Reductive cleavage of 2,2,2-trichloroethyl esters by titanocene catalysis.

Esters are of widespread use for protecting carboxylic acids in organic synthesis. However, methods to cleave esters often employ harsh conditions. Herein, we report a new and mild method for the reductive cleavage of 2,2,2-trichloroethylesters (TCE esters). Our radical method employs Cp(2)TiCl as an electron transfer catalyst and Zn dust as stoichiometric reducing agent. It avoids the use of strong Brønstedt-acids as well as aqueous conditions and can be carried out at room temperature.

Covalent interaction of metabolites of the carcinogen trichloroethylene in rat hepatic microsomes.

Trichloroethylene (TCE), a structural analog of vinyl chloride, is known to induce hepatocellular carcinoma and other tumors in C57BL/6 X C3H/He F1 (hereafter known as B6C3F1) hybrid mice. TCE epoxide, a possible metabolite, is expected to be highly reactive toward cellular nucleophiles, e.g., proteins and nucleic acids. Hence, the microsomal metabolism of TCE and its covalent binding to microsomal protein were examined. Rat liver microsomes were incubated in vitro with [14C]TCE. The results showed that TCE binds covalently to microsomal protein since extensive organic extractions and Pronase digestion do not dissociate the TCE-protein complex. The binding was decreased by 7,8-benzoflavone, blocked by SKF-525A, and enhanced by i.p. administration of phenobarbital. The possibility that TCE epoxide, once formed, could be converted to water-soluble products through enzymatic hydrolysis by epoxide hydrase was also investigated. Addition of 3,3,3-trichloropropene oxide, a potent inhibitor of epoxide hydrase, to the incubation system markedly enhanced the binding of TCE. These observations support the view that, in order to bind to protein, it is necessary for TCE to be metabolized to its epoxide, a reactive intermediate that is most likely involved in TCE carcinogenesis and toxicity.

4-amino-6-(trichloroethenyl)-1,3-benzenedisulfonamide, a new, potent fasciolicide.

The synthesis and fasciolicidal activity of 4-amino-6-(trichloroethenyl)-1,3-benzenedisulfonamide are reported. A single dose of 15 mg/kg was effective in removing over 90% of immature Fasciola hepatica from sheep (6 weeks after infection) and calves (8 weeks after infection). A 2.5 mg/kg dose removed over 90% of mature (16 weeks old) liver fluke from sheep. Single oral doses up to 400 mg/kg were tolerated by sheep without gross toxic symptoms.

Mutagenicity of the glutathione and cysteine S-conjugates of the haloalkenes 1,1,2-trichloro-3,3,3-trifluoro-1-propene and trichlorofluoroethene in the Ames test in comparison with the tetrachloroethene-analogues.

The nephrotoxic and nephrocarcinogenic potential of the haloalkenes is associated with the conjugation of the chemicals to L-glutathione. Subsequent processing of the haloalkene glutathione S-conjugates via the cysteine conjugate beta-lyase pathway in the mammalian kidney yields nephrotoxic and mutagenic species. To investigate whether S-conjugates of the model chlorofluoroalkenes 1,1,2-trichloro-3,3,3-trifluoro-1-propene (CAS # 431-52-7) and trichlorofluoroethene (CAS # 359-29-5) show comparable effects, we have synthesised the respective cysteine and glutathione S-conjugates and subjected them to the Ames test. The cysteine and glutathione S-conjugates of tetrachloroethene (CAS # 127-18-4), S-(1,2,2-trichlorovinyl)-L-cysteine (TCVC) and S-(1,2,2-trichlorovinyl)glutathione (TCVG) were used as positive controls and reference substances. S-(1,2-dichloro-3,3,3-trifluoro-1-propenyl)-L-cysteine (DCTFPC) and S-(2,2-dichloro-1-fluorovinyl)-L-cysteine (DCFVC) showed clear dose-dependent mutagenic effects with the Salmonella typhimurium tester strains TA100 and TA98. Using TCVC as a reference substance the following ranking in mutagenic response was established: TCVC>DCTFPC>DCFVC. S-(1,2-dichloro-3,3,3-trifluoro-1-propenyl)glutathione (DCTFPG) and S-(2,2-dichloro-1-fluorovinyl)glutathione (DCFVG) showed potent dose-dependent mutagenic effects with the S. typhimurium tester strain TA100 in the presence of a rat kidney S9-protein fraction; tests carried out in the absence of the bioactivation system resulted only in background rates of revertants. Using TCVG as a reference substance the following ranking in mutagenic response was established: TCVG=DCTFPG>DCFVG. The data obtained provide a basis for further studies on the mutagenic and presumable carcinogenic potential of the substances.

