Polychlorinated Diphenyl Ethers Research Articles

Substituent effects on 13C NMR parameters of chlorinated diphenyl ethers. A multiple linear regression analysis

Abstract13C NMR chemical shifts and nJ(C,H) coupling constants of polychlorinated diphenyl ethers (PCDEs) were measured and analysed. The chlorine substituent effects on the chemical shifts and the coupling constants were determined by a multiple linear regression analysis. The 13C NMR chemical shifts depend on the conformational preferences in PCDEs. In addition to single substituent effects, corrective terms reflecting the conformational state of the molecule and the mutual steric interactions of two chlorine atoms had to be taken into account for the reliable prediction of the 13C chemical shifts. In contrast to chemical shifts, conformational effects play a minor role in the substituent effects of the nJ(C,H) coupling constants. Coupling constants are approximately additive in terms of ‘simple sum rules’.

Isomer-specific determination of 79 polychlorinated diphenyl ethers (PCDE) in cod liver oils, chlorophenols and in a fly ash

The occurrence of polychlorinated diphenyl ethers (PCDEs) has been investigated in two different cod liver oils produced in 1985 and 1993, respectively, from North-Atlantic fish. These samples mirror the distribution of PCDEs among other persistent organochlorine compounds in the marine environment. To elucidate the input of PCDEs in the environment, five possible sources of PCDEs have been analyzed, namely two wood preserving formulations containing approximately 10% pentachlorophenol, two technical chlorophenol products, and one fly ash from a municipal waste incinerator. The determination has been based on 106 available PCDE congeners. During sample preparation a 2-(l-pyrenyl)ethyldimethylsilylated silica column has been used in the normal phase mode to separate the PCDEs from possible PCDF interferences. The PCDEs have been quantified by high resolution gas chromatography/mass spectrometry on a SE 54 capillary column using electron ionization and selected ion monitoring. The total amount of PCDEs in 2,3,4,6-tetrachlorophenol have been determined to be 213 mg/kg. The lowest concentrations of PCDEs have been found in the more recently produced cod liver oil (sum PCDEs: 49 μg/kg) and in the fly ash sample (sum PCDEs: 93 µg/kg), respectively. The isomer-specific analysis has been employed to characterize the relationship between possible sources and the PCDEs found in the environment. PCDEs, like PCBs, can be indicator molecules for the global pollution of the environment.

New qsar models for polyhalogenated aromatics

AbstractElectronic properties of polychlorinated dibenzo p dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs), and polychlorinated diphenyl ethers (PCDEs) were calculated using the semi‐empirical AM1 method The calculated electronic descriptors — the energy of the lowest unoccupied molecular orbital (ELUMO), the energy of the highest occupied molecular orbital (EHOMO), the ELUMO‐EHOMO gap (dE), and molecular polarizability — are related to the Ah receptor binding affinity values of PCDDs, PCDFs, and PCBs and immunotoxicity values for PCDEs The quantitative structure activity relationships (QSARs) based on chlorine substitution patterns were also constructed, and they proved to be very predictive for Ah receptor binding Significant correlations of the electronic factors were found between the dE and Ah receptor binding affinities for PCDDs, PCDFs, and PCBs and for immunotoxicity of PCDEs A combination of descriptors ELUMO and the total number of chlorine atoms attached to a molecule (nCl) gives significant correlation for the Ah receptor binding of PCDFs and for immunotoxicity of PCDEs Hydrophobicity values taken from the literature were shown to be non‐significant for toxicity prediction of these polychlorinated compounds

Substituent effects of 1H NMR parameters of chlorinated diphenyl ethers. A statistical approach

AbstractThe 1H NMR spectra of 64 polychlorinated diphenyl ethers (PCDEs) were measured and assigned. Multiple linear regression analysis was used to estimate the effects of chlorine atoms on the 1H NMR chemical shifts and coupling constants. The ‘simple sum rules’ were found to be inadequate for the prediction of 1H NMR chemical shifts of PCDEs. Therefore, corrective terms of two chlorine atoms were taken into account. The most important effects on chemical shifts were shown to be the steric interactions of two adjacent chlorine atoms and the intramolecular ring current effect observed in the ortho‐proton of tri‐ortho‐substituted PCDEs. The substituent effects on J(HH) coupling constants were found to be approximately additive. An interannular coupling between ortho‐protons [6J(HH) = 0.05–0.15 Hz] of adjacent rings was observed.

