QSAR Models For The Prediction Of Physicochemical Properties Of Polybrominated Diphenyl Ethers

In recently years, quantitative structure activity relationship (QSAR) has beenwidely applied in the area of environmental chemistry, pharmaceutical chemistry andcomputational chemistry. This method is effective in the prediction of theenvironmental risk of organic chemicals, saving resources and reducing experiment.In this study, the QSAR of some intramolecular and intermolecular physicochemicalproperties of polybrominated diphenyl ethers (PBDEs) were investigated. On thebasis of quantum calculations, the relevant structural parameters were obtained toestablish QSAR models for the prediction of bioconcentration factor (BCF) and Kowand to explore theoretical indicators for the reductive debromination pathways ofPBDEs. In addition, the effects of bromine substitution on the molecular structure ofPBDEs were also evaluated. The main results are as follows:(1) Density functional theory (DFT) calculations were carried out at theB3LYP/6-31G*level for all selected PBDEs. The model of BCF and Kowweredeveloped based on a partial least square (PLS) method. Results suggested that thenumber of bromine substitution influenced BCF and Kowand no desirable modelscould be established using the parameters of logBCF and logKow. However, goodpredictions could be achieved in logBCF-NBrmodel, with the correlation coefficientfitting (R2Y (cum)) and cumulative effectiveness (Q2cum) being0.980and0.921,respectively. In the model of logKow÷NBr, the R2Y (cum)and Q2cumwere0.893and0.693.Both of the two models could successfully predict BCF and Kowvalues of PBDEs. Inaddition, ET, Re and NBrwere found to influence the model prediction.(2) The degradation of PBDEs in the environment was studied based on thestructural theoretical chemistry. The results showed that QBr (n)could be used topredict the debromination of PBDEs. The calculation results suggested that PBDEswith bromines at the para positions were difficult to be debrominated because theirQBr (n)values were relatively low. Once debrominated, the formation intermediateswere difficult to undergo further debromination. This model could successfullyexplain the debromination pathways of PBDEs. (3) The effects of bromine substitution on the dihedral angle (D) of the plane ofthe two benzene rings in PBDEs molecular were also analyzed. The results showedthat non-planar structure were relatively stable except when6,6’–postions in PBDEsare substituted by two bromine atoms. The substitution of bromine apparently causedthe torsion of the plane of PBDEs. According to the calculation of structuraltheoretical chemistry, θC-O-Cvalues of non-planar structure optimized PBDEs werelower, while RC1-O, RO-C1, RC6-H, RC6’-Hand μ were higher as compared with the planarstructure optimized PBDEs. The substitution of bromine altered D, but no directrelationship were observed between RC6-*, RC6’-*and D.