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[en] A series of thirteen regiospecifically chlorine-37 labeled polychlorodibenzo-p-dioxins were synthesized via the Sandmeyer reaction. Nitrochlorodibenzodioxins which were obtained by a base promoted condensation of catechols and dinitropolyhalobenzenes were reduced and converted to the diazonium salts. Chlorine-37 was introduced using cuprous chloride-37. The isotopic enrichment was in the range 75-96%. (Author)
[en] Thermodynamic functions (ΔGf and ΔHf) of clorinated dibenzo-p-dioxins (ClnDD) with n = 0–8 were calculated at the DFT level of theory using the B3LYP functional and extended 6–31** basis sets and used to analyze possible relationship of the structures and energy characteristics of these compounds with their toxicity. A new sequence of successive isodesmic reactions, which makes it possible to calculate chemical potentials μG and μH from the ΔGf and ΔHf values, has been proposed. In the framework of this approach, satisfactory linear correlations between the chemical potentials μ and the logarithms of toxicity of the corresponding polychlorodioxins were obtained for the first time.
[en] Quantifying polychlorinated biphenyl (PCB) residues in nestlings of avian species is a common method for assessing trophic transfer and risk at PCB-contaminated sites. The proportion of nestling PCB mass due to maternal transfer is often accounted for by subtracting total PCB mass in eggs from nestlings. However, variation in physicochemical properties and metabolism among congeners may lead to differences between egg contribution based on total PCBs and dioxin-like congeners. We examined congener-specific variation in contribution of PCBs from eggs to nestlings in tree swallows and European starlings. Egg contribution of total PCB mass was 14.3 and 16.2%, respectively, whereas contribution based on dioxin-like congeners was 14.8 and 13.6%, respectively. These data suggest that using total PCB mass in eggs to adjust estimates of PCB accumulation in nestlings may not reflect patterns for dioxin-like congeners, potentially over or under-estimating the risk of toxicity of PCBs. - Congener-specific contribution of PCBs from egg to nestlings was examined.
[en] Organohalogen pollutants are of concern in many river and estuarine environments, such as the New York-New Jersey Harbor estuary and its tributaries. The Hackensack River is contaminated with various metals, hydrocarbons and halogenated organics, including polychlorinated biphenyls (PCBs) and polychlorinated dibenzo-p-dioxins. In order to examine the potential for microbial reductive dechlorination by indigenous microorganisms, sediment samples were collected from five different estuarine locations along the Hackensack River. Hexachlorobenzene (HCB), hexabromobenzene (HBB), and pentachloroaniline (PCA) were selected as model organohalogen pollutants to assess anaerobic dehalogenating potential. Dechlorinating activity of HCB and PCA was observed in sediment microcosms for all sampling sites. HCB was dechlorinated via pentachlorobenzene (PeCB) and trichlorobenzene (TriCB) to dichlorobenzene (DCB). PCA was dechlorinated via tetrachloroaniline (TeCA), trichloroanilines (TriCA), and dichloroanilines (DCA) to monochloroaniline (MCA). No HBB debromination was observed over 12 months of incubation. However, with HCB as a co-substrate slow HBB debromination was observed with production of tetrabromobenzene (TeBB) and tribromobenzene (TriBB). Chloroflexi specific 16S rRNA gene PCR-DGGE followed by sequence analysis detected Dehalococcoides species in sediments of the freshwater location, but not in the estuarine site. Analysis targeting 12 putative reductive dehalogenase (rdh) genes showed that these were enriched concomitant with HCB or PCA dechlorination in freshwater sediment microcosms. - Highlights: • Indigenous bacteria from Hackensack River sediments were capable of dehalogenating hexachlorobenzene and pentachloroaniline. • Dehalococcoides species were enriched in freshwater sediment spiked with hexachlorobenzene and pentachloroaniline. • Putative reductive dehalogenase genes were enriched in hexachlorobenzene and pentachloroaniline dechlorinating microcosms. - Halogenated aromatic pollutants are reductively dehalogenated by indigenous microorganisms in an estuarine river system.
