Sarin Decomposition Research Articles

Diisopropyl Methylphosphonate and Sarin Decomposition on Pristine vs Hydroxylated Alumina Surfaces: Mechanistic Predictions from Ab Initio Molecular Dynamics

Diisopropyl Methylphosphonate and Sarin Decomposition on Pristine vs Hydroxylated Alumina Surfaces: Mechanistic Predictions from Ab Initio Molecular Dynamics

Experimental Study of the Adsorption and Decomposition of Sarin on Dry Copper(II) Oxide.

Organophosphonates were originally developed as insecticides but were quickly identified as highly toxic acetylcholinesterase inhibitors, leading to their exploitation as chemical warfare agents (CWA). To develop next generation filtration technologies, there must be a fundamental understanding of the molecular interactions occurring with toxic chemicals, such as CWAs. In this paper, we investigate the interaction between dry CuO nanoparticles and sarin (GB), using infrared (IR) spectroscopy in an effort to build an atomic understanding. We show sarin strongly interacts with CuO and then quickly degrades, primarily through the cleavage of the P-F bond, creating a bridging species on the CuO surface with the assistance of lattice oxygen. Upon heating, the decomposition product isopropyl methyl phosphonic acid (IMPA) does not continue to decompose but desorbs from the surface. These observations are further elaborated through theoretical models of sarin on dry CuO (111).

Decomposition for Chemical Warfare Agent Sarin: Comparation Between Plate-to-Plate and Plate-to-Pin Dielectric Barrier Discharge

The degradation of chemical warfare agent (CWA) sarin using plate-to-plate and plate-to-pin electrode structure dielectric barrier discharges (DBDs) was studied in this work. The discharge characteristics, optical emission, decomposition efficiency, and decomposition products in the above apparatus were well investigated. With initial pure sarin of <inline-formula> <tex-math notation="LaTeX">$20 ~\mu \text{L}$ </tex-math></inline-formula>, the decomposition amount per unit time and decomposition efficiency were obtained to be <inline-formula> <tex-math notation="LaTeX">$14.68 \times 10^{-3}$ </tex-math></inline-formula> mg/s and <inline-formula> <tex-math notation="LaTeX">$0.25 ~\mu \text{g}$ </tex-math></inline-formula>/J, for plate-to-plate DBD, and <inline-formula> <tex-math notation="LaTeX">$9.16 \times 10^{-3}$ </tex-math></inline-formula> mg/s and <inline-formula> <tex-math notation="LaTeX">$0.167 ~\mu \text{g}$ </tex-math></inline-formula>/J, for plate-to-pin DBD, respectively. The decomposition products containing isopropyl methylphosphoric acid (IMPA), methylphosphoric acid (MPA), fluoro(methyl)phosphinic acid (MPFA), di-isopropyl methane phosphate (DIMP), and phosphoric acid (PA) were observed in both DBD devices, with MPA and PA as the final products. The production level of PA was highest among all the products in plate-to-plate DBD. However, in plate-to-pin DBD, the concentration of PA and MPA were at the same level. The different decomposition efficiency between two DBD devices were mainly ascribed to the different input energy and their configuration. Our results confirmed that plate-to-plate DBD was a high-efficiency decomposition technology for sarin decomposition.

High-Temperature Decomposition of Diisopropyl Methylphosphonate on Alumina: Mechanistic Predictions from Ab Initio Molecular Dynamics

The enhanced degradation of organophosphorous-based chemical warfare agents (CWAs) on metal-oxide surfaces holds immense promise for neutralization efforts; however, the underlying mechanisms in this process remain poorly understood. We utilize large-scale quantum calculations for the first time to probe the high-temperature degradation of diisopropyl methylphosphonate (DIMP), a nerve agent simulant. Our Born-Oppenheimer molecular dynamics (BOMD) calculations show that the $\gamma$-Al$_2$O$_3$ surface shows immense promise for quickly adsorbing and destroying CWAs. We find that the alumina surface quickly adsorbs DIMP at all temperatures, and subsequent decomposition of DIMP proceeds via a propene elimination. Our BOMD calculations are complemented with metadynamics simulations to produce free energy paths, which show that the activation barrier decreases with temperature and DIMP readily decomposes on $\gamma$-Al$_2$O$_3$. Our first-principle BOMD and metadynamics simulations provide crucial diagnostics for sarin decomposition models and mechanistic information for examining CWA decomposition reactions on other candidate metal oxide surfaces.

Degradation of Fatal Toxic Nerve Agents on Dry TiO2.

