Search results for "cyclic"
showing 10 items of 2439 documents
Polycyclic aromatic hydrocarbons (PAHs) in coffee brew samples: analytical method by GC-MS, profile, levels and sources.
2009
Roasting is a crucial step for the production of coffee, as it enables the development of color, aroma, and flavor, which are essential for the characterization of the coffee quality. At the same time, roasting may lead to the formation of not desirable compounds, such as polycyclic aromatic hydrocarbons (PAHs). In this paper, we report a method for PAHs determination in coffee brew, based on saponification and liquid-liquid extraction with small volumes of hexane, with exclusion of further processes of purification since we analyze the extract by gas chromatography with mass spectrometric detectors in the single ion monitoring mode (SIM). The total concentration of the 28 compounds investi…
Reduction of ferricytochrome c catalyzed by optically active chromium(III) complexes
2009
The reduction rates of horse heart ferricytochrome c by amalgamated zinc or by electrolysis at fixed potential on a mercury pool as the cathode have been measured in a buffered solution at pH 7.5 by absorption spectrophotometry. In both cases, the reaction was strongly accelerated by the presence of the optically active complexes Lambda-[Cr(III)((S,S)-promp)H(2)O](+) (H(2)promp = N,N'-[(pyridine-2,6-diyl)bis(methylene)]-bis[(S)-proline]), Delta-[Cr(III)((R,R)-alamp)H(2)O](+) (H(2)alamp = N,N'-[(pyridine-2,6-diyl)bis(methylene)]-bis[(R)-alanine]) and Lambda-[Cr(III)((S,S)-alamp)(H(2)O)(2)](+). These were shown to undergo reversible one-electron reduction to the corresponding labile chromium(…
Metabolism of Phenanthrene, Benz[a]anthracene, Benzo[a]pyrene, Chrysene and Benzo[c]phenanthrene by Eight cDNA-expressed Human and Rat Cytochromes P4…
1996
Abstract Phenanthrene, benz[a]anthracene, chrysene, benzo[c]phenanthrene, and benzo[a]pyrene have been studied for their regiospecific oxidation by five human (1A1, 1A2, 2A6, 2E1, 3A4) and three rat (1A1, 1A2, 2B1) CYP isoforms. All substrates are preferentially metabolized by CYP1A1 and CYP1A2 in human and rat. Other isoforms play a minor role if at all. Significant differences between human and rat CYP isoforms can be recognized with regard to the regiospecific oxidation of PAH. For instance, K-region oxidation is more pronounced in rat than in human CYP1A1 and CYP1A2. Hence, extrapolation from metabolism studies in rodents to human may be limited.
Application of Dopant-Assisted Atmospheric Pressure Photoionisation HPLC–MS Method for the Sensitive Determination of Polycyclic Aromatic Hydrocarbon…
2017
Multiple food research studies have shown that the polycyclic aromatic hydrocarbon (PAHs) are frequently found in processed cocoa products and chocolate. In a present study a method based on dopant-assisted atmospheric pressure photoionisation (DA-APPI) combined with a liquid chromatography/high-resolution mass spectrometer (HPLC-HRMS) for high-sensitivity analysis of four EU marker PAHs in dark chocolate samples was developed and fully validated according to the performance criteria set in EU guidelines. PAHs detection was achieved by HRMS in positive electrospray ionization mode with toluene used as a dopant to enhance the ionization efficiency of non-polar PAHs. The on-column instrument …
Efficacy of Ozonation Treatments of Smoked Fish for Reducing Its Benzo[a]pyrene Concentration and Toxicity
2017
Ozone is widely used in food processing, for example, to decompose mycotoxins or pesticide residues, to extend the shelf life of products, and for sanitation. The objective of this study was to assess the possibility of expanding the application of ozone for oxidative degradation of polycyclic aromatic hydrocarbons (PAHs). The evaluation was conducted by ozonation of a benzo[a]pyrene (BaP) standard solution and smoked fish (sprats) contaminated with PAHs. The effect of ozonation was immediate in the BaP solution; 89% of this toxic compound was decomposed after only 1 min of treatment. However, the impact of ozonation on the smoked sprats was less pronounced, even after prolonged treatment. …
Extraction of polycyclic aromatic hydrocarbons from cookies: a comparative study of ultrasound and microwave-assisted procedures.
