Elucidating the degradation mechanism of the nerve agent A-234 using various detergents: a theoretical investigation

Abstract

A-234 (ethyl N-[1-(diethylamino)ethylidene]phosphoramidofluoridate) is one of the highly toxic Novichok nerve agents, and its efficient degradation is of significant importance. The possible degradation mechanisms of A-234 by H₂O, H₂O₂, NH₃, and their combinations have been extensively investigated by using density functional theory (DFT) calculations. According to the initial intermolecular interaction and the proton transfer patterns between the detergent and the substrate A-234, the A-234 degradation reaction is classified into three categories, denoted as A, B, and C. In modes A and B, the degradation of A-234 by H₂O₂, H₂O, and NH₃ is initiated by the nucleophilic attack of the O or N atom of the detergent on the P atom of A-234, coupled with the proton transfer from the detergent to the O or N atom of A-234, whereas in mode C, the direct interaction of H₂N–H with the F–P bond of A-234 triggers ammonolysis through a one-step mechanism with the formation of H–F and N–P bonds. Perhydrolysis and hydrolysis of A-234 can be remarkably promoted by introducing the auxiliary NH₃, and the timely formed hydrogen bond network among detergent, auxiliary, and substrate molecules is responsible for the enhancement of degradation efficiency.