A molecular simulation-based thermodynamic protocol has been developed to predict a wide variety of physicochemical properties of environmental contaminants. Vapor pressure of a contaminant is computed from its self-solvation free energy either at liquid phase or at subcooled state (for a solid contaminant at a given temperature). Solubility, Henry's law constant, activity coefficient, and air-solvent partition coefficient of a contaminant in a solvent are calculated from the combination of solvation and its self-solvation free energies. Any solvent-solvent partition coefficient can be also calculated from the solvation free energies of the contaminant in two solvents. These physicochemical properties are also predicted as functions of temperatures for which experimental data are scarce. In principle, this protocol can be applied to any solvent-solute pair at any temperature.  We have demonstrated the capability of the method using a set of hazardous explosive compounds and three solvents: water, 1-octanol, and hexane. The expanded ensemble molecular dynamics method is used to compute Gibbs solvation free energies. Both explosives and solvents are modeled using transferable force fields with the partial atomic charges obtained from density function theory calculations. The success of the method is verified by demonstrating a reasonable with the scattered experimental data that are available. For example, the reliability of the method has been examined by predicting most important partition coefficients with average unsigned error of less than 0.5 log units.  An important feature of this method is that it is completely predictive, does not rely on any experimental data, and uses only the atomic connectivity. Therefore, the method can be used for any molecule, including those not yet synthesized. So it has value for predicting thermophysical properties of materials for which experimental measurement is difficult and predicting the likely environmental impact of new chemicals, energetic materials or other hazardous compounds.

Molecular simulation-based thermodynamic protocol for computing physicochemical properties of environmental contaminants

246th National Meeting (2013)

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