Chlorine Substitution Pattern, Molecular Electronic Properties, and the Nature of the Ligand−Receptor Interaction: Quantitative Property−Activity Relationships of Polychlorinated Dibenzofurans

It was confirmed that both quadrupole moments and polarizabilities of polychlorinated dibenzofurans (PCDFs), which were calculated using Hartree-Fock theory and/or density functional theory, change systematically with the chlorination pattern governing molecular charge distribution. A mathematical model based on ligand-receptor binding and solute-solvent interaction is reported to explain the difference in toxicity between PCDFs. Multiple regression analysis demonstrated that the difference in the potency of aryl hydrocarbon hydroxylase (AHH) and 7-ethoxyresorufin O-deethylase (EROD) inductions is mostly determined by the polarizabilities of PCDFs. This suggests that the interaction of a PCDF with the aryl hydrocarbon receptor (AhR) and its interaction with surrounding molecules in the cytosol are dispersion interactions rather than electrostatic interactions. Quadrupole moment, electron affinity, and absolute hardness do not appear to be significantly correlated with the differences in AHH and EROD activities among PCDFs. The entropy change of dissolution is important in predicting the AHH and EROD activities with good accuracy. A mathematical model is also used to study the differences in AhR binding between PCDFs.