DFT study on the bromination pattern dependence of electronic properties and their validity in quantitative structure–activity relationships of polybrominated diphenyl ethers

With quantum chemical computation of density functional theory (DFT), the electronic properties including the polarisabilities, polarisability anisotropies and quadrupole moments of a total of 209 congeners of polybrominated diphenyl ethers (PBDEs) were evaluated. The electronic properties were shown to be highly dependent on the bromination pattern, i.e. their values changed sensitively with the number and sites of bromination. Being similar to the 2,3,7,8-, 1,4,6,9-chlorination of dioxins, respectively, 3,3',4,4'-, 2,2',5,5'-bromination of PBDEs can impose relatively greater effects on the electronic properties. Some of electronic properties were found to be potent in explaining the variance of toxicity, and the potency was verified by the development of quantitative structure-activity relationships (QSARs). To further improve the stability and predictability of QSARs for toxicity, two-dimensional topological indices were introduced. In QSARs, polarisability anisotropy was more significant than other polarisability tensors, indicating the implicit occurrence of dispersion interaction between the ligand and aryl hydrocarbon receptor (AhR). For PBDEs, the quadrupole moment was as significant as shown previously for dioxins. As interesting descriptors with encoded information about dispersion and electronics, the electronic properties analysed herein are helpful in obtaining a better understanding of the congener-specific toxicities of PBDEs, and are applicable and may be extended to research into the toxicology of structurally similar compounds, such as halogenated aromatics.