2008
The chromatographic determination of 15 polycyclic aromatic hydrocarbons (PAHs) in cookies has been improved in order to obtain a fast method with a low limit of detection through the combination of microwave-assisted extraction (MAE), oil saponification and solid-phase extraction clean-up before the injection of purified extracts in a C18 201TP52 (5 microm, 250 x 2.1 mm) column. Using acetonitrile-water as mobile phase, with a 50% to 95% w/w acetonitrile gradient for a fixed flow of 0.250 ml min(-1), 15 PAHs were separated in 45 min. The column temperature was maintained at 15 degrees C; and fluorimetric detection was made at a fixed excitation wavelength of 264 nm and emission measurement…
Genotoxicity characteristics of reverse diol-epoxides of chrysene.
2017
Trans-3,4-dihydroxy-3,4-dihydrochrysene (chrysene-3,4-diol), a major metabolite of chrysene, is further metabolized by rat liver enzymes to products which effectively revert the his- Salmonella typhimurium strain TA98 to histidine prototrophy, but are only weakly mutagenic in strain TA100 and in Chinese hamster V79 cells (acquisition of resistance to 6-thioguanine). The liver enzyme mediated mutagenicity of chrysene-3,4-diol is substantially enhanced in the presence of 1,1,1-trichloropropene 2,3-oxide, an inhibitor of microsomal epoxide hydrolase. The predominant metabolites of chrysene-3,4-diol, namely the anti- and syn-isomers of its 1,2-oxide (termed reverse diol-epoxides), proved to be …
Quinone reduction and redox cycling catalysed by purified rat liver dihydrodiol/3 alpha-hydroxysteroid dehydrogenase.
1992
A highly active preparation of rat liver dihydrodiol/3 alpha-hydroxysteroid dehydrogenase was obtained using a newly developed, rapid purification scheme involving affinity chromatography on Red Sepharose. Depending on the coenzyme present, the purified enzyme was found to catalyse the oxidation of dihydrodiols and steroids or the reduction of substrates with carbonyl or quinone moieties. Using a wide range of synthetic quinones derived from polycyclic aromatic hydrocarbons (PAHs), we observed a pronounced regioselectivity of the quinone reductase activity. Good substrates were the o-quinones of phenanthrene, benz(a)anthracene, chrysene and benzo(a)pyrene with the quinonoid moiety in the K-…
Covalent DNA adducts formed by benzo[c]chrysene in mouse epidermis and by benzo[c]chrysene fjord-region diol epoxides reacted with DNA and polynucleo…
1997
The metabolic activation in mouse skin of benzo[c]chrysene (B[c]C), a weakly carcinogenic polycyclic aromatic hydrocarbon (PAH) present in coal tar and crude oil, was investigated. Male Parkes mice were treated topically with 0.5 mumol of B[c]C, and DNA was isolated from the treated areas of skin at various times after treatment and analyzed by 32P-postlabeling. Seven adduct spots were detected, at a maximum level of 0.89 fmol of adducts/microgram of DNA. Four B[c]C-DNA adducts persisted in skin for at least 3 weeks. Treatment of mice with 0.5 mumol of the optically pure putative proximate carcinogens (+)- and (-)-trans-benzo[c]chrysene-9,10-dihydrodiols [(+)- and (-)-B[c]C-diols] led to th…
Synthesis and mutagenicity of the diastereomeric fjord-region 11,12-dihydrodiol 13,14-epoxides of dibenzo[a,l]pyrene.
1994
Extensive tumorigenicity studies in rodents revealed that dibenzo[a,l]pyrene (DB[a,l]P) is the most potent carcinogen among all polycyclic aromatic hydrocarbons (PAHs) tested so far. The structure of the genotoxic metabolite(s) responsible for this exceptional carcinogenicity is unknown. The fjord-region syn- and anti-DB[a,l]P-11,12-dihydrodiol 13,14-epoxides (syn- and anti-DB[a,l]PDE) were synthesized to clarify their role as possible ultimate mutagenic and carcinogenic metabolites of DB[a,l]P.9-Formyl-11,12-dimethoxybenzo[g] chrysene was prepared from 9-phenanthrylacetic acid by a photochemical route. After reaction of the aldehyde with trimethylsulfonium iodide to generate an oxiranyl si…