Physicochemical Properties of Hazardous Energetic Compounds from Molecular Simulation

A protocol is presented and used for the computation of physicochemical properties of nitroaromatic energetic compounds (ECs) using molecular simulation. Solvation and self-solvation free energies of ECs are computed using an expanded ensemble (EE) molecular dynamics method, with the TraPPE-UA/CHELPG and CGenFF/CHELPG force field models. Thermodynamic pathways relating Gibbs free energies and physicochemical properties are used to predict the room temperature vapor pressures, solubilities (in water and 1-octanol), Henry's law constants, and partition coefficients (octanol-water, air-water, and air-octanol) for liquid, subcooled, and solid ECs from the molecular simulations. These predictions are compared to experimental data where available. It is found that the use of the TraPPE-UA model with CHELPG charges computed here leads to predictions of measured physicochemical properties of comparable accuracy to that of other theoretical and empirical models. However, the advantage of the method used here is that with no experimental data, unlike other methods, a number of physicochemical properties for a compound can be calculated from only its atomic connectivity, charges obtained from density function theory (DFT), and choice of force field using two simulations: its self-solvation free energy and its Gibbs free energy in a solvent.