Experimental And Theoretical Study On The Environment Properties Of Some Halodiphenyl Ethers And Their Analogues

Halogenated diphenyl ethers involve polyfluorinated diphenyl ether (PFDE), chlorinated diphenyl ether (PCDE), brominated diphenyl ether (PBDE) and iodinated diphenyl ethers (PIDE). Previous studies mainly focused on PBDE and PCDE, which widely existed in the environment. They enriched and produced toxicity in organisms, and could be degraded via reduction, lighting, or biological metabolisms, producing debrominated products, hydroxylated and methoxylated analogues. Many gaps still exist in studies on diphenyl ethers still now. For example, their oxidative degration mechanisms, the natural environmental factors affecting their toxicity and degradation, and the physicochemical properties of hydroxylated and methoxylated analogues, are all unknown. Studies on PFDE and PIDE are scarce. As a result, some work was carried out around the above points with both experimental and theoretical methods. It is expected to be helpful in deepening the understandings on diphenyl ether derivatives. Concrete studies consist of the following five aspects:(1) BDE209is water-insoluble, and its oxidation in organic solvent will be strongly interfered by oxidation of solvent itself. So its oxidation mechanism is still unknown. It was found in this study that BDE209could be oxidized effectively by potassium permanganate (KMnO4) in sulfuric acid medium. A total of fifteen intermediate oxidative products were detected and two reaction pathways were proposed. Cleavage of the ether bond was a crucial oxidative manner, and direct oxidation on the benzene ring also played an important role. Hydroxylated nonabromodiphydyl ether was produced. The chronological order in which product concentrations reached peaks was consistent with which in the proposed pathway. The density function theory (DFT) calculation results complemented and verified the proposed reaction pathway very well. In addition, the degradation reaction fitted pseudo-first order rate kinetics when oxidant was excess. Increasing acid content and temperature would promote the reaction.(2) We investigated and compared influences of decabromodiphenyl ether (BDE209) in different concentrations on soil urease, CAT and alkaline phosphatase (ALP) activities in dark and in sunlight/dark (12h/12h) condition respectively. Then we introduced Mataphire guillelmi and Lolium perenne L respectively and observed their interference on the damage of the soil microbial communities. In addition, the influences of BDE209on oxidant/antioxidant responses (superoxide dismutase SOD, catalase CAT and malondialdehyde MDA) of metaphire guillelmi and Lolium perenne L were investigated. Results showed that BDE209brought more significant damage to soil in dark than in the light. The metaphire guillelmi could weaken the toxicity, while Lolium perenne L rarely interfered despite its assistance in improving soil enzyme activities. Damages on metaphire guillelmi and Lolium perenne L were serious in500mg/kg group, and it would be bigger with a longer time in lower concentration groups.(3) Hydroxylated and methoxylated analogues of diphenyl ethers are generally regarded as important degradation products of halogenated diphenyl ether. The octanol-water partition coefficient (logKow) and organic carbon-based sorption coefficients (logKoc), are crucial to estimate the environmental fate of a chemical. Some representative polymethoxylated diphenyl ethers (PMeODEs), polyhydroxylated diphenyl ethers (POHDEs), methoxylated polychlorinated diphenyl ethers (MeO-PCDEs) and hydroxylated polychlorinated diphenyl ethers (OH-PCDEs) were synthesized and their logKow and logKoc values were determined. QSPR models on the properties of PMeODEs and POHDEs were established using structural and substituent descriptors respectively. As to PMeODEs and PMeODEs, the properties were negatively correlated to mean polarizability (α) and positively correlated to the ability to give electron. The increasing substituent number would decrease logKow and logKoc, while meta-substituents would increase them slightly. The logKow and logKoc of MeO-PCDEs and OH-PCDEs were positively correlated with a but negatively correlated with the ability to accept electron. In brief, the properties influencing logKow and logKoc are mainly electronic. All the models had good robustness and predictivity. In addition, linear relationships existed between logKow and logKoc for the four series of chemicals, and the logKows of either PMeODEs or POHDEs were negatively correlated to those of PCDEs.(4) As studies on PFDE and PID are scarce, and we want to examine the toxicity differences brought by different halogens, we determined LD50s of4,4’-PFDE,4,4’-PCDE,4,4’-PBDE,4,4’-PIDE to ICR female mice and determined their acute toxicity order as4,4’-PIDE<4,4’-PFDE<4,4’-PCDE≈4,4’-PBDE. The QSAR results on LD50showed that the toxicity was negatively correlated to the octanol-water partition coefficient (log-Kow).All chemicals brought bigger damage to liver than to kidney, and caused hapatic pathogenic change. The oxidant/antioxidant responses (SOD, CAT and MDA) of mice under lower concentrations and28-day administration reflected the same toxicity order as acute toxicity. The test results on halogenated benzenes were quite similar with those on diphenyl ethers, while results on halogenated phenols were different.(5) Intramolecular hydrogen bonds would form in polyhydroxylated compounds, and influenced their properties. Polyhydroxylated dibenzofurans (POHDF) could be produced during photodegradation of halogenated diphenyl ethers, and had much bigger toxicity than polyhydroxylated diphenyl ethers. Four types of intramolecular hydrogen bonds (between a hydroxyl and the oxygen atom in the matrix, between ortho hydroxyls, between the oxygen of hydroxyl at position1and the hydrogen of the matrix at position9, and between hydroxyls at positions1and9) could be fromed in POHDF, and their energies were ascertained by comparing standard Gibbs energy of formation (ΔfG(?)) of configurational isomers as approximately8-11kJ/mol,16-21kJ/mol,5-8kJ/mol and23-25kJ/mol, respectively. The bond energies were verified by an experiment and the entrance geometry on main paths. The stable conformations were thus ascertained. Good QSPR models on their thermodynamic properties (standard state entropy S(?), standard enthalpy of formation AfH(?) and AfG(?)) and logKow were established with the number and position of hydroxyl as descriptors. Increasing substituent number would enhance the molecular stability and hydrophily, and substituent position also affected the properties because of the hydrogen bonds. Isomers with the fourth type of hydrogen bond are most likely to form thermodynamically. Influences of hydrogen bond on ionization were also investigated and the first-order ionization constant (pKa1) for each conformation was obtained.