Trichloroethylene. III. Prediction of carcinogenicity of investigated compounds including trichloroethylene.

The mutagenicity and carcinogenic properties of trichloroethylene (TCE) derivatives, and their correlation with its molecular properties were analyzed. The observed cancer incidence was compared to the predicted, calculated incidence. The predictions were based on the rodent bioassay results and were consistent with human data. The electrophilic data of molecules of the Ke system provided evidence for 205 rodent carcinogens, where Ke correlated with energy of the lowest unoccupied molecular orbital. The majority of carcinogenic compounds were found to be electron acceptors with decreased lowest unoccupied molecular orbital (LUMO) energy, indicating the particular DNA-reactivity leading to mutations and abnormal cell division. Based on the mutagenic activity in Ames test, the affinity of target organs for mutagens and non mutagens were compared in 351 rodent carcinogens. Nearly 80% of carcinogens (mutagenic and non mutagenic ones) were positive in the mouse and rat, in at least one of the most frequent target organs, i.e. liver, lung, mammary gland, stomach, kidney, hematopoietic system, urinary bladder and vascular system. Several predictive methods have been developed over the last 5 years based on structure-activity relationship studies known as US National Toxicology Program. One of these programs, called "PROGOL" is widely used for the prediction of carcinogenesis for a wide variety of compounds, e.g., nitro aromatics and suramin analogs. This program provides a simple model for predictive carcinogenesis, despite of the fact that the very first steps of carcinogenesis are not fully understood yet.

Biofiltration of trichloroethylene-contaminated air: a pilot study.

This project demonstrated the biofiltration of a trichloroethylene (TCE)-contaminated airstream generated by air stripping groundwater obtained from several wells located at the Anniston Army Depot, Anniston, AL. The effects of several critical process variables were investigated to evaluate technical and economic feasibility, define operating limits and preferred operating conditions, and develop design information for a full-scale biofilter system. Long-term operation of the demonstration biofilter system was conducted to evaluate the performance and reliability of the system under variable weather conditions. Propane was used as the primary substrate necessary to induce the production of a nonspecific oxygenase. Results indicated that the process scheme used to introduce propane into the biofiltration system had a significant impact on the observed TCE removal efficiency. TCE degradation rates were dependent on the inlet contaminant concentration as well as on the loading rate. No microbial inhibition was observed at inlet TCE concentrations as high as 87 parts per million on a volume basis.

Quantifying the effects of fumarate on in situ reductive dechlorination rates.

In situ methods are needed to evaluate the effectiveness of chemical amendments at enhancing reductive dechlorination rates in groundwater that is contaminated with the priority pollutant, trichloroethene (TCE). In this communication, a method that utilizes single-well, "push-pull" tests to quantify the effects of chemical amendments on in situ reductive dechlorination rates is presented and demonstrated. Five push-pull tests were conducted in each of five monitoring wells located in a TCE-contaminated aquifer at the site of a former chemical manufacturing facility. Rates for the reductive dechlorination of the fluorinated TCE-surrogate, trichlorofluoroethene (TCFE), were measured before (test 1) and after (test 5) three successive additions (tests 2-4) of fumarate. Fumarate was selected to stimulate the growth and activity of indigenous microorganisms with the metabolic capability to reduce TCFE and TCE. In three wells, first-order rate constants for the reductive dechlorination of TCFE increased by 8.2-92 times following fumarate additions. In two wells, reductive dechlorination of TCFE was observed after fumarate additions but not before. The transformation behavior of fumarate was also monitored following each fumarate addition. Correlations between the reductive dechlorination of TCFE and the reduction of fumarate to succinate were observed, indicating that these reactions were supported by similar biogeochemical conditions at this site.

In matrix derivatization of trichloroethylene metabolites in human plasma with methyl chloroformate and their determination by solid-phase microextraction-gas chromatography-electron capture detector.

