The encapsulation of organophosphorus (OP) nerve agents by pillar[5]arene (P5) molecule, shows that adsorption occurs with a larger structural reorganization of the host molecule. The computed binding energies shows that the complexes formed are more stable inside the cavity. Tabun was found to have the highest binding energy among the studied OPs. The computed Gibbs free energy is negative for Dimethyl methylphosphonate, sarin and tabun, and are positive for soman (GD) and ethyl-S-dimethylaminoethyl methylphosphonothiolate (VX). The inclusion complexes were found to have lower band gap. The quantum theory of Atoms-in-molecules analysis shows that ρ values were positive which implies the existence of noncovalent interactions. The Laplacian of the charge density ∇2ρ for bond critical points bonds are small and are negative which indicates the depletion of electronic charge along the bond paths and existence of an electrostatic nature of bonding between the guest and host molecule. The noncovalent interactions analysis clearly shows the existence of hydrogen bonding and van der Waals bonding in these inclusion complexes. The energy decomposition analysis shows that the, interaction between the P5 and the larger guest molecules VX and GD are mainly due to electrostatic interaction and for small guest, the interactions are mostly of van der Waals type.
Graphical Abstract