Mechanistic Insight into the Molecular TiO₂-Mediated Gas Phase Detoxication of DMMP: A Theoretical Approach

Abstract

The detoxication of DMMP (dimethyl methylphosphonate) mediated by molecular TiO has been investigated computationally using density functional theory (DFT). From our previous studies, it is evident that the unimolecular detoxication of OPCs (organophosphorus compounds) is kinetically unfeasible at room temperature due to the significantly high activation barrier. Thus, the aim of our work is to find out whether molecular TiO can make any significant impact on the kinetic feasibility of the detoxication processes or not. Here, we have identified a total of three detoxication pathways, where in the first step the detoxication occurs through H-abstraction with the assistance of TiO, and in the second step, the titanium complex is separated from the respective phospho-titanium complexes. The outcomes reveal that the TiO-mediated detoxication pathways are at least 20.0 kcal/mol more favorable than their respective unimolecular pathways and that among them, the α-H-mediated isomerization is found to be the most feasible pathway. When the separation of a titanium complex is under consideration, the double HO-assisted mechanism is found to be the favored pathway. Overall, the entire work provides a widespread idea about the efficiency of molecular TiO-assisted detoxication of DMMP, which can be well applicable to other OPCs also.

A Theoretical and Mass Spectrometry Study of Dimethyl Methylphosphonate: New Isomers and Cation Decay Channels in an Intense Femtosecond Laser Field

“…These conformers lie within the 1.9 kcal/mol total energy range. The MA geometrical topology was assumed in computations of the DMMP absorption on the TiO 2 anatase (001) and (110) , surfaces, in a study of TiO 2 -mediated gas-phase detoxification of DMMP, in simulations of DMMP adsorption and reactivity on amorphous silica surfaces and when interpreting the data obtained using two electron spectroscopy methods . In this work, we explored if the MA CH 3 PO­(OCH 3 ) 2 topology corresponds to the geometrical structure of the ground states of dimethyl methylphosphonate and performed an extensive search using different ligand compositions around the phosphorus atom.…”

Titania Nanomaterials for Sarin Decomposition: Understanding Fundamentals

“…The great diversity of metal oxides and their abundant surface chemistry suggest an appealing opportunity and vast potential to find suitable filter materials among metal oxides. ,, In the past decades, a wide range of metal oxides have been explored for the application of GB (its simulant DMMP as well) adsorption and decomposition. ,,,,− TiO 2 is among the most studied metal oxides in this application ,,− ,− because of its wide popularity in other applications , as well as its high tunability in the atomic and nanoscale . Recent impressive advances in nanosynthesis and characterization lead to the attempt to probe TiO 2 nanomaterials for GB or DMMP decomposition.…”

Role of TiO2 Anatase Surface Morphology on Organophosphorus Interfacial Chemistry

“…This is consistent with previous gas-phase experimental and computational studies with strongest organophosphorus binding to Lewis acid (Ti) sites. [29][30][31][32][34][35][36]71,80,81 Other types of binding interactions, including hydrogen bonding between the surface and MP, ranging from −8.0 (for S•••H−O−Ti) to +13.3 kcal mol −1 (for five-coordinate Ti−O−P) can be considered (Supporting Information Figures S17 and S18) and may become important in aqueous solutions. We have used a polarizable solvent continuum model in all our DFT calculations, but we expect that binding energies and pK a values will be dependent on the number of surface water molecules.…”

“…Enhanced binding of environmental toxins can be due to increased surface areas of the adsorbent, surfaces having high defect densities with uncoordinated atoms, and the wide range of Lewis acid–base properties of these materials, with respect to atom composition and pH . Organophosphorus binding to metal oxides at room temperature occurs primarily through phosphoryl oxygen to Lewis acid metal sites, which are undercoordinated metal atoms inherent in the surface structure. − Adsorbate binding to TiO 2 will vary as a function of solution pH, electrolyte ionic strength, and organic pollutant speciation (uncharged or charged forms) . In turn, surface TiO 2 acid–base properties are determined by its crystallinity (long-range order), size (surface-to-volume ratios), aqueous electrolyte concentration, and surface morphology (i.e., exposed crystal planes).…”