed on dehydroxylated alumina.

The adsorption of C3 hydrocarbons propylene, 1-iodopropane, and 1,3-diiodopropane is studied in ultrahigh vacuum on a molybdenum-aluminum alloy formed by molybdenum hexacarbonyl reaction with a planar alumina film grown on a Mo(100) substrate. Carbon-iodine bond scission occurs below approximately 200 K to deposit iodine, and form propyl species from 1-iodopropane and a C3 metallacycle from 1,3-diiodopropane. Propyl species either undergo beta-hydride elimination to yield propylene or hydrogenate to form propane. Propylene adsorbs as both pi- and di-sigma-bonded species, and the di-sigma form hydrogenates to yield propane, where the addition of the first hydrogen to form propyl species is slower than the second hydrogenation step to yield propane. Propylene also thermally decomposes on the surface to desorb hydrogen and deposit carbon where the methylyne group is the most, and the methyl group the least reactive. The metallacyclic intermediate reacts to give an allylic intermediate, which forms propylene, but also decomposes by C-C bond cleavage to evolve ethylene and deposit methylene species on the surface. This is a key step in the mechanism proposed for heterogeneously catalyzed olefin metathesis and this is the first time that this chemistry has been directly identified in ultrahigh vacuum.

Journal Article↗
PubMed2006

Solvent effects on AOT reverse micelles in liquid and compressed alkanes investigated by neutron spin-echo spectroscopy.

Neutron Spin-Echo (NSE) spectroscopy has been employed to study the interfacial properties of reverse micelles formed with the common surfactant sodium bis-2-ethylhexyl-sulfosuccinate (AOT) in liquid alkane solvents and compressed propane. NSE spectroscopy provides a means to measure small energy transfers for incident neutrons that correspond to thermal fluctuations on the nanosecond time scale and has been applied to the study of colloidal systems. NSE offers the unique ability to perform dynamic measurements of thermally induced shape fluctuation in the AOT surfactant monolayer. This study investigates the effects of the bulk solvent properties, water content, and the addition of octanol cosurfactant on the bending elasticity of AOT reverse micelles and the reverse micelle dynamics. By altering these solvent properties, specific trends in the bending elasticity constant, k, are observed where increasing k corresponds to an increase in micelle rigidity and a decrease in intermicellar exchange rate, k(ex). The observed corresponding trends in k and k(ex) are significant in relating the dynamics of microemulsions and their application as a reaction media. Compressed propane was also examined for the first time with a high-pressure, compressible bulk solvent where variations in temperature and pressure are used to tune the properties of the bulk phase. A decrease in the bending elasticity is observed for the d-propane/AOT/W = 8 reverse micelle system by simultaneously increasing the temperature and pressure, maintaining constant density. With isopycnic conditions, a constant translational diffusion of the reverse micelles through the bulk phase is observed, conforming to the Stokes-Einstein relationship.

Journal Article↗
PubMed2006

Structures and reaction mechanisms of propene oxide isomerization on H-ZSM-5: an ONIOM study.

The isomerization mechanisms of propene oxide over H-ZSM-5 zeolite have been investigated via the utilization of 5T and 46T cluster models calculated by the B3LYP/6-31G(d,p) and the ONIOM(B3LYP/6-31G(d,p):UFF) methods, respectively. The reactions are considered to proceed through a stepwise mechanism: (1) the epoxide ring protonation, and concurrently the ring-opening, and (2) the 1,2-hydride shift forming the adsorbed carbonyl compound. Because of the asymmetric structure of propene oxide, two different C-O bonds (more or less substituted carbon atom sides) can be broken leading to two different types of products, propanal and propanone. The ring-opening step of these mechanisms is found to be the rate-determining step with an activation barrier of 38.5 kcal/mol for the propanal and of 42.4 kcal/mol for the propanone. Therefore, the propanal is predicted to be the main product for this reaction.

Journal Article↗
PubMed2001

Aromatase inhibitors from Broussonetia papyrifera.

