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BACKGROUND: Computational modeling of the absorption, distribution, metabolism, and excretion of chemicals is now theoretically able to describe metabolic interactions in realistic mixtures of tens to hundreds of substances. That [...]

The absolute absorption spectrum of the benzyl radical in the visible region measured by ring-down spectroscopy in the visible region measured by cavity ring-down spectroscopy is presented. The absorption cross sections reported would facilitate the quantification of the benzyl radical in future kinetic studies.

ABSTRACT Stenotrophomonas maltophilia T3-c, isolated from a biofilter for the removal of benzene, toluene, ethylbenzene, and xylene (BTEX), could grow in a mineral salt medium containing toluene, benzene, or ethylbenzene [...]

BTEX and two chemical warfare simulants, half mustard and dissopropylmethyl phosphonate, are placed in water and adsorbed into fiberglass supported activated carbon filters. Removal of the contaminants, the pressure drops of the filters, and the regeneration of the FGAC filter is graphed.

Theoretical and experimental investigations have been conducted on the adsorption characteristics of benzene, toluene, ethylbenzene, and xylene (BTEX) by macroreticular resins. A theoretical model is proposed for describing the BTEX breakthrough curves of the adsorption column. The column adsorption model contains two model parameters, (tau) and (Kappa), that are conveniently estimated using the observed breakthrough data. The model was tested for benzene adsorption with a flow rate between 12 and 30 mL/min, inlet concentration between 200 and 500 mg/L, and temperature between 30 and 60 degrees C. Excellent fit of the model to the measured data was obtained. The proposed model hence offers a convenient means for accurate predictions of the adsorption capacity and breakthrough point of a column BTEX adsorption process. Also developed are the mass balance equations representing countercurrent multistage adsorption process. The countercurrent multistage adsorption process has been shown to save a significant amount of adsorption resin in achieving the same BTEX removal as the single-stage process. Experimental tests for a two-stage example verify that up to 60% of the Ambersorb resin can be saved over a single-stage process.

A 2H NMR study on clathrates with a polycyano-polycadmate host is presented. A number of models of guest molecular motions are suggested based on their molecular and crystal structures.

Experiments on the absorption of toluene, 0-xylene and benzene to wood are described. The results could be used to help predict organic contaminant transport at landfills, which often contain up to 25% wood waste by weight.

Systematic X-ray structural research was conducted on new weak complexes of Fe(TPP)+ with arenes and with C60 along with measurements using nonlocal density functional theory. The result establishes a covalent component to the weak binding of arenes to iron(III) porphyrin cations. It suggests that solventss such as benzene must be considered as potential ligands in any situation where coordinatively unsaturated cations are generated.

Nitrosation by NO+ of benzene and toluene proceeds through initial formation of intermediate electron donor-acceptor pi-complexes. This was confirmed by ab initio molecular orbital and B3LYP hybrid Hartree-Fock/density-functional calculations in a computational study of the roles of pi- and sigma-complexes, especially their electron donor-acceptor character, in such aromatic nitrosations. Results showed good agreement between calculated pi-complex geometries and energies and experimental data.

Electron spin resonance (ESR) spectroscopy and electron nuclear double resonance resonance (ENDOR) spectroscopy are used to examine the radical cations of methyl-substituted benzene generated in halocarbon matrices by X-ray irradiation at 77 K. Results of the ESR and ENDOR spectroscopy show that radical cations are dominated by large axially symmetric hyperfine splitting due to methyl-group protons. Experimental and theoretical evidence also showed that radical cations of toluene and p-xylene had a more stable type of state than o-xylene and m-xylene.

A study was conducted to analyze the metabolism of benzene, toluene and xylene (BTX) hydrocarbons in soil. Microtox toxicity assays were carried out on extracts of soil samples incubated with benzene, toluene and p-xylene mixtures. Total radiocarbon bound in the soil was then obtained using the web combustion of soil samples. Results indicated that xylenes are cometabolized in BTX mixtures applied to soil before being mineralized because of the diversity of soil microorganisms.

Benzene, toluene and binary mixtures of these molecules in the gas phase are studied using femtosecond time-resolved anti-Stokes Raman scattering (CARS). Results show that the CARS signal indicates no oscillatory patterns and decays for benzene while temporal variations reflecting the vibrational periods of the system are observed for toluene. For benzene and toluene mixtures, a strong oscillation in the transient signal corresponding to a beat between the vibrational mode in the benzene and toluene is found.

A study was conducted to analyze the structural transformations of the C70 in benzene, toluene, and hexane solutions using x-ray powder diffraction techniques. The crystals were prepared from a benzene solution by slow evaporation. The Siemens D5000 diffractometer was utilized to carry out the x-ray diffraction experiments. Results indicated an orthorhombic structure for low-temperature phase and a mixture of a monoclinic phase supporting pure hcpI phase for high temperature.

The free energy dependence on the fluorescence quenching of 2,4,6-triphenylthiopyrylium tetrafluoroborate (TPTP) by a number of halogenated benzenes, toluenes and anisoles, was investigated in acetonitrile. The radical yield and intersystem-crossing rate constants were analyzed through flash photolysis methods. The effect of the sulfur atom on the triplet induction was indicated in the intersystem-crossing rate constant and radical yield values.

Stable carbon isotopic analysis is an ideal tool for the remediation of contaminants such as benzene, toluene, ethylbenzene and xylenes (BETX). The process was effective in determining the concentrations and stable isotope values of BETX at a gasoline-contaminated site in southern California. The method, whereby purge-and-trap is connected to a gas chromatograph/ion trap mass spectrometer system, yielded varying concentrations of BETX that range from below detectable to highly detectable levels. Results indicate that toluene usually yield the highest concentrations.