[en] Generation of mitochondrial reactive oxygen species (ROS) can be perturbed following exposure to environmental chemicals such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Reports indicate that the aryl hydrocarbon receptor (AhR) mediates TCDD-induced sustained hepatic oxidative stress by decreasing hepatic ATP levels and through hyperpolarization of the inner mitochondrial membrane. To further elucidate the effects of TCDD on the mitochondria, high-throughput quantitative real-time PCR (HTP-QRTPCR) was used to evaluate the expression of 90 nuclear genes encoding mitochondrial proteins involved in electron transport, oxidative phosphorylation, uncoupling, and associated chaperones. HTP-QRTPCR analysis of time course (30 μg/kg TCDD at 2, 4, 8, 12, 18, 24, 72, and 168 h) liver samples obtained from orally gavaged immature, ovariectomized C57BL/6 mice identified 54 differentially expressed genes (|fold change| > 1.5 and P-value < 0.1). Of these, 8 exhibited a sigmoidal or exponential dose-response profile (0.03 to 300 μg/kg TCDD) at 4, 24 or 72 h. Dose-responsive genes encoded proteins associated with electron transport chain (ETC) complexes I (NADH dehydrogenase), III (cytochrome c reductase), IV (cytochrome c oxidase), and V (ATP synthase) and could be generally categorized as having proton gradient, ATP synthesis, and chaperone activities. In contrast, transcript levels of ETC complex II, succinate dehydrogenase, remained unchanged. Putative dioxin response elements were computationally found in the promoter regions of all 8 dose-responsive genes. This high-throughput approach suggests that TCDD alters the expression of genes associated with mitochondrial function which may contribute to TCDD-elicited mitochondrial toxicity.
[en] Supercritical fluid extraction (SFE), ultrasonic extraction (USE), and accelerated solvent extraction (ASE) were compared with the well known Soxhlet extraction for the extraction of polychlorinated biphenyls (PCBs) and polychlorinated dibenzo-p-dioxins (PCDDs) from the XAD-2 resin which was used to adsorb PCDDs in the atmosphere. XAD-2 resin spiked with five PCDDs was chosen as a sample. The optimum conditions for the extraction of PCDDs by SFE were turned out to be the use of CO2 modified with 10% toluene at 100 .deg. C and 350 atm, with 5 min static extraction followed by 20 min dynamic extraction. SFE gave a good extraction rate with good reproducibility for PCDDs ranging from 68 to 98%. The ultrasonic extraction of PCDDs from XAD-2 was investigated and compared with other extractions. A probe type method was compared with a bath type. Two extraction solvents, toluene and acetone were compared with their mixture. The use of their mixture in probe type, with 9 minutes of extraction time, was found to be the optimum condition. The average recovery of the five PCDDs for USE was 82-93%. Accelerated solvent extraction (ASE) with a liquid solvent, a new technique for sample preparation, was performed under elevated temperatures and pressures. The effect of temperature on the efficiency of ASE was investigated. The extraction time for a 10 g sample was less than 15 min, when the organic solvent was η-hexaneacetone mixture (1 : 1, v/v). Using ASE, the average recoveries of five PCDDs ranged from 90 to 103%. SFE, USE, and ASE were faster and less laborious than Soxhlet extraction. The former three methods required less solvent than Soxhlet extraction. SFE required no concentration of the solvent extracts. SFE and ASE failed to perform simultaneous parallel extractions because of instrumental limitations
[en] A new methodology for construction of dihydro-1,4-dioxin skeleton was described. Introduction of thio group at the α-position of 8 followed by chlorination gave 11, which was to prevent an enolization as well as to promote the facile nucleophilic substitution reaction of ethylene glycol giving 16 in equilibrium with cyclic ether 19. Removal of thio group of 19 and dehydration in the presence of an acid catalyst gave dihydro-1,4-dioxin 21. In case of electron withdrawing trifluoromethyl group is substituted in C-2, 18 was converted to the corresponding dihydro-1,4-dioxin 20 by the halogenation of hydroxy followed by treatment of thiethylamine
[en] Polyhydroxylated dibenzo-p-dioxins (PHODDs) are important metabolic and synthetic products of polychlorinated dibenzo-p-dioxins (PCDDs). Two types of hydrogen bonds exist in PHODD molecules: one between a hydroxyl group (HO) and an oxygen atom of the ether bond, and the other between two ortho hydroxyls of a benzene ring. By fully optimized calculation with density functional theory (DFT), their bond energies were ascertained to be approximately 9–14 kJ/mol and 15–19 kJ/mol respectively by the comparison of standard Gibbs energy of formation (ΔfGθ) between different molecules, which was experimentally verified. The two types of hydrogen bonds affect the hydrophilicity and stability of the molecules. The torsional potential of hydroxyls and the orientation making the congener most stable were obtained. The octanol-water partition coefficients (logKows) were calculated based on the group contribution method, and the standard state entropy (Sθ), standard enthalpy (ΔfHθ) of formation and ΔfGθ were obtained from the combination of DFT calculation and isodesmic reaction for the stable PHODD congeners. The number and position of hydroxyl substitution (NPHOS) were employed as descriptors to establish quantitative structure–property relationship (QSPR) models. Although the hydrophilicity of PHODDs increases with the number of hydroxyl groups, it is impaired by the intramolecular hydrogen bonds. The logKows of PHODDs are much smaller than those of PCDDs, and the variation trend with the number of substituents is different. In addition, the relative stability order of PHODD congeners was theoretically proposed, which is quite different from that of PCDDs. Considering the ionization in water, first-order ionization constants of PHODDs were calculated according to the results of SMD method of Self-Consistent Reaction Field Theory (SCRF), and they were influenced by the hydrogen bonds. - Highlights: ► Hydroxyl torsional potential and hydrogen bond energies in PHODDs are obtained. ► Thermodynamic properties, logKow and pKas are obtained. ► Thermodynamic properties, logKow have good relations with substitution pattern. ► Relative stability order and logKow of PHODDs differ from those of PCDDs. ► How hydrogen bond affects the studied properties is revealed.