Bioassay-guided fractionation of an ethyl acetate-soluble extract from the whole plants of Broussonetia papyrifera, using an in vitro aromatase inhibition assay, led to the isolation of five new active compounds, 5,7,2',4'-tetrahydroxy-3-geranylflavone (1), isogemichalcone C (8), 3'-[gamma-hydroxymethyl-(E)-gamma-methylallyl]-2,4,2',4'-tetrahydroxychalcone 11'-O-coumarate (9), demethylmoracin I (10), and (2S)-2',4'-dihydroxy-2' '-(1-hydroxy-1-methylethyl)dihydrofuro[2,3-h]flavanone (11), and 10 known (12-21) compounds which were also found to be active. Of these compounds, the most potent were 9 (IC(50) 0.5 microM), 11 (IC(50) 0.1 microM), isolicoflavonol (12, IC(50) 0.1 microM), and (2S)-abyssinone II (13, IC(50) 0.4 microM). Additionally, six new compounds, 5,7,3',4'-tetrahydroxy-6-geranylflavonol (2), 5,7,3',4'-tetrahydroxy-3-methoxy-6-geranylflavone (3), (2S)-7,4'-dihydroxy-3'-prenylflavan (4), 1-(2,4-dihydroxyphenyl)-3-(4-hydroxyphenyl)propane (5), 1-(2,4-dihydroxy-3-prenylphenyl)-3-(4-hydroxyphenyl)propane (6), and 1-(4-hydroxy-2-methoxyphenyl)-3-(4-hydroxy-3-prenylphenyl)propane (7), were isolated and characterized, but proved to be inactive as aromatase inhibitors, as were an additional 21 known compounds. The structures of the new compounds (1-11) were elucidated by spectroscopic methods. Structure-activity relationships in the aromatase assay were determined for the benzofurans, biphenylpropanoids, coumarins, and various types of flavonoids (chalcones, flavans, flavanones, and flavones) obtained among a total of 42 constituents of B. papyrifera.

Algorithms↗
PubMed2001

Synthesis of new carboxylesterase inhibitors and evaluation of potency and water solubility.

Carboxylesterases are essential enzymes in the hydrolysis and detoxification of numerous pharmaceuticals and pesticides. They are vital in mediating organophosphate toxicity and in activating many prodrugs such as the chemotherapeutic agent CPT-11. It is therefore important to study the catalytic mechanism responsible for carboxylesterase-induced hydrolysis, which can be accomplished through the use of potent and selective inhibitors. Trifluoromethyl ketone (TFK)-containing compounds are the most potent esterase inhibitors described to date. The inclusion of a thioether moiety beta to the carbonyl further increased TFK inhibitor potency. In this study, we have synthesized the sulfone analogues of a series of aliphatic and aromatic substituted thioether TFKs to evaluate their potency and solubility properties. This structural change shifted the keto/hydrate equilibrium from <9% hydrate to >95% hydrate, forming almost exclusively the gem-diol. These new compounds were evaluated for their inhibition of carboxylesterase activity in three different systems, rat liver microsomes, commercial porcine esterase, and juvenile hormone esterase in cabbage looper (Trichoplusia ni) hemolymph. The most potent inhibitor of rat liver carboxylesterase activity was 1,1,1-trifluoro-3-(decane-1-sulfonyl)-propan-2,2-diol, which inhibited 50% of the enzyme activity (IC(50)) at 6.3 +/- 1.3 nM and was 18-fold more potent than its thioether analogue. However, the sulfone derivatives were consistently poorer inhibitors of porcine carboxylesterase activity and juvenile hormone esterase activity, with IC(50) values ranging from low micromolar to millimolar. The compound 1,1,1-trifluoro-3-(octane-1-sulfonyl)-propan-2,2-diol was shown to have a 10-fold greater water solubility than its thioether analogue, 1,1,1-trifluoro-3-octylsulfanyl-propan-2-one (OTFP). These novel compounds provide further evidence of the differences between esterase orthologs, suggesting that additional development of esterase inhibitors may ultimately provide a battery of ortholog and/or isoform selective inhibitors analogous to those available for other complex enzyme families with overlapping substrate specificity.

