Prediction of octanol-air partition coefficients for PCBs at different ambient temperatures based on the solvation free energy and the dimer ratio.

Temperature-dependent octanol-air partition coefficients (K) are of great importance in assessing the environmental behavior and fate of persistent organic pollutants including polychlorinated biphenyls (PCBs). Due to the tremendous amounts of time, effort and cost needed for the experimental determination of K, it is desirable to develop a rapid and precise predictive method to estimate K just based on molecular structure. In the present study, a predictive model for log K of PCBs at ambient temperatures was developed based on the thermodynamic relationship between K and the solvation free energy from air to octanol (ΔG). For the calculation of ΔG of PCBs, the optimal combination of theoretical method and basis-set was identified to be HF/MIDI!6D for both geometry optimization and energy calculation. Dimer formation could affect the partition behavior and promote the apparent K values of PCBs. After taking the effect of dimer formation into account, the goodness-of-fit, predictive ability, and robustness of the predictive model were significantly improved. Apparent log K values of PCBs at different ambient temperatures ranging from 283.15 to 303.15 K were predicted. Compared with other reported models, the model developed in the present study had not only comparable goodness-of-fit and predictive ability, but also a universal application domain and the relative independency of experimental data. Therefore, the solvation free energy method could be a promising method for the prediction of K.