Estimation of K_OA values of 209 polychlorinated trans-azobenzenes by PM6 and DFT methods

Abstract

The octanol-air partition coefficients (K_OA) of all 209 PCt-ABs were determined computationally to fill gaps on their environmentally relevant physical and chemical properties. These properties have been determined using two computational approaches: the semi-empirical quantum chemistry method for property parameterization (PM6) of the molecular orbital package (MOPAC) and density functional theory (DFT) method using B3LYP functional and 6–311++G** basis set in Gaussian 03 software and artificial neural network (ANN) predicting abilities. Both computational methods enabled estimation of log K_OA partition coefficients of PCt-ABs with a similar accuracy and precision. The PM6 method compared to DFT was highly superior because it requires much less time, manpower and cost of hardware. The determined log K_OA values of the investigated PCt-ABs for standard condition (25°C) varied between 8.30 and 8.75 for Mono-; 8.71 and 9.92 for Di-; 9.58 and 10.72 for Tri-; 10.11 and 11.34 for Tetra-, 10.83 and 11.85 for Penta-; 11.24 and 12.36 for Hexa-; 11.87 and 12.66 for Hepta-; 12.31 and 12.97 for Octa-; 12.89 and 13.21 for Nona-Ct-ABs; and 13.17- and 13.49 for Deca-Ct-AB. PCt-ABs, in view of these log K_OA values, can be classified as compounds of relatively low (Mono-, Di- and some of Tri- Ct-ABs with values of log K_OA around 8 to 10) environmental mobility (most of Tri- to Nona-Ct-ABs and Deca-Ct-AB homologues with values of log K_OA >10), and with a potential to be adsorbed by soil particles.

Keywords:

• Octanol-air partition coefficients (K_OA)
• physical-chemical partitioning coefficients
• polychlorinated azobenzenes
• PCt-Abs
• herbicides
• POPs
• environmental chemistry
• environmental fate

Acknowledgments

Computations were carried out using computers in the TASK - Academic Computer Center in Gdańsk. This work in part was supported under grant no. DS/8130-4-0092-1.