Quantitative relationships between molecular structures, environmental temperatures and octanol-air partition coefficients of PCDD/Fs

A concise quantitative model that incorporates information on both environmental temperature (T) and molecular structures, for logarithm of octanol-air partition coefficient (K_OA) to base 10 (logK_OA) of PCDDs, was developed. Partial least squares (PLS) analysis together with 14 quantum chemical descriptors were used to develop the quantitative relationships between structures, environmental temperatures and properties (QRSETP) model. It has been validated that the obtained QRSETP model can be used to predict logK_OA of other PCDDs. Molecular size, environmental temperature (T), q⁺ (the most positive net atomic charge on hydrogen or chlorine atoms in PCDD molecules) and E_LUMO (the energy of the lowest unoccupied molecular orbital) are main factors governing logK_OA of PCDD/Fs under study. The intermolecular dispersive interactions and thus the size of the molecules play a leading role in governing logK_OA. The more chlorines in PCDD molecules, the greater the logK_OA values. Increasing E_LUMO values of the molecules leads to decreasing logK_OA values, implying possible intermolecular interactions between the molecules under study and octanol molecules. Greater q⁺ values results in greater intermolecular electrostatic repulsive interactions between PCDD and octanol molecules and smaller logK_OA values.