Synthesis, Structure Verification, and Chromatographic Relative Retention Times for Polychlorinated Diphenyl Ethers

Fifty-four polychlorinated diphenyl ether (PCDEs) congeners were synthesized, and their structures were confirmed by mass spectrometry and proton magnetic resonance spectroscopy. The gas chromatographic relative retention times (RRT) for the PCDEs were determined relative to a reference standard, [ 13 C-3,3',4,4']-tetrachlorobiphenyl (PCB 77) on the fused silica capillary columns of SE-54 and OV-1701. The retention times for PCDEs increased with the increasing number of vicinal chlorines within a series of isomers. The chlorine substitution patterns of PCDEs were used to develop a method for predicting RRTs for congeners that were not synthesized

Metal reclamation produces sulphur analogues of toxic dioxins and furans

Polychlorinated dibenzothiophenes (PCDBTs), polychlorinated thianthrenes (PCTAs) and polychlorinated diphenylsulphides (PCDPSs) which are sulphur analogues for polychlorinated dibenzofurans (PCDFs), polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated diphenyl ethers (PCDEs), were analyzed by HRGC/HRMS in different samples from a metal reclamation plant. The samples were gas phase samples from an aluminium smelter and a car shredder and ash and slag from processes where different temperatures (300–850 °C) were used. Tri-, tetra-and pentaCDBTs were most abundant sulphur chloroaromatics at amounts comparable to PCDDs and PCDFs in emissions and wastes. Small amounts of tri- and tetraCTAs were identified in car shredder samples. Occurence of PCDPSs remained uncertain due to interferences even in GC/HRMS analyses.

Relationship between structure and retention of polychlorinated diphenyl ethers (PCDE) in HRGC in comparison with other groups of halogenated aromatic compounds

The GC-retention of 106 polychlorinated diphenyl ethers (PCDE) has been examined on five different stationary phases representing a broad range of polarities: CP Sil8/10%C18 (Sil8-type with 10% of octadecyl groups), SE 54 (methyl-/5% phenyl-polysiloxane), OV 1701 (7% phenyl-/7% cyanopropyl-polysiloxane), DB Dioxin (a polysiloxane phase, which incorporates 44% methyl, 28% phenyl, 20% cyanopropyl and 8% polyethylene groups) and SP 2331 (90% biscyanopropyl-/10% phenylcyanopropyl (1:1)-polysiloxane). Standard narrow-bore columns (0.2–0.3 mm i.d.) were used. Structural principles for the retention of the PCDEs in gas chromatography were compared with the retention behaviour of the closely related polychlorinated biphenyls (PCB) and the tetrachloro-methyl-diphenylmethanes (tetrachlorobenzyltoluenes, TCBT). The structure-retention behaviour of the PCDEs is partly similar to the TCBTs in spite of the differences in polarity. The differences between the structure-retention behaviour of the PCDEs and the PCBs can best be explained with the increasing possibility of a coplanar arrangement of PCBs with a decreasing number of chlorine substituents in the ortho positions of the phenyl-phenyl bond.