Animals↗
PubMed1992

Solubilization and activity of proteins in compressible-fluid based microemulsions.

We have used the pressure dependency of density in near critical propane to design a novel protein extraction system. Active, structurally intact, proteins have been extracted from an aqueous phase into subcritical propane containing the non-ionic detergent polyoxyethylene sorbitan trioleate (Tween-85). The pressure dependence of protein transfer from the aqueous to organic phase is described for cytochrome C and subtilisin. The effect of the microemulsion and compressible propane on protein structure and function is also discussed. The first determinations of kinetic constants for an enzyme-catalyzed reaction in such a system are also presented.

Cytochrome c Group↗
PubMed2001

Cyclodextrin derivative-coated quartz crystal microbalances for alcohol sensing and application as methanol sensors.

Three novel cyclodextrin derivatives, mono(6-benzylimino-6-deoxy)-beta-cyclodextrin (2), mono-(6-cyclohexylamino-6-deoxy)-beta-cyclodextrin (3) and mono(6-benzylamino-6-deoxy)-beta-cyclodextrin (4), together with mono(6-phenylamino-6-deoxy)-beta-cyclodextrin (1), were synthesized and employed as sensing materials coated on quartz crystal microbalances (QCMs). Comparison of the responses to some alcohol and solvent vapours such as methanol, ethanol, propan-1-ol, propan-2-ol, butan-1-ol, acetone, chloroform and benzene indicated that these beta-cyclodextrin derivatives show considerable sensitivity and selectivity towards methanol. It shows a good linear relationship between the frequency shift and the methanol concentration in the range 3-160 mg L(-1) for 2-4 and 3-140 mg L(-1) for 1. The correlation coefficients are 0.9971, 0.9983, 0.9973 and 0.9977, respectively. The limit of detection (LOD) is 0.2 mg L(-1). When small amounts of other vapours co-exist, e.g., ethanol, propan-1-ol and acetone, the responses differ from that of pure methanol vapour, and a deduction method could eliminate this cross-sensitivity. The water cross-sensitivity was very low. These QCMs coated with cyclodextrin derivatives are employed as methanol sensors in the real atmosphere to detect on-line the concentration of methanol vapour.

Air Pollutants, Occupational↗
PubMed2006

Use of the tetrahydroborate ligand as "gate-keeper" and protected hydride ligand: preparation and study of alkyl hydride and acyl hydride complexes of ruthenium(II).

Complex 3, [Ru(eta2-BH4)(CO)(Et)L2] (L = PMe2Ph) can be converted by nucleophiles L' {a, PMe2Ph; b, P(OMe)3; c, Me3CNC; d, CO} to alkyl and acyl complexes [Ru(eta1-BH4)(CO)(Et)L2L'] (4a), [Ru(eta2-BH4)(COEt)L2L'] (5a-d), and [Ru(eta1-BH4)(COEt)L2L'2] (7d and isomers 7c and 10c). Deprotection can then be achieved under conditions mild enough to allow study of the resulting alkyl hydride complexes [Ru(CO)(Et)HL2L'] (1a, 1b) and acyl hydride complexes [Ru(COEt)HL2L'2] (8c, 8d) prior to elimination of ethane and propanal respectively, with formation of ruthenium(0) complexes [Ru(CO)L2L'2] (6a, 6b, 6d). With Me3CNC, however, the final product is (depending on the solvent used) [Ru(CNCMe3)2{C(H)NCMe3}(COEt)L2] (9c) or [Ru(CNCMe3)3(COEt)L2]+ (11c). Successive treatment of [Ru(eta2-BH4)(CO)HL2], , with ethene and then CO yields propanal, but turning this into a catalytic cycle is hindered by the greater readiness of to yield propanal non-catalytically (reacting with CO) than catalytically (reacting with H2).

