Use of quantitative-structure property relationship (QSPR) and artificial neural network (ANN) based approaches for estimating the octanol-water partition coefficients of the 209 chlorinated trans-azobenzene congeners
Polychlorinated azobenzenes (PCABs) can be found as contaminant by products in 3,4-dichloroaniline and its derivatives and in the herbicides Diuron, Linuron, Methazole, Neburon, Propanil and SWEP. Trans congeners of PCABs are physically and chemically more stable and so are environmentally relevant, when compared to unstable cis congeners. In this study, to fulfill gaps on environmentally relevant partitioning properties of PCABs, the values of n-octanol/water partition coefficients (log KOW) have been determined for 209 congeners of chloro-trans-azobenzene (Ct-AB) by means of quantitative structure-property relationship (QSPR) approach and artificial neural networks (ANN) predictive ability. The QSPR methods used based on geometry optimalization and quantum-chemical structural descriptors, which were computed on the level of density functional theory (DFT) using B3LYP functional and 6–311++G** basis set in Gaussian 03 and of the semi-empirical quantum chemistry method (PM6) of the molecular orbital package (MOPAC). Polychlorinated dibenzo-p-dioxins (PCDDs), -furans (PCDFs) and -biphenyls (PCBs), to which PCABs are related, were reference compounds in this study. An experimentally obtained data on physical and chemical properties of PCDD/Fs and PCBs were reference data for ANN predictions of log KOW values of Ct-ABs in this study. Both calculation methods gave similar results in term of absolute log KOW values, while the models generated by PM6 are considered highly efficient in time spent, when compared to these by DFT. The estimated log KOW values of 209 Ct-ABs varied between 5.22–5.57 and 5.45–5.60 for Mono-, 5.56–6.00 and 5.59–6.07 for Di-, 5.89–6.56 and 5.91–6.46 for Tri-, 6.10–7.05 and 6.13–6.80 for Tetra-, 6.43–7.39 and 6.48–7.14 for Penta-, 6.61–7.78 and 6.98–7.42 for Hexa-, 7.41–7.94 and 7.34–7.86 for Hepta-, 7.99–8.17 and 7.72–8.20 for Octa-, 8.35–8.42 and 8.10–8.62 for NonaCt-ABs, and 8.52–8.60 and 8.81–8.83 for DecaCt-AB. These log KOW values shows that Ct-ABs are compounds of relatively low environmental mobility (log KOW > 4.5) and of significant bioaccumulation potential.