Despite a recent dramatically increased risk of using chemical warfare agents in chemical attacks and assassinations, fundamental interactions of toxic chemicals with other materials are poorly understood, and micromechanisms of their chemical degradation are yet to be established. This represents an outstanding challenge in both fundamental science and practical applications in combat against chemical weapons. One of the most versatile and multifunctional oxides, TiO2, has been suggested as a promising material to quickly adsorb and effectively destroy toxins. In this paper, we explore how sarin (also known as GB) adsorbs and decomposes on dry nanoparticles of TiO2 anatase and rutile phases. We found that both anatase and rutile readily adsorb sarin gas molecules because of a strong electrostatic attraction between the phosphoryl oxygen and surface titanium atoms. The sarin decomposition most likely proceeds via a propene elimination; however, the reaction is exothermic on the rutile (110) surface and endothermic on the anatase (101) surface. High energy barriers suggest that sarin would hardly decompose on pristine dry surfaces of TiO2, and degradation reactions can be triggered by defects or contaminants under realistic operational conditions.

The decisive role of pericyclic reactions in the thermal decomposition of organophosphorus compounds

The understanding of the thermal decomposition chemistry of chemical warfare nerve agents is largely limited by the scarcity of kinetic data. Because of the high toxicity of these molecules, experimental determination of their chemical properties is very difficult. In the present work, a comprehensive detailed kinetic model for the decomposition of sarin and some simulants, i.e. di-isopropyl methyl phosphonate (DIMP), diethyl methylphosphonate (DEMP), and triethyl phosphate (TEP) were developed, containing possible molecular and radical pathways. The importance of unimolecular pericyclic decomposition led to evaluate precisely the rate constants of these reactions with high level theoretical calculations. The QCISD(T)/cc-PV∞QZ//B2PLYPD3/6–311+G(2d,d,p) level of theory was selected after a benchmark. The contribution of hindered rotors was included with the 1D-HR-U approach. Tunneling was taken into account for H-atom transfer. Transition state theory was used to calculate high-pressure limit rate constants and pressure dependent rate constants were calculated using Master Equation modeling. The model was validated against experimental pyrolysis and oxidation experimental data available in literature. Flux analyses showed that whatever the conditions are, the first step of decomposition of the studied phosphorus compounds are pericyclic eliminations leading to successive decompositions, whereas bond-breaking or H-atom abstraction remain negligible, even at high temperature.

Mechanisms of Degradation of Toxic Nerve Agents: Quantum-chemical Insight into Interactions of Sarin and Soman with Molybdenum Dioxide

With the urgent need to provide an efficient and reliable protection for people from fatal chemical and biological weapons, our fundamental understanding of how toxins interact with filters is far from complete. The situation is further complicated by natural difficulties of performing experimental measurements with lethal toxins. Unlike experiments, computational modeling offers an attractive and safe yet reliable way of studying behavior of toxic agents on a variety of substrates at a great level of detail. Here, we report DFT-based quantum-chemical calculations of adsorption and decomposition of DMMP, sarin and soman on MoO2 (011) surface. Our calculations show that MoO2 strongly adsorbs toxic nerve agents and quickly decomposes them.Decomposition of DMMP on the MoO2 (011) surface proceeds via the PO-CH3 bond breaking and a formation of a surface methoxy group. The calculated activation barrier for this reaction is 131.5 kJ mol−1. Unlike DMMP, decomposition of sarin and soman proceeds via the dealkylation reaction yielding propene and 3,3-dimethyl-1-butene, respectively. Decomposition of sarin requires a remarkably low energy (53.7 kJ mol−1), whereas the similar reaction in soman requires 50 kJ mol−1 more energy. We also make specific predictions to guide Ambient-Pressure X-ray Photoelectron Spectroscopy (APXPS) experiments on sarin interaction with MoO2 samples. We conclude that MoO2 serves as an efficient substrate able of degrading toxins.

Development of a High-Efficiency Decomposition Technology for Volatile Chemical Warfare Agent Sarin Using Dielectric Barrier Discharge

High-efficiency decomposition technology for volatile chemical warfare agent sarin was developed using a dielectric-barrier discharge (DBD). The power consumptions of the developed device for which the gap lengths of the plasma-generation sites were 1.0–2.0 mm, were found to be 22–27 W, respectively. The DBD driven sarin-decomposition amount per unit time and the decomposition efficiency in the optimized condition were obtained to be 2.05 × 10−3 mg/s and 1.38 × 10−4 mg/W, respectively, measured by ion mobility spectrometer. Sarin-decomposition products were investigated using a gas chromatography–mass spectrometry with tert-butyldimethylsilylation derivatization, indicating that isopropyl methylphosphoric acid (IMPA), methylphosphoric acid (MPA), and phosphoric acid (PA) were generated during sarin decomposition by DBD. The decomposition efficiency at 37 W decreased by 41% molar concentration compared with that at 15 W, but the production levels of IMPA, MPA and PA were changed from 10.0%, 41.5% and 3.9% to 7.2%, 21.3% and 6.4%, respectively.