Introduction Contamination of ground-water supplies by gasoline and other petroleum-derived hydrocarbons released from underground storage tanks (USTs) is a serious and widespread environmental problem. Corrosion, ground movement, and poor sealing [...]

Free energy simulations were performed to determine the relative orientational preference of benzene and toluene molecules in water and in a vacuum. The molecules studied include face-to-face stacked, point-to-face T-shaped and orientationally averaged toluene and benzene homodimers. The results demonstrated the pi-pi interactions in both lead to different orientational preferences. As such, the use of toluene to model the phenylalanine side chain of proteins is not a good idea.

Previous research has shown that dimers of the type R2-NM(mu-NR2)2MNR2 are formed in the solvent-free homoleptic bis(trimethylsilyl)amides of calcium, strontium and barium in solution and the solid state. Whether this is also true in benzene or toluene solutions remain unknown. To resolve this problem, dimers in a toluene solution are investigated. Results indicate that a bicyclic dimer with the same moiety as those in calcium, strontium and barium exists in toluene solution. Also shown is a crystalline state for a barium diphospholanide.

Radiolytic experiments on the gas-phase reactions of free Me3C+ and Me3Si+ cations with benzene and toluene determined the kinetic formation and mechanistic role of ipso-substituted arenium ions. Analysis of the 1,2-H(D) shifts confirmed the intermediacy of the gaseous arenium ions. Additional reactivity studies involving competitive tert-butylation processes further characterized the nature of the gas-phase aromatic substitution.

An atmospheric pressure ionization (API) source used with tandem mass spectrometry is effective in measuring dilute hydrocarbons in automobile exhaust. An API source and a triple quadrupole spectrometer can measure benzene and toluene at real-time rates as high as 100 hertz. In contrast, a low-pressure chemical ionization source used with tandem mass spectrometry is less sensitive than the API source method.

Research was conducted to examine the hypothesis that Al(C6F5)3 might coordinate to arenes in a manner that is similar to that of (SiEt3)+. The anaerobic reactions of B(C6F5)3 and AlMe3 in either toluene or benzene solutions at 25 degrees C for 12 h were investigated. The resulting single crystals of Al(C6F5)3*benzene and Al(C6F5)3*toluene had filtrate concentrations that were suitable for analysis by means of X-ray diffraction. Results indicate the sequence of donor strengths, THF > benzene > et2O toward Al(C6F5)3.

Further evidence have been obtained for the intermediacy of inert-molecule-separated ion pairs in deamination. These include the insensitivity of the cation to the nucleophilicity of the counterion, the temperature dependence of the yield of ester and the production of higher yields of solvent-derived products when N2O is generated as the inert molecule. Similarities in product distribution were seen for the benzylation of benzene-toluene mixtures using nitrosoamides, nitroamides, phenyldiazomethane and a hydroxylamine.

Mineralisation rates for ring-labelled [sup.14]C-atrazine, benzene, and toluene were determined for a number of Swan Coastal Plain soils which had not been previously in contact with these contaminants. Microbial biomass was estimated by phospholipid techniques in soil samples from the same sites. Mineralisation rates for the volatile aromatic hydrocarbons in the thin (up to 30 cm) surface soils (23.4-42.6 µmol/kg.day when fitted to zeroth-order rate kinetics) were appreciably faster than the mineralisation rates measured in soils collected from a depth of 1 m (0.11-3.0 µmol/kg.day). The pesticide atrazine was degraded slowly, with degradation rates in surface soils ranging from 1.22x[10.sup.-3] to 2.78x[10.sup.-4] µmol/kg.day, and those in soils at 1 m ranging from 5.13x[10.sup.-4] to 3.16x[10.sup.-4] µmol/kg.day. When mineralisation data were fitted to first-order kinetics then half-lives for atrazine mineralisation ranged from about 1 year in surface soils to 3.1-5.1 years in soils at 1 m. These rates were comparable to atrazine mineralisation rates measured in soils that had not been previously in contact with atrazine, as reported by others. The extent of mineralisation of the organic compounds v. time generally fitted better to zeroth-order kinetics than to first-order kinetics. Confidence in the determination of the mineralisation rate at slow rates of mineralisation was low ([r.sup.2] as low as 0.2 in plots of the extent of mineralisation v. time in zeroth-order and first-order plots for samples that showed slow mineralisation). Biomass, expressed as stationary phase Escherichia coli equivalents (SPEE), ranged from 1.4x[10.sup.7] to 1.2x[10.sup.8] SPEE/g dry weight for surface soils, and from 8.6x[10.sup.5] to 7.3x[10.sup.6] SPEE/g dry weight for soils at 1 m. The phospholipids extracted from surface soils tended to contain higher proportions of unsaturated and hydroxy fatty acids than soils at 1 m, which contained higher relative concentrations of branched fatty acids, which is consistent with the microbiota moving, with greater depth, from a Gram-negative to a more Gram-positive dominated population. Biomass correlated well with mineralisation rates of the volatile aromatic compounds ([r.sup.2] = 0.96) but less so with atrazine mineralisation rates ([r.sup.2]= 0.86), although further experiments would be required to determine if biomass was consistently a good predictor of mineralisation rate for these organic contaminants. The results suggest that it is important to maintain a fertile, `microbially rich' soil in order to maximise the potential for mineralisation of organic contaminants above groundwater resources. The mineralisation rate measurements for atrazine obtained in this study should be useful in models for the prediction of the contamination threat to groundwater resources. Additional keywords: atrazine mineralisation, benzene mineralisation, phospholipids., Introduction Pesticides and other organic compounds are regularly applied to soil surfaces, either purposefully or through accidental release. In a survey in 1990 for pesticide residues of US groundwater, 10.5% [...]