title: Density functional theory study of semiquinone radical anions of polychlorinated biphenyls in the syn- and anti-like conformation.
abstract: Polychlorinated biphenyls (PCBs) can be metabolized to reactive metabolites, such as PCB semiquinone radical anions (SQ(•-)), whose structure and role in PCB-induced toxicity are difficult to investigate due to their relative instability. The unrestricted UB3LYP/6-311G** method was used to investigate several molecular descriptors of the syn- and anti-like conformation of SQs(•-). The bond lengths and angles of the quinone moiety of the SQs(•-) were in between the values reported for PCB quinones and hydroquinones, which is consistent with the distribution of the α highest occupied molecular orbital (α-HOMO). The dihedral angles between the two ring systems increased in the presence of ortho chlorine substituents and were smaller compared to the corresponding PCB quinones. The ground-state energies indicate that the anti-like conformation of the SQs(•-) is more favorable than the syn-like conformation. Molecular descriptor used for modeling of quantitative structure-activity relationships displayed some dependence on the conformation. These findings suggest that SQs(•-) in both the syn- and antilike conformation may interact differently with target molecules, which may have implications for the toxicity of PCBs.
authors.affiliation: Department of Chemical and Materials Engineering, University of Kentucky, Lexington, Kentucky 40506-0046, United States.
authors.forename: Jyothirmai
authors.initials: J
authors.lastname: Ambati
authors.forename: Yang
authors.initials: Y
authors.lastname: Song
authors.forename: Stephen E
authors.initials: SE
authors.lastname: Rankin
authors.forename: Hans-Joachim
authors.initials: HJ
authors.lastname: Lehmler
mesh_terms: D016227:Benzoquinones / Q000737:chemistry*; D004058:Diffusion; D008958:Models, Molecular; D008968:Molecular Conformation; D011078:Polychlorinated Biphenyls / Q000737:chemistry* / Q000633:toxicity; D021281:Quantitative Structure-Activity Relationship; D011789:Quantum Theory; D013237:Stereoisomerism
chemical_list: D016227:Benzoquinones; C025232:semiquinone radicals; D011078:Polychlorinated Biphenyls