Estimation of n‐Octanol/Water Partition Coefficients (log KOW) of Polychlorinated Biphenyls by Using Quantum Chemical Descriptors and Partial Least Squares

The n-octanol/water partition coefficient (log KOW) is a useful parameter for the assessment of the environmental fate and impact of xenobiotic trace contaminants. Quantitative structure-activity relationship (QSAR) model for log KOW of polychlorinated biphenyls (PCBs) was analyzed by using the density functional theory at B3LYP/6-31G(d) level and the partial least squares (PLS) method with an optimizing procedure. A PLS model with reasonably good coefficient (R2=0.992) and cross-validation test (Q2cum=0.988) values was obtained. All the predicted values are within the range of ±0.3 log unit from the observed values. The log KOW values of 7 PCBs in the test set predicted by the model are very close to those observed, indicating that this model has high fitting precision and good predictability. The PLS analysis showed that PCBs with larger electronic spatial extent and lower molecular total energy values tend to be more hydrophobic and lipophilic