A first principles investigation of aging processes in soman conjugated AChE.

We have examined the aging process of soman inhibited AChE using Density functional theory (DFT) calculations. The catalytic serine of AChE can be phosphonylated by the nerve agent soman, and subsequently can undergo an aging process. The consequences of irreversible inhibition of AChE due to the aging process is fatal for mammals. The DFT calculations shed light on some intricate features of aging process of soman inhibited AChE, which has been pondering in the literature. The DFT calculations (M05-2X/6-31G(∗) level of theory) performed with the model systems revealed that the dealkylation of pinacolyl group and the methyl migration takes place simultaneously. The role of pre-protonation and electrostatic stabilization by histidine (His440(+)) in catalyzing the aging process of soman inhibited AChE is energetically comparable. The aging process catalyzed by the histidine (His440(+)) residue reduces the free energy of activation by ∼14.0kcal/mol, which is in good agreement with the reported experimental results. Further, the calculated results reveal that tryptophan residue (Trp84) of the catalytic anionic subsite (CAS) assists the rearrangement reaction in the rearrangement process via cation-π interactions.