NEW QSAR MODELS FOR POLYHALOGENATED AROMATICS

Electronic properties of polychlorinated dibenzo p dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs), and polychlorinated diphenyl ethers (PCDEs) were calculated using the semi-empirical AM1 method The calculated electronic descriptors — the energy of the lowest unoccupied molecular orbital (ELUMO), the energy of the highest occupied molecular orbital (EHOMO), the ELUMO-EHOMO gap (dE), and molecular polarizability — are related to the Ah receptor binding affinity values of PCDDs, PCDFs, and PCBs and immunotoxicity values for PCDEs The quantitative structure activity relationships (QSARs) based on chlorine substitution patterns were also constructed, and they proved to be very predictive for Ah receptor binding Significant correlations of the electronic factors were found between the dE and Ah receptor binding affinities for PCDDs, PCDFs, and PCBs and for immunotoxicity of PCDEs A combination of descriptors ELUMO and the total number of chlorine atoms attached to a molecule (nCl) gives significant correlation for the Ah receptor binding of PCDFs and for immunotoxicity of PCDEs Hydrophobicity values taken from the literature were shown to be non-significant for toxicity prediction of these polychlorinated compounds

AM1 and single-crystal X-ray diffraction study of the conformational properties of chlorinated diphenyl ethers

Structural and conformational properties of 11 polychlorinated diphenyl ethers (PCDEs)1–11 and thyroxine derivative 12 were studied by the semiempirical AM1 method. In addition, the molecular structures of six PCDEs 1-6 were solved by X-ray crystallography. Conformational analyses for diphenyl ethers 1–12 were performed and the resulting conformational energy maps obtained. The calculated energy minima of PCDEs were obtained, and the structural parameters were compared with the X-ray structures. The X-ray-determined geometries were found to be inside the low-energy regions close to the global energy minima except for compound 2, whose X-ray structure deviates considerably from the global minima. The X-ray structures of PCDE were non-planar, with dihedral angles between two benzene rings ranging from 59.0° to 99.7°.

Contents and origin of polychlorinated diphenyl ethers (PCDE) in salmon from the Baltic Sea, Lake Saimaa and the Tenojoki river in Finland

The presence of 26 congeners of polychlorinated diphenyl ethers (PCDEs) was investigated in salmon from three locations in Finland. In addition to salmon, one chlorophenol wood preservative (Ky-5) and one fly ash sample were analyzed for PCDEs. Concentrations of PCDE congeners in salmon muscle measured by high resolution gas chromatography/low resolution mass spectrometry ranged from < 0.02 to 2.4 ng/g fresh weight. The major components of tetra- to octachlorinated PCDEs in salmon were one TeCDE (22′44′-), two PeCDEs (22′44′5- and 23′44′5-) and three HxCDEs (22′44′56′-, 22′44′55′- and 22′344′5-). The Baltic salmon caught from the Simojoki River had higher levels of PCDEs than the Atlantic salmon from the Tenojoki River or salmon from Lake Saimaa in South-Finland. Same PCDE congeners which were abundant in the wood preservative were also detected in salmon, whereas PCDE congeners in the fly ash were different from those in salmon or in Ky-5.

Bioaccumulation of dioxins, coplanar PCBs, PCDEs, HxCNs, R-PCNs, R-PCPHs and R-PCBBs in fish from a pulp-mill recipient watercourse

Pike, perch and lake bream from the river Kymijoki were analyzed by gas chromatography/mass spectrometry (GC/MS) for toxic polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs), hexachlorinated naphthalenes (HxCNs), non-ortho substituted polychlorinated biphenyls (coplanar PCBs) and alkylchloroaromatics of pulp mill origin. In most fish, the only congener of PCDD/PCDFs found was 2,3,7,8-TeCDF (< 2–12 pg/g in fresh weight [fw]). Traces of HxCNs (4–12 pg/g fw) were detected in all fish. Of coplanar PCBs, only PCB 77 (8–73 pg/g fw) and PCB 126 (2–5 pg/g fw) were detected. Alkylchlorophenanthrenes (C 4-PCPHs; P = 1–4), alkylchloronaphthalenes (C 2- and C 3-PCNs; P = 1–2) and alkylchlorobibenzyls (C 5-PCBBs; P = 1–4), were non-detectable (< 5 pg/g fw) in most fish. Polychlorinated diphenyl ethers (PCDEs), impurities of chlorophenol formulations, instead, were detected in these fish at several tens of ng/g in lipid.

13C NMR spectroscopic study of diphenyl ether and 28 of its polychlorinated derivatives

AbstractThe 13C NMR chemical shifts and coupling constants for diphenyl ether and 28 environmentally interesting polychlorinated diphenyl ethers were measured and analysed.

