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Reference Substance (reference + substance)
Selected AbstractsModels for the estimation of a ,no effect concentration'ENVIRONMETRICS, Issue 1 2002Ana M. Pires Abstract The use of a no effect concentration (NEC), instead of the commonly used no observed effect concentration (NOEC), has been advocated recently. In this article models and methods for the estimation of an NEC are proposed and it is shown that the NEC overcomes many of the objections to the NOEC. The NEC is included as a threshold parameter in a non-linear model. Numerical methods are then used for point estimation and several techniques are proposed for interval estimation (based on bootstrap, profile likelihood and asymptotic normality). The adequacy of these methods is empirically confirmed by the results of a simulation study. The profile likelihood based interval has emerged as the best method. Finally the methodology is illustrated with data obtained from a 21 day Daphnia magna reproduction test with a reference substance, 3,4-dichloroaniline (3,4-DCA), and with a real effluent. Copyright © 2002 John Wiley & Sons, Ltd. [source] The search for the "ideal" soil toxicity test reference substanceINTEGRATED ENVIRONMENTAL ASSESSMENT AND MANAGEMENT, Issue 3 2007Jörg Römbke [source] Hydroxyl radical reactions with halogenated ethanols in aqueous solution: Kinetics and thermochemistryINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2008I. Morozov Laser flash photolysis combined with competition kinetics with SCN, as the reference substance has been used to determine the rate constants of OH radicals with three fluorinated and three chlorinated ethanols in water as a function of temperature. The following Arrhenius expressions have been obtained for the reactions of OH radicals with (1) 2-fluoroethanol, k1(T) = (5.7 ± 0.8) × 1011 exp((,2047 ± 1202)/T) M,1 s,1, (2) 2,2-difluoroethanol, k2(T) = (4.5 ± 0.5) × 109 exp((,855 ± 796)/T) M,1 s,1, (3) 2,2,2-trifluoroethanol, k3(T) = (2.0 ± 0.1) × 1011 exp((,2400 ± 790)/T) M,1 s,1, (4) 2-chloroethanol, k4(T) = (3.0 ± 0.2) × 1010 exp((,1067 ± 440)/T) M,1 s,1, (5) 2, 2-dichloroethanol, k5(T) = (2.1 ± 0.2) × 1010 exp((,1179 ± 517)/T) M,1 s,1, and (6) 2,2,2-trichloroethanol, k6(T) = (1.6 ± 0.1) × 1010 exp((,1237 ± 550)/T) M,1 s,1. All experiments were carried out at temperatures between 288 and 328 K and at pH = 5.5,6.5. This set of compounds has been chosen for a detailed study because of their possible environmental impact as alternatives to chlorofluorocarbon and hydrogen-containing chlorofluorocarbon compounds in the case of the fluorinated alcohols and due to the demonstrated toxicity when chlorinated alcohols are considered. The observed rate constants and derived activation energies of the reactions are correlated with the corresponding bond dissociation energy (BDE) and ionization potential (IP), where the BDEs and IPs of the chlorinated ethanols have been calculated using quantum mechanical calculations. The errors stated in this study are statistical errors for a confidence interval of 95%. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 174,188, 2008 [source] In vitro protective effect of Rhodiola rosea extract against hypochlorous acid-induced oxidative damage in human erythrocytesBIOFACTORS, Issue 3 2004Roberta De Sanctis Abstract Rhodiola rosea L. (Crassulaceae) is a plant living at high altitudes in Europe and Asia. Its roots have long been used in the traditional medical system of these geographical areas to increase the organism resistance to physical stress; today, it has become an important component of many dietary supplements. In this study we investigate the antioxidant capacity of the R. rosea aqueous extract evaluating its ability to counteract some of the main damages induced by hypochlorous acid (HOCl), a powerful oxidant generated by activated phagocytes, to human erythrocytes. Ascorbic acid was used as a reference substance because of its physiological HOCl-scavenging ability. Our study demonstrates that R. rosea is able to significantly protect, in a dose-dependent manner, human RBC from glutathione (GSH) depletion, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) inactivation and hemolysis induced by the oxidant. Furthermore, we demonstrate that R. rosea aqueous extract acts from the inside of the erythrocyte suggesting a probable involving of cell components. The protection on GSH afforded by the R. rosea extract with respect to ascorbic acid, occurred also if added 2 or 5 min. later than the oxidant, suggesting a more rapid or powerful effect. [source] Structure, DNA Binding Studies and Cytotoxicity of Complex [Pd(phen)(L -asp)]·3H2OCHINESE JOURNAL OF CHEMISTRY, Issue 