Until now, no data are available concerning the biotransformation and toxicity of 2-methylpropene (or isobutene), a gaseous alkene widely used in industry (rubber, fuel additives, plastic polymers, adhesives, antioxidants). In this work, the biotransformation of 2-methylpropene (MP) has been studied, using total liver homogenates of mice, supplemented with a NADPH-generating system. In analogy to other olefins, 2-methylpropene is metabolized to its epoxide 2-methyl-1,2-epoxypropane (MEP), as proved by the identification by gas chromatography coupled with mass spectrometry. The epoxidation is cytochrome P-450 dependent, as shown by experiments in the absence of the NADPH-generating system and in the presence of various concentrations of metyrapone and SKF 525-A, two known inhibitors of the mono-oxygenases. A simple gas chromatographic headspace method has been developed for the quantitative determination of the epoxide formed. The formation of MEP is never linear in function of time and it reaches a maximum after 20 min. Thereafter is decreases continuously to undetectable levels. This observation can be explained by the immediate action of epoxide hydrolase and glutathione S-transferase, converting the epoxide to 2-methyl-1,2-propanediol and to the glutathione conjugate respectively. The involvement of both enzymes has been demonstrated by the addition of 3,3,3-trichloropropene oxide and indomethacin. These inhibitors of, respectively, epoxide hydrolase and glutathione S-transferase increase the epoxide formation in a significant way. The actual concentration of MEP is therefore not only dependent on its formation by cytochrome P-450 dependent mono-oxygenases, but also on its conversion by epoxide hydrolase and glutathione S-transferase, both very active in liver tissue.
ZUSAMMENFASSUNG:Es werden mehrere SynthesemiSglichkeiten fur die Herstellung von an Cellulose immobilisierten 8-Hydroxychinolin-und 8-Hydroxychinolin-5-sulfonsaure-Derivaten beschrieben, die zu einem Produkt mit einer Kapazitat von 500-800 pmol/g, hoher Austauschgeschwindigkeit und guter Stabilitat gegenuber dem Eluenten fiihren. Die scheinbare Komplexbildungskonstante der Oxincellulosen mit Zn2+ ist etwa 2 * 1 O5 mol-' dm3. SUMMARY:Some routes to synthetize covalently bound chelating groups as 8-hydroxyquinoline or 8-hydroxyquinoline-5-sulfonic acid to cellulose are given. The products show a capacity of 500 -800 pmol/g, fast kinetics of exchange and good stability against the eluent. The apparent stability constant of the complexes with ZnZ+ are around 2 lo5 mol-' dm3.
Automated preconcentration techniques for off/on-line determination with ICP-OES have been developed for various metal ions of environmental interest. Preconcentration studies were performed on two different types of chemically bonded chelating ion-exchangers, namely EDTrA-cellulose (iminoacetate groups) and HSO 3 9 oxine-cellulose. Enrichment studies were carried out at various preconcentration factors and also at different loadings.Inductively coupled plasma emission spectroscopy has been widely used in determination of trace elements in environmental samples. Although the method is very sensitive, it sometimes poses problems on direct determination at detection limits and also in presence of large amounts of interfering matrix constituents. Preconcentration techniques combined with ICP-OES either off-[1, 2] or on-line [-3, 4], are found to be useful in solving these complex analytical problems. These methods provide high enrichment factors and lower detection limits by selective extraction of metals of interest from the complex matrix. As the sample throughput with ICP-OES is fairly high for multi-element analysis, it therefore demands faster sample preparation procedures. Hence the need of an automated preconcentration apparatus is justified. It not only helps in reducing the time, but also the closed system for sample handling makes it contamination-free. Additionally, on coupling it directly to a simultaneous ICP-AE [3,4] or flame AA [-5, 6] spectrometer and integrating the transient elution peak, detection limits can be lowered by an order of magnitude. Also these on-line methods require lesser volumes for enrichment as compared to manual off-line ones.
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