QSPR On Octanol/Water Partition Coefficient Of Selected Herbicides

The n-octanol/water partition coefficient (K_OW) of organic chemicals is an importantparameter to characterize their environmental behavior and biological activity, which canreflect hydrophobic ability and environmental fate. Because the experimental determinationmethod is consuming and can't meet the need of ecological risk assessment, many researchersfocused on the development of estimating method based on calculated values. QuantitativeStructure-Property relationship plays an important role on predicting environmental behaviorparameter and explaining the transfer and transform of organic pollutants. This studyestablished QSPR model of K_OW values for selected herbicides and explained the partitioningmechanism for the further application of predicting K_OW values.This study calculated 18 kinds of theoretical molecular structural descriptors of 55s-triazine herbicides and phenylurea herbicides using PM3 arithmetic and established QSPRmodel of K_OW using partial least square (PLS) regression. Q_cum (the variance that can beinterpreted by the selected PLS components) is 0.726, indicating good predicting ability androbustness of the model. Connolly solvent-excluded volume (CSEV), Connolly molecular area(CMA), Connolly accessible area (CAA), molecular weight (Mw), electronic energy (EE), totalenergy (TE), dipole moment (μ) and the energy of the lowest-unoccupied molecular orbital(E_LUMO) are the primary molecular structural parameters determining logK_OW values.Molecule volume is the primary factor affecting the partition between n-octanol and water oforganic chemicals. The larger is the molecule volume; the easier is the partition to then-octanol phase. Polarity and charge transfer ability of the molecules are other acting factors.To further analyze the difference of the partition mechanism, models for two groups ofherbicides were also developed respectively and the performance of each model has beenimproved. Q_cum² of the s-triazine herbicides model is 0.871, and the primary factor ismolecule volume. For the phenylurea herbicides model, Q_cum² is 0.832, and molecule size andcharge transfer ability are dominating factors.