Investigation On The Identification And Environmental Behavior Controlling Of PBDEs Through The Quantum Chemical Calculation And QSAR Model

Polybrominated diphenyl ethers (PBDEs), a group of brominated flame retardants (BFRs) consisted with 209 congeners, have been extensively used as fire retardant in textiles, circuit board, plastic, electronic appliances since 1960s. Mixed and not been chemically bound with the polymers, PBDEs can release to the environment easily in processes of production, usage and abandonment along with these polymers. Previous studies have shown that PBDEs have significant persistence, biological toxicity, long distance mobility and bioaccumulation in natural environment, so they were designated as persistent organic pollutants (POPs) in 2009, whose biological toxicity, potential endocrine disrupting and carcinogenicity were most concerned. However, previous studies were limited to certain representative congeners or certain POPs character because of less experimental data. Therefore, quantum chemical calculation and the quantitative structure-activity relationship model (QSAR) were used to supplement environmental behavior data of PBDEs in this paper. Firstly, biological toxicity was selected as pointcut and the biological toxicity level of each PBDE was evaluated; then the corresponding molecular vibrational spectra informations with significance with biological toxicity were abstracted and the relative identification research was carried out, forming theoretical tool to predict biological toxicity of PBDEs based on molecular vibration spectra; at last, environmental behavior controlling research of PBDEs was implemented from views of designing new environment-friendly flame retardant (the control of 4 POPs charactes simultaneously) and photodegradating existing congeners.In this paper,209 PBDE congeners were selected as target pollutants, and the binding affinity to the aryl hydrocarbon receptor binding (RBA) was as the index of biological toxicity. Then, the QSAR for RBA of PBDEs was established to predict RBA and toxicity level of each congener which was used to analyze biological toxicity mechanism. According to the established QSAR model, only BDE-85 possesses high biological toxicity level, and 13 PBDEs have medium level. We can conclude that:the effect sequence of different positions on the PBDEs’biological toxicity was: ortho>para>meta; the introduction of ortho-substituents can weaken the biological toxicity of PBDEs significantly, and para-substituents present another extreme; non-covalent intermolecular interactions are very important for determining the relative position and the strength of the binding affinity between the receptor and the ligand.Based on the biological toxicity level of each congener, the molecular vibrational spectra informations with significant correlation with high/medium biological toxicity were abstracted and the congeners with high/medium biological toxicity level and most widerspread ones were selected as typical PBDEs for further identification research via characteristic vibrational frequencies and spectra region. At last, the enhancing effect of organic solvents on vibrational intensity of PBDEs’ molecular vibrational spectra was analysed from view of solvantion effect. By screening, C-O stretching vibration and triangle breathing vibration are assigned as typical vibration, and we can distinguish 23 kinds of PBDEs via frequencies of C-O stretching vibration in Raman spectra of PBDEs. Meanwhile, the frequencies of triangle breathing vibration of IR spectra can be used to evaluate the biological toxicity level of PBDEs and the spectrum region of C-O stretching vibration is beneficial to grouping congeners with different toxicity level. Solvation effect might have significant enhancing effect on vibration intensity and frequency dispersity of PBDEs which is conducive to identify PBDEs, and the most significant solvent is DMSO.For the first aspect, the pharmaophore model and the full factor experimental design were both used to explore and form the regulator scheme for four POPs characters of PBDEs. Then, the performances of modified congeners were evaluated from views of four POPs characters and flammability to verify the reasonability and universality of established modified scheme for PBDEs. From the established pharmacophore models for 4 POPs characteristics of PBDEs we can see, the hydrophobic feature plays the most important role for all POPs characters. Among these hydrophobic groups, ethyl and propyl show the most significant regulation effect on POPs characters; on the contrary, nitro and hydroxyl groups show increasing effect. The introduction of hydrophobic substituent can show good modified effect on POPs characters, especially for biological toxicity (redue 70.60%) and long distance migration (redue 70.88%). Meanwhile, the modified congeners also have the similar flame retardant performance with PBDEs.For the second aspect, photodegradability and photodegradation rate of 209 PBDEs were analysed systematically (relation with substituent characters) firstly, then the solvation effect on photodegradation characters and promoting mechanism of PBDEs’ two photodegradation reactions in organic solvents were analysed. The photodegradation of PBDEs was mainly regulated by factors of total substituent number, substituent number in ortho-position and dispersibility of substituents; tetrahydrofuran and chloroform can make the photodegradability of PBDEs easily by solvation effect which is main caused by the photoreaction between excited PBDEs and solvent molecules; the easiest reaction between PBDEs and OH is addition reaction, which can be enhanced by organic solvents via narrowing the energy barrier and increasing the reaction heat.