Hydrolysis of a VX-like Organophosphorus Compound through Dissociative Chemisorption on the MgO(001) Surface

Abstract

Organophosporous VX agent O-ethyl S-(2-diisopropylethylamino)ethyl methylphosphonothioate is one of the main nerve agents. For this reason, the search for ways to deactivate it is very important. In this work, hydrolysis and adsorption reactions of a VX-like compound (O,S-dimethyl methylphosphonothioate, DMPT) on the MgO(001) surface were studied by density-functional theory (DFT) using periodic boundary conditions. A degradation reaction mechanism was proposed and theoretically investigated on two types of MgO(001) surfaces: the terrace and the Al-doped. Conformations, free-energy differences, transition states, reaction barriers, and minimum-energy paths were computed. We found that the P–S bond, related to the agent toxicity, breaks via hydrolysis occurring spontaneously throughout the analyzed temperature range, 100–600 K. In the dissociative chemisorption of the DMPT molecule, the formation of the MgO:[PO(CH3)(OCH3)]+[SCH3]− intermediate is catalytically favored from a temperature of about 335 K for the Al-doped surface, a value considerable smaller than the 500 K value for the same process on the terrace. At 335 K, the dissociation fragments on the Al-doped surface are less stable in comparison to the hydrolysis products. The possible reconstitution of the P–S bond on both surfaces does not occur according to kinetic analysis; however, the electronic energy barrier for the direct dissociation reaction on the Al-doped sites is about 49.0 kJ/mol lower than the value for the terrace. After recombination with the OH– and H+ ions, the HOPO(CH3)(OCH3) and HSCH3 products do not accumulate on either surface because these molecules desorb below the DMPT dissociation temperatures. The Al-doped sites of MgO(001) are thus more active in the catalytic hydrolysis process of the VX-like organophosphorus compound than is the nondoped surface.

Molecular dynamics simulation of the electron ionization mass spectrum of tabun

“…An additional feature that encourages the analysis of simulated EI/MS is the possibility of determining the molecular structure of the formed fragments and the fragmentation pathways, which is usually not a trivial task employing static quantum‐chemical methods that determine potential energy minima and saddle points, as previously done regarding an alkaloid molecule 11 . Static density functional theory (DFT) combined with periodic‐boundary conditions can also be employed to investigate degradation mechanisms on the vicinity of a surface, as done on magnesium oxides surfaces in the case of sarin, 12 as well as to investigate the hydrolysis of a VX‐type compound 13 …”

Exploration of Unimolecular Gas-Phase Detoxication Pathways of Sarin and Soman: A Computational Study from the Perspective of Reaction Energetics and Kinetics

“…Recent years have witnessed a sharp increase of concern about the organophosphorus compounds − (OPCs), one of the most nefarious synthetic chemical derivatives. The use of OPCs as agricultural chemicals such as insecticides, pesticides, herbicides, etc.…”

“…OPCs can be decomposed through different processes such as hydrolysis, , thermal decomposition, , combustion, catalytic decomposition, and so forth. Degradation of OPCs using solid surfaces such as Brucite, MgO(001), TiO 2 , − SiO 2 , Rh(100), Mo(111), Pt(111), Ni(111), Pd(111), Al 2 O 3 , − Fe 2 O 3 , Y 2 O 3 , and aluminum-supported iron oxide are also performed. In the year 1962, Gustafson et al kinetically studied the decomposition of O-isopropyl methylphosphonofluoridate (sarin) through hydrolysis using copper­(II) chelates of diamine as catalysts.…”

“…The base-catalyzed hydrolysis of 1,2,2-trimethylpropyl methylphosphonofluoridate (soman) was studied by Ward et al, 5 where the nucleophilic substitution of F − by OH − reveals the way of deactivation of acetylcholinesterase enzyme. Alvim et al 12 investigated the hydrolysis of VX-like OPCs (O,S-dimethyl methylphosphonothioate, DMPT) on two types of MgO(001) surfaces, namely, the terrace and the Al-doped surfaces through dissociative chemisorptions using density functional theory (DFT). Templeton et al 25 examined the adsorption and decomposition of diisopropyl methylphosphonate (DIMP), DMMP, and diphenyl methylphosphonate (DPMP) on an aluminum oxide surface via tunneling spectroscopy.…”

“…Figures 10,11,12,and 13), it is evident that at a lower temperature range the k T of the D3 pathway is the highest among all but that with the increase of temperature (>700 K) the isomerization pathways are found to be more or less equally kinetically feasible like the D3 pathway. The kinetic feasibility of the detoxication pathways can also be well justified by determining the branching ratio (b.r.)…”