Journal Article↗
PubMed1996

Cloning and expression of the gene encoding the Thermoanaerobacter ethanolicus 39E secondary-alcohol dehydrogenase and biochemical characterization of the enzyme.

The adhB gene encoding Thermoanaerobacter ethanolicus 39E secondary-alcohol dehydrogenase (S-ADH) was cloned, sequenced and expressed in Escherichia coli. The 1056 bp gene encodes a homotetrameric recombinant enzyme consisting of 37.7 kDa subunits. The purified recombinant enzyme is optimally active above 90 degrees C with a half-life of approx. 1.7 h at 90 degrees C. An NADP(H)-dependent enzyme, the recombinant S-ADH has 1400-fold greater catalytic efficiency in propan-2-ol oxidation than in ethanol oxidation. The enzyme was inactivated by chemical modification with dithionitrobenzoate (DTNB) and diethylpyrocarbonate, indicating that Cys and His residues are involved in catalysis. Zinc was the only metal enhancing S-ADH reactivation after DTNB modification, implicating the involvement of bound zinc in catalysis. Arrhenius plots for the oxidation of propan-2-ol by the native and recombinant S-ADHs were linear from 25 to 90 degrees C when the enzymes were incubated at 55 degrees C before assay. Discontinuities in the Arrhenius plots for propan-2-ol and ethanol oxidations were observed, however, when the enzymes were preincubated at 0 or 25 degrees C. The observed Arrhenius discontinuity therefore resulted from a temperature-dependent, catalytically significant S-ADH structural change. Hydrophobic cluster analysis comparisons of both mesophilic and thermophilic S-ADH and primary- versus S-ADH amino acid sequences were performed. These comparisons predicted that specific proline residues might contribute to S-ADH thermostability and thermophilicity, and that the catalytic Zn ligands are different in primary-alcohol dehydrogenases (two Cys and a His) and S-ADHs (Cys, His, and Asp).

Alcohol Dehydrogenase↗
PubMed2005

C-H activation of alkanes on Rh+ n (n=1-30) clusters: size effects on dehydrogenation.

The rate coefficients for the dehydrogenation of ethane, propane, and isobutane with cationic rhodium atoms Rh+ and clusters Rh+ n of up to 30 atoms were measured under single-collision conditions in a Fourier-transform ion cyclotron resonance mass spectrometer. The reaction rates are cluster size dependent and parallel for all the three alkanes. While the reactions proceed close to the theoretical collision rates for a large number of clusters, characteristic minima are observed for Rh+ (5/6/9/19/28). The degree of dehydrogenation varies with the cluster size with maxima for 10< or =n< or =15 for the three alkanes and for n=3 and 2-4 in the cases of ethane and propane, respectively. However, complete dehydrogenation is only observed for the reaction of Rh+ 11 with propane. Dehydrogenation is remarkably selective and no other neutral products than H2 are observed. The results are interpreted in terms of likely cluster geometries.

Journal Article↗
PubMed2006

Estimated MP2 and CCSD(T) interaction energies of n-alkane dimers at the basis set limit: comparison of the methods of Helgaker et al. and Feller.