6 2009Enjun GAO Abstract The palladium(II) complex of [Pd(phen)(L -asp)]·3H2O (phen=1,10-phenanthroline, H2L-asp=L -aspartic acid) has been synthesized from a solution reaction and analyzed by elemental analyses, 1H NMR and IR spectra. Moreover, the complex has been structurally characterized by single-crystal X-ray diffractometry. The cytotoxicity assay of the complex and cis -DDP as reference substance against three different cancer cell lines (Hela, Hep-G2 and KB) has been conducted. The results show that the Pd complex exhibits higher cytotoxicity against Hela system. The study on the interaction of the Pd complex with fish sperm DNA (FS-DNA) has been performed with diverse spectroscopic techniques, showing that the complex is bound to the fish sperm DNA via an intercalative mode. Gel electrophoresis assay demonstrates the ability of the complex to cleave the pBR 322 plasmid DNA. [source] Identification of organic eluates from four polymer-based dental filling materialsEUROPEAN JOURNAL OF ORAL SCIENCES, Issue 3 2003Vibeke Barman Michelsen Elution from polymer-based dental filling materials may have a potential impact on the biocompatibility of the materials. Since information from the manufacturers about ingredients in the materials often is incomplete, analyses of eluates from the materials are necessary for a better knowledge about possible harmful compounds. The aim of this study was to identify organic eluates from polymerized samples of two composites, one compomer and one resin-reinforced glass ionomer cement. Samples were immersed in ethanol or Ringer's solution. Organic leachables were analyzed by gas chromatography,mass spectrometry. Identification was confirmed with reference substances, if available. Among components detected were monomers, co-monomers, initiators, stabilizers, decomposition products and contaminants. Thirty-two substances were identified and 17 were confirmed with reference substances. From elution in Ringer's we identified 13 eluates from Tetric Ceram, 10 from Z250, 21 from Dyract and six from Fuji II LC; HEMA, HC and CQ were found in all samples. From elution in ethanol 12 eluates from Tetric Ceram, 18 eluates from Z250, 19 from Dyract and 10 from Fuji II LC were identified. The diversity of eluates from the four materials under study is demonstrated. Owing to variation between the materials, the biocompatibility including the allergenic potential may be different. [source] Prediction of human pharmacokinetics,gut-wall metabolismJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 10 2007Urban Fagerholm Intestinal mucosal cells operate with different metabolic and transport activity, and not all of them are involved in drug absorption and metabolism. The fraction of these cells involved is dependent on the absorption characteristics of compounds and is difficult to predict (it is probably small). The cells also appear comparably impermeable. This shows a limited applicability of microsome intrinsic clearance (CLint)-data for prediction of gut-wall metabolism, and the difficulty to predict the gut-wall CL (CLGW) and extraction ratio (EGW). The objectives of this review were to evaluate determinants and methods for prediction of first-pass and systemic EGW and CLGW in man, and if required and possible, develop new simple prediction methodology. Animal gut-wall metabolism data do not appear reliable for scaling to man. In general, the systemic CLGW is low compared with the hepatic CL. For a moderately extracted CYP3A4-substrate with high permeability, midazolam, the gut-wall/hepatic CL-ratio is only 1/35. This suggests (as a general rule) that systemic CLGW can be neglected when predicting the total CL. First-pass EGW could be of importance, especially for substrates of CYP3A4 and conjugating enzymes. For several reasons, including those presented above and that blood flow based models are not applicable in the absorptive direction, it seems poorly predicted with available methodology. Prediction errors are large (several-fold on average; maximum-15-fold). A new simple first-pass EGW -prediction method that compensates for regional and local differences in absorption and metabolic activity has been developed. It has been based on human cell in-vitro CLint and fractional absorption from the small intestine for reference (including verapamil) and test substances, and in-vivo first-pass EGW -data for reference substances. First-pass EGW -values for CYP3A4-substrates with various degrees of gastrointestinal uptake and CLint and a CYP2D6-substrate were well-predicted (negligible errors). More high quality in-vitro CLint - and in-vivo EGW -data are required for further validation of the method. [source] | |||||||||||||