Screening the partition behavior of a large number of chemicals with a quantum-chemical software.

For 8500 organic chemicals from the Canadian Domestic Substances List, air/water and octanol/water partition coefficients have been calculated with COSMOfrag a predictive a priori method based on quantum mechanics and statistical thermodynamics provided by COSMOlogic. The results were compared with predictions from the EPI Suite. On average a difference of 1.8 log units between both methods was observed for the predicted logK(aw) values. This has consequences for the classification in terms of atmospheric long range transport potential and bioaccumulation in the terrestrial food chain where 11% and 17% of all compounds were classified differently. Much better agreement was observed for the predicted logK(ow). Principal differences became obvious for compounds that occur as isomers or conformers. The modules of the EPI Suite are not designed to account for information on stereochemistry of molecules or E/Z isomers. Intramolecular H-bonds are only accounted for if specific correction factors exist from the calibration procedure. In contrast, COSMOfrag in combination with COSMOtherm can identify the existence of such isomers or H-bond conformers and account for these effects in the calculations.