The MP2 (the second-order Møller-Plesset calculation) and CCSD(T) (coupled cluster calculation with single and double substitutions with noniterative triple excitations) interaction energies of all-trans n-alkane dimers were calculated using Dunning's [J. Chem. Phys. 90, 1007 (1989)] correlation consistent basis sets. The estimated MP2 interaction energies of methane, ethane, and propane dimers at the basis set limit [EMP2(limit)] by the method of Helgaker et al. [J. Chem. Phys. 106, 9639 (1997)] from the MP2/aug-cc-pVXZ (X=D and T) level interaction energies are very close to those estimated from the MP2/aug-cc-pVXZ (X=T and Q) level interaction energies. The estimated EMP2(limit) values of n-butane to n-heptane dimers from the MP2/cc-pVXZ (X=D and T) level interaction energies are very close to those from the MP2/aug-cc-pVXZ (X=D and T) ones. The EMP2(limit) values estimated by Feller's [J. Chem. Phys. 96, 6104 (1992)] method from the MP2/cc-pVXZ (X=D, T, and Q) level interaction energies are close to those estimated by the method of Helgaker et al. from the MP2/cc-pVXZ (X=T and Q) ones. The estimated EMP2(limit) values by the method of Helgaker et al. using the aug-cc-pVXZ (X=D and T) are close to these values. The estimated EMP2(limit) of the methane, ethane, propane, n-butane, n-pentane, n-hexane, n-heptane, n-octane, n-nonane, and n-decane dimers by the method of Helgaker et al. are -0.48, -1.35, -2.08, -2.97, -3.92, -4.91, -5.96, -6.68, -7.75, and -8.75 kcal/mol, respectively. Effects of electron correlation beyond MP2 are not large. The estimated CCSD(T) interaction energies of the methane, ethane, propane, and n-butane dimers at the basis set limit by the method of Helgaker et al. (-0.41, -1.22, -1.87, and -2.74 kcal/mol, respectively) from the CCSD(T)/cc-pVXZ (X=D and T) level interaction energies are close to the EMP2(limit) obtained using the same basis sets. The estimated EMP2(limit) values of the ten dimers were fitted to the form m0+m1X (X is 1 for methane, 2 for ethane, etc.). The obtained m0 and m1 (0.595 and -0.926 kcal/mol) show that the interactions between long n-alkane chains are significant. Analysis of basis set effects shows that cc-pVXZ (X=T, Q, or 5), aug-cc-pVXZ (X=D, T, Q, or 5) basis set, or 6-311G** basis set augmented with diffuse polarization function is necessary for quantitative evaluation of the interaction energies between n-alkane chains.

Journal Article↗
PubMed2004

Development of an analytical method for 3-monochloropropane-1,2-diol in soy sauce using 4-heptanone as derivatizing agent.

3-Monochloro-1,2-propane diol is a suspected carcinogen found in hydrolysed vegetable protein products such as soy sauce. A method is described for the analysis of 3-monochloro-1,2-propane diol in soy sauce by gas chromatography-mass spectrometry at a concentration range of 1-5000 ng g-1 using 4-heptanone as the derivatizing ketone and 3-monochloro-1,2-propane diol-d5 as the internal standard. The limit of detection for the method in the soy sauce matrix was 0.48 ng g-1 and the limit of quantification was 1.2 ng g-1.

Carcinogens, Environmental↗
PubMed1998

Radon-222 and gamma ray levels associated with the collection, processing, transmission, and utilization of natural gas.

The natural gas industry in British Columbia was investigated for exposure to radioactive contaminants such as radon-222 and lead-210. Radon activity associated with the gathering system ranged from 7-921 Bq/m3. The pipelines to the processing facility contained sludge that had a mean lead-210 activity of 0.494 Bq/g (0.379 standard deviation [SD]) and a mean radium-226 activity of 0.417 (0.398 SD). Within the processing facility the highest levels of radon were associated with propane production streams, and activities as high as 4958 Bq/m3 were found. Equipment handling these streams was also found to have a buildup of scale with lead-210, radium-224, and radium-226 activity. The transmission of salable gas to the consumer indicated a decrease in radon activity that was slightly lower than the estimated radon activity based on the half-life of radon, the distance from the production facility, and the speed of gas transmission. The risk of radon exposure to the worker was deemed well below the guidelines and would be controlled more than adequately by means of the occupational standards for the natural gas components. Gamma ray exposure was also well below the occupational standards. Radon exposure to the consumer was virtually nonexistent in the Vancouver region from both natural gas and propane. Although this might not be the case for consumers of propane closer to the production facilities, its contribution is likely to be minimal.

