Polychlorinated dibenzofUrans structures

Loonen, H., M. Tonkes, J.R. Parsons, and H.A.J. Govers. 1994b. Bioconcentration of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans in guppies after aqueous exposure to a complex PCDD/PCDF mixture relationship with molecular structure. Aquai. Toxicol. 30 153-169. 

Fig. 7 Generic chemical structures of polyhalogenated compounds. X=C1, Br. (I) Polychlorinated biphenyls (PCBs), polybrominated biphenyls (PBBs) (II) chlorophenols (CPs), bromophenols (BPs) (III) polychlorinated diphenyl ethers (PCDE), polybrominated diphenyl ethers (PBDE) (IV) polychlorinated dibenzo-p-dioxin (PCDD), polybrominated dibenzo-p-dioxin (PBDD) (V) polychlorinated dibenzofuran (PCDF), polybrominated dibenzofuran (PBDF) (VI) tetrabromobisphenol A (TBBPA)...

Dioxins are a particular group of chlorinated organic molecules which have been associated with pulp and paper production and are a concern because of their extreme toxicity. There are two groups of molecular types which fall into the general category referred to as dioxins. These are the polychlorinated dibenzodioxins (PCDDs) and the polychlorinated dibenzofurans (PCDFs). The structures of these molecules are shown in Figure 10.4. 

Figure 10.4 The structures of polychlorinated dibenzodioxins and polychlorinated dibenzofurans...

Polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans and ortho-unsubstituted polychlorinated biphenyls (non-ortho polychlorobiphenyls) are three structurally and toxicologically related families of anthropogenic chemical compounds that have in recent years been shown to have the potential to cause serious environmental contamination due to their extreme toxicity [77-82], These substances are trace-level components or byproducts in several large-volume and widely used synthetic chemicals, principally polychlorobiphenyls and... 

When PCBs burn, polychlorinated dibenzofurans (PCDFs) are among the products that may form. Examine the structure shown below, and circle and name the functional groups. 

For halogenated aromatic hydrocarbons like polychlorinated biphenyls (PCBs), polychlorinated dibenzofurans (PCDFs), and polychlorinated dibenzo-p-dioxins (PCDDs) the binding to the aryl hydrocarbon (Ah) receptor regulates their toxicity [89]. The Ah receptor controls the induction of one of the cytochrome P450 enzymes in the liver. Toxic responses such as thymic atrophy, iveight loss, immu-notoxicity and acute lethality are associated ivith the relative affinity of PCBs, PCDFs and PCDDs for the Ah receptor [89]. The quantitative structure-activity relationship (QSAR) models predicting the affinity of the halogenated aromatic hydrocarbons ivith the Ah receptor describe the electron acceptor capability as well as the hydrophobicity and polarizability of the chemicals [89[. 

In several tests on compound sets that are structurally very different from the training set, including a larger set of pesticide molecules, Eq. (10.3) proved to be very robust and transferable. Recently, the method was applied to polychlorinated dibenzo-/)-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) [137]. As shown in Fig. 11.3. it was found that the COSMO-RS predictions appear to be even more accurate than the experimental data, especially at the low-solubility end. While the experimental results for many compounds show a scatter of more than a... 

Fig. 8.2 Structures of polychlorinated dibenzo-p-dioxin, polychlorinated dibenzofuran and polychlorinated biphenyl.

As polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs) are compounds with similar structures and monitoring methods, they are discussed together in this chapter. The structures of PCDDs, PCDFs, PCBs, and PBDEs are shown in Fig. 4.1. 

Polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs) have attracted considerable attention in recent decades, owing to concern over their potential adverse effects in humans and wildlife, which are compounded by their ubiquitous environmental presence and resistance to degradation. Amongst the 75 possible PCDDs, 135 PCDFs and 209 PCBs, there exists wide variation in physicochemical properties, bioaccumulative tendencies and toxicity. Figures 1 and 2 illustrate the basic structures and nomenclature of both PCDDs, PCDFs collectively referred to as PCDD/Fs-and PCBs. 

Hileman FD, Hale MD, Mazer T, Noble RW (1983), Chemosphere 14 601-608.. .Synthesis of polychlorinated dibenzofurans with confirmation by molecular structure/gas chromatographic retention relationships"... 

Quantitative structure-retention relationships (QSSRs) have been established for polychlorinated dibenzofurans to assist their determination by gas chromatography (GC) <2002MI7, 2003ANC1049, 2005MI1683>. 

Arulmozhiraja A, Morita M. Structure-activity relationships for the toxicity of polychlorinated dibenzofurans Approach through density functional theory-based descriptors. Chem Res Toxicol 2004 17 348-56. 