Trichloroethylene (TCE) is a common industrial chemical that has been widely used as metal degreaser and for many industrial purposes. In humans, TCE is metabolized into dichloroacetic acid (DCA), trichloroacetic acid (TCA) and trichloroethanol (TCOH). A simple and rapid method has been developed for the quantitative determination of TCE metabolites. The procedure involves the in situ derivatization of TCE metabolites with methyl chloroformate (MCF) directly in diluted plasma samples followed by extraction and analysis with solid-phase microextraction (SPME) coupled to gas chromatography-electron capture detector (GC-ECD). Factors which can influence the efficiency of derivatization such as amount of MCF and pyridine (PYR), ratio of water/methanol were optimized. The factors which can affect the extraction efficiencies of SPME were screened using 2(7-4) Placket-Burman Design (PBD). A central composite design (CCD) was then applied to further optimize the most significant factors for optimum SPME extraction. The optimum factors for the SPME extraction were found to be 562.5mg of NaCl, pH at 1 and an extraction time of 22 min. Recoveries and detection limits of all three analytes in plasma were found to be in the range of 92.69-97.55% and 0.036-0.068 µg mL(-1) of plasma, respectively. The correlation coefficients were found to be in the range of 0.990-0.995. The intra- and inter-day precisions for TCE metabolites were found to be in the range of 2.37-4.81% and 5.13-7.61%, respectively. The major advantage of this method is that MCF derivatization allows conversion of TCE metabolites into their methyl esters in very short time (≤30 s) at room temperature directly in the plasma samples, thus makes it a solventless analysis. The method developed was successfully applied to the plasma samples of humans exposed to TCE.

Reductive dechlorination of the vinyl chloride surrogate chlorofluoroethene in TCE-contaminated groundwater.

At many trichloroethene (TCE)-contaminated field sites, microbial transformation of TCE results in the accumulation of vinyl chloride (VC), a known carcinogen and neurotoxin. Quantitative tools are needed to determine the in situ rates of VC transformation to ethene in contaminated groundwater. For this study, E-/Z-chlorofluoroethene (E-/Z-CFE) was evaluated as a surrogate for VC in laboratory microcosm and field push-pull tests. Single-well push-pull tests were conducted at a TCE-contaminated field site by injecting E-/Z-CFE and monitoring for the formation of fluoroethene (FE) over a period of up to 80 days. The rates for VC transformation to ethene and E-CFE transformation to FE were within a factor of 2.7 for laboratory microcosm systems and all preferentiallytransformed E-CFE over Z-CFE. In the field, the in situ rates of FE production from injected E-CFE ranged from 0.0018 to 1.15 microM/day, while the in situ rates of E-CFE disappearance ranged from 0.17 to 0.99 microM/day. No significant Z-CFE transformation was observed in field tests, which indicated preferential utilization of E-CFE over Z-CFE under in situ field conditions. The results of this study indicate E-CFE as a potential surrogate for estimating the in situ rates of VC transformation.

In situ anaerobic transformation of trichlorofluoroethene in trichloroethene-contaminated groundwater.

Methods are needed to obtain in situ information on the transformation rates of trichloroethene (TCE), the most commonly detected organic groundwater contaminant. The objective of this research was to investigate the potential for determining TCE transformation rates in groundwater by measuring the transformation rate of its fluorinated surrogate, trichlorofluoroethene (TCFE). To explore this hypothesis, the in situ transport behavior, transformation pathway, and transformation rate of injected TCFE were determined in TCE-contaminated groundwater using single-well, push-pull tests. Although transport behavior varied between wells, TCFE, dichlorofluoroethene (DCFE), and TCE were transported similarly to each other. In the shallow water-bearing zone, TCFE was reductively dechlorinated to cis-DCFE, trans-DCFE, and (E)-1-chloro-2-fluoroethene (CFE), while co-injected TCE was concurrently transformed to cis-dichloroethene (DCE), trans-DCE, 1,1-DCE, and a trace amount of chloroethene (CE). With added formate and the injected TCFE concentration being a factor of 20 higher than that of TCE, the TCFE transformation rate ranged from 0.053 to 0.30 mumol/L-day, while that of TCE ranged from 0.009 to 0.012 mumol/L-day. Without added formate, the TCFE transformation rate decreased to 0.036 mumol/L-day. In the deeper water-bearing zone, TCFE transformation occurred only after a lag time of 55 days with added formate. No TCFE transformation occurred in groundwater that had not previously been exposed to TCE. The potential applicability for TCFE as an in situ transport and transformation surrogate for TCE was demonstrated.

