Modelling the octanol-air partition coefficient of aromatic pollutants based on the solvation free energy and the dimer effect

In this study, generalized predictive models were developed to estimate KOA of four kinds of aromatic pollutants based on the calculated solvation free energy and taking the dimer effect into account. Uncorrected log KOA values, which were directly estimated from the calculated solvation free energy of individual molecules, underestimated experimental values, and the deviation increased with increasing log KOA. Dimers were found to greatly affect the apparent KOA values of these aromatic pollutants, which were driven by 7C -7C interactions. London dispersion and exchange-repulsion terms were identified to be dominant components of the underlying 7C -7C interactions. It is interesting to find that the 7C -7C interactions of polybrominated diphenyl ethers correlate with not only the molecular polarizability but also the size of opposing aromatic surfaces, which leads to a different trend of 7C -7C interactions from other aromatic pollutants. A universal quantitative structure-activity relationship model was developed to estimate the proportion of dimers based on five molecular structural descriptors relevant to the 7C -7C interactions. After calibration with the dimer effect, estimations of log KOA were consistent with experimental values. Therefore, the dimer effect should be taken into consideration when investigating the partition behavior of aromatic pollutants, and the solvation free energy model could be an alternative method for the prediction of KOA.