(541b) Application of COSMO-RS Approximation to the Prediction of Physical Properties of Nitro-Compounds: Water Solubility
A number of studies have shown that nitro compounds, as well as their metabolites of environmental transformation, by-products of synthesis or incomplete combustion are harmful for the biosphere due to their toxicity. Therefore, remediation of these contaminants is a point of prominent concern for environmental science. The environmental fate of chemicals, as well as the efficiency of in-solution treatment is determined largely by their solubility in water. In particular, high water solubility (SW) leads to expeditious distribution in water, i.e. chemicals that rapidly and completely dissolve in water are transported along with the general water flow. Low SW is generally associated with high affinity for adsorption to solids in water (soil particles or sediment). In addition, high water solubility is associated with absorption of pollutants by living organisms. Hence, solubility of hazardous chemicals is one of the most fundamental physical properties of ecological importance.
Water solubility values for twenty seven nitro compounds with experimentally measured values were computed using the conductor-like screening model for real solvent (COSMO-RS) based on the density functional theory and COSMO technique. We have found that the accuracy of the COSMO-RS approach for prediction of water solubility of liquid nitro compounds is impressively high (the errors are lower than 0.1 LU). However, for some solid nitro compounds, especially nitramines, there is sufficient disagreement between calculated and experimental values. In order to increase the accuracy of predictions the quantitative structure?property relationship (QSPR) part of the COSMO-RS approach has been modified. The solubility values calculated by the modified COSMO-RS method have shown much better agreement with the experimental values (the mean absolute errors are lower than 0.5 LU). Furthermore, this technique has been used for prediction of water solubility for an expanded set of twenty three nitro compounds including nitroaromatic, nitramines, nitroanisoles, nitrogen rich compounds and some their nitroso and amino derivatives with unknown experimental values. The solubility values predicted using the proposed computational technique could be useful for the determination of the environmental fate of military and industrial wastes and the development of remediation strategies for contaminated soils and waters. This predictive capability is especially important for unstable compounds and for compounds that have yet to be synthesized.
Finally, an application of COSMO-RS approximation to the prediction of other environmentally important physical properties is briefly discussed.