British Columbia↗
PubMed2001

Determination of aldehydes in fish by high-performance liquid chromatography.

A new analytical method to determine trace volatile aldehydes isolated from the headspace of fish meat at room temperature by high-performance liquid chromatography (HPLC) in the form of 2,4-dinitrophenylhydrazone (DNPHo) derivatives has been developed. Aliquots (50 g) of the fish purée were introduced into a 500-mL glass recipient and were purged with N2 for 40 min through two SEP-PAK C18 cartridges (connected in series) coated with an acid solution of 2,4-dinitrophenylhydrazine. The cartridges were then eluted with acetonitrile (2 mL) and the 2,4-DNPHo formed was quantitated by HPLC-UV analysis using a Zorbax C18 column. The isolated compounds from the dynamic headspace sampling of four kinds of fish species were saturated aldehydes, formaldehyde, acetaldehyde, propanal, butanal, pentanal, and hexanal. Under optimized conditions the detection limits of the HPLC method were in the range of 0.75 nmol/g (formaldehyde) to 2.19 nmol/g (hexanal). The calibration curves were linear in the concentration range from 1.3 nmol/mL to 12.5 nmol/mL. Propanal and acetaldehyde were the major carbonyl compounds identified (ranging from 3.9 nmol/g and 10 nmol/g). This study has revealed the widespread occurrence of formaldehyde, acetaldehyde, propanal, butanal, pentanal, and hexanal in fish meat.

Aldehydes↗
PubMed2004

Experimental equivalent cluster-size distributions in nanometric volumes of liquid water.

Ionisation cluster-size distributions in nanometric volumes of liquid water were determined for alpha particles at 4.6 and 5.4 MeV by measuring cluster-size frequencies in small gaseous volumes of nitrogen or propane at low gas pressure as well as by applying a suitable scaling procedure. This scaling procedure was based on the mean free ionisation lengths of alpha particles in water and in the gases measured. For validation, the measurements of cluster sizes in gaseous volumes and the cluster-size formation in volumes of liquid water of equivalent size were simulated by Monte Carlo methods. The experimental water-equivalent cluster-size distributions in nitrogen and propane are compared with those in liquid water and show that cluster-size formation by alpha particles in nitrogen or propane can directly be related to those in liquid water.

Algorithms↗
PubMed1999

Biotransformation and kinetics of excretion of methyl-tert-butyl ether in rats and humans.

Methyl-tert-butyl ether (MTBE) is widely used as an additive to gasoline to increase oxygen content and reduce tail pipe emission of pollutants. Therefore, widespread human exposure may occur. To contribute to the characterization of potential adverse effects of MTBE, its biotransformation was compared in humans and rats after inhalation exposure. Human volunteers (3 males and 3 females) and rats (5 each, males and females) were exposed to 4 (4.5 +/- 0.4) and 40 (38.7 +/- 3.2) ppm MTBE for 4 h in a dynamic exposure system. Urine samples from rats and humans were collected for 72 h in 6-h intervals, and blood samples were taken in regular intervals for 48 h. In urine, MTBE and the MTBE metabolites tertiary-butanol (t-butanol), 2-methyl-1,2-propane diol, and 2-hydroxyisobutyrate were quantified; MTBE and t-butanol were determined in blood samples. After the end of the exposure period, inhalation of 40 ppm MTBE resulted in blood concentrations of MTBE 5.9 +/- 1.8 microM in rats and 6.7 +/- 1.6 microM in humans. The MTBE blood concentrations after inhalation of 4 ppm MTBE were 2.3 +/- 1.0 in rats and 1.9 +/- 0.4 microM in humans. MTBE was rapidly cleared from blood with a half-life of 2.6 +/- 0.9 h in humans and 0.5 +/- 0.2 h in rats. The blood concentrations of t-butanol were 21.8 +/- 3.7 microM in humans and 36.7 +/- 10.8 microM in rats after 40 ppm MTBE, and 2.6 +/- 0.3 in humans and 2.9 +/- 0.5 in rats after 4 ppm MTBE. In humans, t-butanol was cleared from blood with a half-life of 5.3 +/- 2.1 h. In urine samples from controls and in samples collected from the volunteers and rats before the exposure, low concentrations of t-butanol, 2-methyl-1,2-propane diol and 2-hydroxyisobutyrate were present. In urine of both humans and rats exposed to MTBE, the concentrations of these compounds were significantly increased. 2-Hydroxyisobutyrate was recovered as a major excretory product in urine; t-butanol and 2-methyl-1,2-propane diol were minor metabolites. All metabolites of MTBE excreted with urine were rapidly eliminated in both species after the end of the MTBE exposure. Elimination half-lives for the different urinary metabolites of MTBE were between 7.8 and 17.0 h in humans and 2.9 to 5.0 h in rats. The obtained data indicate that MTBE biotransformation and excretion are similar in rats and humans, and MTBE and its metabolites are rapidly excreted in both species. Between 35 and 69% of the MTBE retained after the end of the exposure was recovered as metabolites in urine of both humans and rats.