[en] Research highlights: → Evodiamine interacted with the AhR. → Evodiamine inhibited the specific binding of [3H]-TCDD to the AhR. → Evodiamine acts as an antagonist of the AhR. -- Abstract: Evodiamine, the major bioactive alkaloid isolated from Wu-Chu-Yu, has been shown to interact with a wide variety of proteins and modify their expression and activities. In this study, we investigated the interaction between evodiamine and the aryl hydrocarbon receptor (AhR). Molecular modeling results revealed that evodiamine directly interacted with the AhR. Cytosolic receptor binding assay also provided the evidence that evodiamine could interact with the AhR with the Ki value of 28.4 ± 4.9 nM. In addition, we observed that evodiamine suppressed the 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induced nuclear translocation of the AhR and the expression of CYP1A1 dose-dependently. These results suggested that evodiamine was able to bind to the AhR as ligand and exhibit antagonistic effects.
[en] Biochars have increasingly been used as adsorbents for organic and inorganic contaminants in soils. However, during the carbonization process of pyrolysis, contaminants, including polycyclic aromatic hydrocarbons (PAHs) and polychlorinated dioxins and furans (PCDD/DF) can be generated. In this study, biochars made from sawdust, were prepared at various temperatures ranging from 250 to 700 °C. The Microtox® and rat hepatoma cell line H4IIE-luc assays were used to characterize the general toxic and effects, mediated through the aryl hydrocarbon receptor (AhR), or dioxin-like potencies of organic extracts of biochars. The greatest total concentrations of PAHs (8.6 × 102 μg kg−1) and PCDD/DF (6.1 × 102 pg g−1) were found in biochar generated at 400 °C and 300 °C, respectively. Results of the H4IIE-luc assay, which gives total concentrations of 2,3,7,8-TCDD equivalents (TEQH4IIE-luc), indicated that total potencies of aryl hydrocarbon receptor (AhR) agonists were in decreasing order: 300 °C > 250 °C > 400 °C > 500 °C > 700 °C. The 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQchem) calculated as the sum of products of 16 PAHs and 17 PCDD/DF congers multiplied by their respective relative potencies (RePs) was less than that of TEQH4IIE-luc determined by use of the bioanalytical method, with the H4IIE-luc assay, which measures the total dioxin-like potency of a mixtures. The ratio of TEQchem/TEQH4IIE-luc was in the range of 0.7%–3.8%. Thus, a rather small proportion of the AhR-mediated potencies extracted from biochars were identified by instrumental analyses. Results of the Microtox test showed similar tendencies as those of the H4IIE-luc test, and a linear correlation between EC50 of Microtox test and EC20 of H4IIE-luc test was found. The results demonstrated that biochars produced at higher pyrolysis temperatures (>400 °C) were less toxic and had lower potencies of AhR-mediated effects, which may be more suitable for soil application. - Highlights: • Biochars from sawdust were prepared at various temperatures. • The greatest PAHs and PCDD/DF were found at 400 °C and 300 °C, respectively. • H4IIE-luc assay indicated highest AhR activity at 300 °C. • Values of TEQchem calculated were much less than that of TEQH4IIE. - Potencies of aryl hydrocarbon receptor (AhR) agonists varied among biochars produced at various pyrolysis temperatures.