Polychlorinated diphenyl ethers—A review

Polychlorinated diphenyl ethers (PCDEs) have been identified as by‐products formed in the synthesis of chlorinated phenols. Analytical surveys have shown that PCDE residues are present in sediments, fish, wildlife, and human tissues. The uptake and persistence of PCDEs in laboratory animals resembled that observed for the polychlorinated biphenyls (PCBs), however, in metabolic studies, ortho hydroxylation of the PCDEs was the dominant oxidative pathway. Studies indicate that PCDE congeners elicit a broad spectrum of toxic and biochemical responses in laboratory animals including the induction of several cytochrome P‐450‐dependent monooxygenase enzyme activities. In contrast with the coplanar PCBs which are significantly more toxic than their monoortho coplanar analogs, the coplanar PCDE congeners and their monoorthochloro‐substituted analogs were equipotent. These data suggest that the PCDEs may contribute significantly to the toxicity of halogenated aromatics associated with chlorinated phenol‐derived contaminated areas such as toxic chemical waste dumpsites.

ChemInform Abstract: Photochemistry of Irgasan‐Triflate: A Simple Conversion of an Aromatic Hydroxyl Group to Chlorine in the Synthesis of Polychlorinated Diphenyl Ethers and Polychlorinated Dibenzofurans.

AbstractSeveral chlorophenoxy phenols, e.g. (I), are converted to their triflates, e.g. (III), (VI), which undergo triplet‐sensitized photolytic cyclizations in acetone to give chlorodibenzofurans, e.g. (IV), or singlet state substitution reaction in CCl4 saturated with Cl2 gas to give the corresponding chlorine substituted diphenyl ethers, e.g. (V), (VII).

Immunosuppressive and monooxygenase induction activities of polychlorinated diphenyl ether congeners in [formula omitted] mice: Quantitative structure-activity relationships

The dose-response effects of several polychlorinated diphenyl ether (polyCDE) congeners on the inhibition of the splenic plaque-forming cell (PFC) response to sheep red blood cell antigen and the induction of hepatic microsomal aryl hydrocarbon hydroxylase (AHH) and ethoxyresorufin O-deethylase (EROD) activities were determined in male C57BL 6 mice. The immunotoxic potencies for the polyCDE congeners (ED50 values for the suppression of PFCs/spleen and PFCs/10 6 cells) followed the order 2,3,3′,4,4′,5-hexaCDE (0.5 and 2.2 μmol/kg)> 3,3′,4,4′,5-pentaCDE (8.8 and 5.1 μmol/kg) > 2,3′,4,4′,5-pentaCDE (21.8 and 14.2 μmol/kg) > 3,3′,4,4′-tetraCDE (50.6 and 28.7 μmol/kg) > 2,2′,4,4′,5,5′-hexaCDE (81.2 and 56.5 μmol/kg) > 2,2′,4,5,5′-pentaCDE (258 and 228 μmol/kg) > 2,2′,4,4′,5,6′-hexaCDE (>400 μmol/kg for both responses). The potencies of the polyCDE congeners as inducers of hepatic microsomal AHH and EROD activities were similar to their immunotoxicities and only one compound, namely, 2,3′,4,4′,5,5′-hexaCDE, did not cause dose-response immunosuppressive effects in the mice. The structure-activity relationships for the polyCDEs exhibited both differences and similarities. For example, the coplanar 3,3′,4,4′-tetraCDE and 3,3′,4,4′,5-pentaCDE congeners were less immunotoxic than their monoortho 2,3′,4,4′,5-pentaCDE and 2,3,3′,4,4′,5-hexaCDE analogs, respectively, and similar results were also observed for their enzyme induction potencies. For the corresponding polychlorinated biphenyls (PCB) congeners the coplanar compounds were significantly more active than their monoortho analogs. In addition, two diortho-substituted compounds, namely, 2,2′,4,5,5′-pentaCDE and 2,2′,4,4′,5,5′-hexaCDE, were also immunotoxic at a dose of 400 μmol/kg whereas, their PCB analogs were inactive. These studies clearly demonstrate that for the polyCDE congeners, increasing ortho-chloro substitution is less effective in reducing the activity of these congeners compared to the well-recognized ortho effects reported for the PCBs. The differences in the structure-activity relationships between polyCDEs and PCBs are related to the ether bridge in the polyCDEs in which the resultant increased bond length beweeen the two phenyl rings thereby diminishes the effects of ortho substituents on the biochemical and toxic potencies of these compounds.

