Quantitative relationships between molecular structures, environmental temperatures and octanol-air partition coefficients of polychlorinated biphenyls

A quantitative model that incorporates information on both environmental temperatures (T) and molecular structures, for logarithm of octanol-air partition coefficient to base 10 (logK_OA) of polychlorinated biphenyls (PCBs) was developed. Partial least squares (PLS) analysis together with 16 theoretical molecular structural descriptors was used to develop the Quantitative relationships between structures, environmental temperatures and properties (QRSETP) model. The cross-validated Q_cum² value for the optimal QRSETP model is 0.976, indicating a good predictive ability for logK_OA of PCBs at different environmental temperatures. T, E_LUMO (the energy of the lowest unoccupied molecular orbital), molecular size or average molecular polarizability (α), and the net atomic charges on chlorine, hydrogen and carbon atoms of PCB molecules, are major factors governing logK_OA. The lower the E_LUMO, the greater the intermolecular interactions between octanol and PCB molecules, and thus the greater the logK_OA values. Because of intermolecular dispersive forces, the more chlorine atoms in PCB molecules, the greater the molecular size or α, the greater the logK_OA. The largest negative net atomic charge on a carbon atom (q_C^-) and molecular size or average molecular polarizability (α) are major factors governing temperature dependence of logK_OA. PCB molecules with low q_C^- values and more chlorines (big size or α) tend to have strong temperature dependence, due to intermolecular electrostatic interactions and dispersive forces, respectively.