Comprehensive global energy minimum modeling of the sarin-serine adduct

DFT-based molecular dynamics and quantum chemistry theory approaches are combined to investigate the various conformers of sarin-serine adduct. Twenty different conformers have been located as the local minima on the potential energy surface. They are categorized into five classes based on the relative orientation of sarin moiety. The energy properties of the twenty sarin-serine conformers revealed in the present study suggest that at least four of the conformers (1-1, 4-1, 4-2, and 5-1) are expected to have crucial contributions to the phosphonylation and dealkylation reactions of the sarin-serine adduct at low temperature. Among them, the 1-1 conformer which has both the lowest energy and the highest Boltzman distribution relative probability is expected to be the most important. However, as the temperature rises, the 4-1 conformer plays a more important role than 1-1 in the sarin-serine adductation reactions. Under the relatively high temperatures, the contribution of conformer 5-1 decreases in the phosphonylation and dealkylation reactions while at least eight other conformers (1-2, 1-3, 3-1, 3-4, 3-7, 4-2, 4-3, and 4-4) are expected to have larger contributions in these reactions.