Determination of the prevalence of polychlorinated diphenyl ethers (PCDPES) in human adipose tissue samples

The HRMS analysis of human adipose tissues for PCDDs and PCDFs demonstrated responses representative of polychlorinated diphenyl ethers (PCDPEs). The responses correspond to hexathrough decachloro PCDPE isomers with lipid-based concentrations ranging as high as 2000 pg/g. The identification of the responses as PCDPEs is described, and estimates of residue levels are provided.

Photochemistry of irgasan-triflate: A simple conversion of an aromatic hydroxyl group to chlorine in the synthesis of polychlorinated diphenyl ethers and polychlorinated dibenzofurans

Several chlorophenoxy phenols were converted to their triflates by reaction with trifluoromethanesulfonyl chloride. The trifilates undergo triplet seneltlzed photolytic cyclizations at 300 nm in acetone to give chlorodibenzofurans or singlet state substitution reactions in carbon tetrachloride saturated with chlorine gas to give the corresponding chlorine substituted diphenyl ethers. 2-Chloro-3-hydroxy dlbenzofuran was similarly converted to the 2,3-dichlorodibenzofuran. The mechanism for displacement of triflate by chlorine appears to involve chlorine-arene π complexation.

Dioxins and other planar polychloroaromatic compounds in Baltic, Finnish and Arctic Fish samples

Polychloroaromatic compounds were analyzed with GC/MS in Baltic salmon, cod liver fat from the Arctic coast of Norway (Vestertana) and fish from Lake Kernaala in South Finland. Total PCBs in salmon and in cod liver fat were at backround levels (140–270 and 700–900 ng/g, respectively). Fish in Kernaala were heavily polluted by PCB (6000–14000 ng/g). PCDDs and PCDFs in the present samples were below 5 pg/g except 2,3,7,8-tetra-CDF, which was found 5–9 pg/g in Kernaala fish. In salmon, five different polychlorinated diphenyl ethers were found 5–19 pg/g, polychloronaphthalenes 0.1–12 ng/g and heptachlorofluorenones 0.1–7 ng/g. The extremely toxic coplanar PCBs were found in all samples: 3,3′,4,4′-tetra-CB 70–900 pg/g and 3,3′,4,4′,5-penta-CB 30–300 pg/g.

Induction of rat hepatic monooxygenase activity by polychlorinated diphenyl ethers

Polychlorinated diphenyl ethers are recognized environmental contaminants. Twelve of these compounds were tested for their ability to induce liver cytochrome P-450 and monooxygenase activities in Sprague-Dawley rats. All the compounds increased P-450 levels or increased monooxygenase activities in a manner resembling 3-methylcholanthrene, phenobarbital or a combination of both (mixed). The responses obtained resembled those of the polychlorinated biphenyls, some of which are known to be toxic.

Occurence and fate of polychlorinated aromatic ethers (PCDE, PCA, PCV, PCPA and PCBA) in environment

Analyses of aromatic chloroethers in salmon (Salmo salar), white-tailed eagle (Hailaetus albicilla) and fish liver oil have been performed by improved clean up method which separates polychlorinated diphenyl ethers (PCDEs), anisoles and veratroles (PCAs and PCVs), phenoxy anisoles and biphenyl anisoles (PCPAs and PCBAs), dioxins and dibenzofurans (PCDDs and PCDFs) to different fractions, respectively. Compounds from all these substance groups were detected and many of them identified with authentic model compounds.