Prediction of 1-octanol-water and air-water partition coefficients for nitro-aromatic compounds from molecular dynamics simulations.

United-atom force fields, based on the Transferable Potentials for Phase Equilibria (TraPPE), are developed for twelve nitro-aromatic compounds, which include 2,4-dinitrotoluene (2,4-DNT), 2,6-dinitrotoluene (2,6-DNT), 3-nitrotoluene (3-NT), 4-nitrotoluene (4-NT), 1,3-dinitrobenzene (1,3-DNB), 1,4-dinitrobenzene (1,4-DNB), 2,4-dinitroanisole (DNAN), 1,3,5-trinitrobenzene (TNB), 2,4,6-trinitrotoluene (TNT), 2-nitroanisole (2-NAN), 4-nitroanisole (4-NAN) and n-methyl-p-nitroaniline (MNA). 1-Octanol-water and air-water partition coefficients are predicted for the optimized TraPPE-UA force field with adaptive biasing force molecular dynamics simulations, and compared to available experimental data. Log Kow values are predicted with an average absolute deviation of 0.2 log units, while Henry's law constants are predicted to with an average absolute deviation of 0.5 log units. Two additional models are presented for energetic materials with five membered rings for which no experimental data are available in the open literature: 3,5-dinitropyrazole (DNP) and 3-nitro-1,2,4-triazole-5-one (NTO). Investigation of the local microstructure around each solute reveals that 1-octanol is able to form hydrogen bonded chains around the solute, while little organized microstructure was observed around the solutes in water.