Adult↗
PubMed2000

Biotransformation and kinetics of excretion of ethyl tert-butyl ether in rats and humans.

Ethyl tert-butyl ether (ETBE) may be used in the future as an additive to gasoline to increase oxygen content and reduce tailpipe emissions of pollutants. Therefore, widespread human exposure may occur. To contribute to the characterization of potential adverse effects of ETBE, its biotransformation was compared in humans and rats after inhalation exposure. Human volunteers (3 males and 3 females) and rats (5 males and 5 females) were exposed to 4 (4.5+/-0.6) and 40 (40.6+/-3.0) ppm ETBE for 4 h in a dynamic exposure system. Urine samples from rats and humans were collected for 72 h at 6-h intervals, and blood samples were taken in regular intervals for 48 h. In urine, ETBE and the ETBE-metabolites tert-butanol (t-butanol), 2-methyl-1,2-propane diol, and 2-hydroxyisobutyrate were quantified; ETBE and t-butanol were determined in blood samples. After the end of the exposure period to inhalation of 40-ppm ETBE, blood concentrations of ETBE were found at 5.3+/-1.2 microM in rats and 12.1+/-4.0 microM in humans. The ETBE blood concentrations, after inhalation of 4-ppm ETBE, were 1.0+/-0.7 microM in rats and 1.3+/-0.7 microM in humans. ETBE was rapidly cleared from blood. After the end of the 40-ppm ETBE exposure period, the blood concentrations of t-butanol were 13.9+/-2.2 microM in humans and 21.7+/-4.9 microM in rats. After 4-ppm ETBE exposure, blood concentrations of t-butanol were 1.8+/-0.2 microM in humans and 5.7+/-0.8 microM in rats. t-Butanol was cleared from human blood with a half-life of 9.8+/-1.4 h in humans after 40-ppm ETBE exposure. In urine samples from controls and in samples collected from the volunteers and rats before the exposure, low concentrations of t-butanol, 2-methyl-1,2-propane diol, and 2-hydroxyisobutyrate were present. In the urine of both humans and rats exposed to ETBE, the concentrations of these compounds were significantly increased. 2-Hydroxy-isobutyrate was recovered in urine as the major excretory product formed from ETBE; t-butanol and 2-methyl-1,2-propane diol were minor metabolites. All metabolites of ETBE excreted with urine were rapidly eliminated in both species after the end of the ETBE exposure. Excretion half-lives for the different urinary metabolites of ETBE were between 10.2 and 28.3 h in humans and 2.6 and 4.7 h in rats. The obtained data indicate that ETBE biotransformation and excretion are similar for rats and humans, and that ETBE and its metabolites are rapidly excreted by both species. Between 41 and 53% of the ETBE retained after the end of the exposure was recovered as metabolites in the urine of both humans and rats.

Administration, Inhalation↗