Structure can be observed by the loss of dioxin-like activities of PCBs with ring substitution(s) at one or more of the ortho (2,2 6,6 -) position(s) which can lead to distortion from planar structure. Subsequent AhR binding data indicated that polychlorinated dibenzofuran congeners have binding activity similar to that of their dibenzo-p-dioxin counterparts (Woo and Lai 2003). 

Fig. 2 Molecular structures of the Dirty Dozen. 1 - Polychlorinated dibenzo-p-dioxines, PCDD 2 - Polychlorinated dibenzofuranes, PCDF 3 - Polychlorinated biphenyls, PCB 4 - Hexachlorobenzene, HCB 5 - 2,2-Bis(4-chlorophenyl)-l,l,l-trichloroethane, DDT 6 - Toxaphene 7 - Aldrin 8 - Dieldrin 9 - Endrin 10 -Chlordane 11 - Heptachlor 12 - Mirex.

Figure 31.1 Molecular structures of (a) polychlorinated dlbenzo-p-dloxlns (PCDDs) (b) polychlorinated dibenzofurans (PCDFs) and (c) polychlorinated biphenyls (PCBs). Numbers Indicate positions on the basic structure of the molecules where chlorine substitutions can take place, m, meta o, ortho p, parapositlon.

Dioxin is a term used to describe a large group of chemical compounds having a similar basic structure. The most common subgroup of dioxin compounds (of which there are 75 different varieties) comprises those which include chlorine atoms. A few are toxic the most toxic is 2,3,7,8-tetrachlorodibenzo(para) dioxin (2,3,7,8-TCDD). There are also 135 polychlorinated dibenzofuran corrtpotmds, known as furans. ... 

Polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs) are chemically classified as halogenated aromatic hydrocarbons. The chlorinated and brominated dibenzodioxins and dibenzofurans are tricyclic aromatic compounds with similar physical and chemical properties, and both classes are similar structurally. Certain of the PCBs (the so-called coplanar or mono-ortho coplanar congeners) are also structurally and conformationally similar. The most widely studied of these compounds is 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). This compound, often called simply dioxin, represents the reference compound for this class of compounds. The structure of TCDD and several related compounds is shown in Figure 4.1. 

B. ifeys and S. Safe, Polychlorinated dibenzofurans (PCDFs) effects of structure on binding to the 2,3,7,8-TCDD cytosolic receptor protein, AHH induction and toxicity, Toxicol. 32 131 (1984). 

Isomerization and dechlorination reactions have been implicated in the metabolism of HCBPs (McKinney, 1976 Hutzinger a/., 1974). However, identification of potentially toxic dibenzofuran structures in some metabolites, and lower ratios of PCBs to polychlorinated dibenzofiirans in liver compared to adipose tissue, have caused concern regarding the metabolic formation and accumulation of PCDFs in the liver (Kuratsune etal, 1976). Further work in this area is essential. Figure 9.5 lists the various metabolites identified in mammalian metabolism involving different species. 

The CD polymers can remove organic pollutants from water at parts per trillion levels. These polymers can be recycled at least 18 times without loss of their high adsorption efficiency. However the prolonged recycling destroys often their structural integrity and some loss of polymer mass was observed. In order to overcome these difficulties, small amounts (<5%) of multiwall carbon nanotubes (MWNTs) were added to polymers. It is known that carbon nanotubes are able to efficiently adsorb biphenyls, dioxins and polychlorinated dibenzofurans, while remaining chemically inert, but they are too expensive for removal of these water pollutants. However, carbon nanotubes may be used in combination with CD polymers. 

Fig. 1. Structures of polycyclic compounds, (a) Polychlorinated (brominated) biphenyl (b) Polychlorinated (o-, m-, p-) terphenyl (c) Polychlorinated naphthalene (d) Polychlorinated dibenzofuran...

Toxic and other interaction effects of PCDDs with other groups of polychlorinated chemicals having similar structure and properties, such as biphenyls, dibenzofurans, and biphenylenes. 

Beger, R.D., Buzatu, D.A. and Wilkes, J.G. (2002) Combining NMR spectral and structural data to form models of polychlorinated dibenzodioxins, dibenzofurans, and biphenyls binding to the AhR. Journal of Computer-Aided Molecular Design, 16, 727-740. 

Polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) are two series of tricyclic aromatic compounds which exhibit similar physical and chemical properties. Some of these compounds have extraordinary toxic properties and were the subject of much concern. They have been involved in accidents like the Yusho accident in Japan 1968 l 9 the intoxication at horse arenas in Missouri, USA in 1971 (2.) and the accident near Seveso, Italy in 1976 (3.). The chemical structures and the numbering of these hazardous compounds are given below. 

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