Oxidation of trichloroethylene by liver microsomal cytochrome P-450: evidence for chlorine migration in a transition state not involving trichloroethylene oxide.

Trichloroethylene (TCE) was metabolized by cytochrome P-450 containing mixed-function oxidase systems to chloral (2,2,2,-trichloroacetaldehyde), glyoxylic acid, formic acid, CO, and TCE oxide. TCE oxide was synthesized, and its breakdown products were analyzed. Under acidic aqueous conditions the primary products were glyoxylic acid and dichloracetic acid. The primary compounds formed under neutral or basic aqueous conditions were formic acid and CO. TCE oxide did not form chloral in any of these or other aqueous systems, even when iron salts, ferriprotoporphyrin IX, or purified cytochrome P-450 was present. Ferric iron salts catalyzed the rearrangement of TCE oxide to chloral only in CH2Cl2 or CH3CN. A 500-fold excess of iron was required for complete conversion. A kinetic model involving the zero-order oxidation of TCE to TCE oxide by cytochrome P-450 and the first-order degradation of the epoxide was used to test the hypothesis that TCE oxide is an obligate intermediate in the conversion of TCE to other metabolites. Kinetic constants fo the breakdown of TCE oxide and for the oxidative metabolism of TCE to stable metabolites were used to predict epoxide concentrations required to support the obligate intermediacy of TCE oxide. The maximum levels of TCE oxide detected in systems using microsomal fractions and purified cytochrome P-450 were 5-28-fold lower than those predicted from the model. The kinetic data and the discrepancies between the observed metabolites and TCE oxide breakdown products support the view that the epoxide is not an obligate intermediate in the formation of chloral, and an alternative model is presented in which chlorine migration occurs in an oxygenated TCE-cytochrome P-450 transition state.

"Forced mass balance" technique for estimating in situ transformation rates of sorbing solutes in groundwater.

A method for estimating in situ transformation rates of sorbing solutes in groundwater is presented. The method utilizes a novel data processing technique called "forced mass balance" (FMB) to remove the effects of transport processes from reactant and product concentrations measured during single-well, "push-pull" tests. The effectiveness of the FMB technique was evaluated by quantifying errors in derived rates obtained by applying FMB to simulated push-pull test data generated by a numerical model. Results from simulated tests indicated that errors in derived rates increase as the test duration, groundwater velocity, and ratio of reactant to product retardation factors increase. In addition, errors in derived rates increase as the reaction rate constant and aquifer dispersivity decrease. As a demonstration, the FMB technique was used to derive an in situ reductive dechlorination rate for trichlorofluoroethene (TCFE) using data from a field push-pull test. Error analyses indicated that the in situ TCFE transformation rate was underestimated by a factor of 1.1-2. Thus, the FMB technique makes it possible to estimate in situ transformation rates of sorbing solutes and when FMB is coupled with computer modeling to estimate errors in derived in situ rates.

The influence of trichloroethylene and related drugs on the vestibular system.

A previously described experimental model for studying the effect of industrial solvents on the vestibular system of rabbits has been applied to trichloroethylene. Estimation of trichloroethylene and its metabolites in blood and cerebrospinal fluid was performed by gas chromatography. Vestibular function was studied by recording nystagmus, induced by positional changes or accelerated rotation. At blood levels of trichloroethylene above 30 p.p.m. "positional nystagmus" develops. Two metabolites of trichloroethylene, chloral hydrate and trichloroethanol, which are known as central nervous system (CNS) depressants, did not induce this abnormal nystagmus. However, alpha-chloralose, a derivative of chloral hydrate, induced positional nystagmus and also a markedly exaggerated nystagmus developed during rotatory acceleration. It is suggested that solvents like trichloroethylene elicit vestibular disturbances by stimulation of central subcortical vestibulo-oculomotor connections. The stimulation may be caused by a blockage of inhibitory systems.