Sarin Decomposition on Pristine and Hydroxylated ZnO: Quantum-Chemical Modeling

An atomistic understanding of interactions between chemical warfare agents (CWAs) and filter materials is crucial for discovery and design of new materials suitable for chemical protection. The high toxicity of CWAs is a major barrier for experimental studies and significantly impedes the development of improved filter materials. Our recent studies show that density functional theory-based modeling serves as a powerful companion to experimental studies and assists in interpretation of experiments performed on surface-enhanced degradation of CWA simulant compounds. A strong synergy between theory and experiment enables predictive modeling of interactions of toxic CWAs with filter materials. Here, we present a comprehensive study of sarin adsorption and decomposition on pristine and hydroxylated ZnO(1010) surfaces performed by means of quantum-chemical calculations. We found that both simulated ZnO surfaces (an idealized pristine surface and hydroxylated surface, a more realistic and relevant form of ZnO a...

Computational Screening of Roles of Defects and Metal Substitution on Reactivity of Different Single- vs Double-Node Metal–Organic Frameworks for Sarin Decomposition

Understanding how different factors affect the electronic properties of metal–organic frameworks (MOFs) is critical to understanding their potential for catalysis and to serve as catalyst supports. In this work, periodic dispersion-corrected quantum mechanical calculations are performed to assess the catalytic activity of different Zr6 vs Zr12 MOFs for the heterogeneous catalytic hydrolysis of the chemical warfare agent sarin. Using a comprehensive series of extended periodic models capable of capturing long-range sarin/water/framework interactions in both Zr6 and Zr12 MOFs, the effects of numbers and morphologies of defective sites, as well as ZrIV substitution with heavier CeIV, are thoroughly investigated. Our calculations show that hydrogen bonds involving both metal-oxide nodes and organic linkers can play important roles in the catalysis. Insights derived from this work should inform the design and realization of more effective and robust next-generation MOF-based heterogeneous catalysts.

Engineering Bacteria to Catabolize the Carbonaceous Component of Sarin: Teaching E. coli to Eat Isopropanol.

We report an engineered strain of Escherichia coli that catabolizes the carbonaceous component of the extremely toxic chemical warfare agent sarin. Enzymatic decomposition of sarin generates isopropanol waste that, with this engineered strain, is then transformed into acetyl-CoA by enzymatic conversion with a key reaction performed by the acetone carboxylase complex (ACX). We engineered the heterologous expression of the ACX complex from Xanthobacter autotrophicus PY2 to match the naturally occurring subunit stoichiometry and purified the recombinant complex from E. coli for biochemical analysis. Incorporating this ACX complex and enzymes from diverse organisms, we introduced an isopropanol degradation pathway in E. coli, optimized induction conditions, and decoupled enzyme expression to probe pathway bottlenecks. Our engineered E. coli consumed 65% of isopropanol compared to no-cell controls and was able to grow on isopropanol as a sole carbon source. In the process, reconstitution of this large ACX complex (370 kDa) in a system naïve to its structural and mechanistic requirements allowed us to study this otherwise cryptic enzyme in more detail than would have been possible in the less genetically tractable native Xanthobacter system.

Adsorption of sarin on MgO nanotubes: Role of doped and defect sites

Sarin is a highly toxic organophosphorus chemical warfare agent which has been employed in various wars and terrorist attacks. Due to an urgent need of finding safe methods to decompose this toxic nerve agent, the research on decomposition of sarin gains importance. In the present work, the decomposition of sarin molecule on MgO nanotube and Ti-doped MgO nanotube has been investigated. For this purpose, the structural and electronic characteristics of nanotubes are first examined. It is seen that although doping with Ti modifies the properties of the nanotube, adsorption of sarin on both kinds of nanotubes presents similar characteristics. Adsorption is found to be more favorable at low-coordinated sites, i.e., the 3c site is preferred over 4c. Five kinds of surface defect sites have been considered i.e., O4c, O4c2−, Mg4c, Mg4c2+ and (MgO)4c. Adsorption of sarin on various defect sites produces different products. In two of the cases, the neutral oxygen defect and MgO defect, the molecule breaks completely into fragments and is destructively decomposed. Hence, our study proposes a new metal oxide system that might destructively adsorb chemical warfare agents and highlights the need for further exploration of untested metal oxide systems.

UV-assisted photocatalytic synthesis of TiO2-reduced graphene oxide with enhanced photocatalytic activity in decomposition of sarin in gas phase

TiO2-reduced graphene oxide (RGO) composite are successfully prepared by UV-assisted photocatalytic reduction of graphite oxide by TiO2 nanoparticles in ethanol. These nanocomposites prepared with different ratios of graphene oxide (GO) were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction spectroscopy, UV–vis absorption spectrophotometer (UV–vis), and X-ray photoelectron spectroscopy. Photocatalytic degradation of nerve agent, isopropyl methylphosphonfluroride, Sarin (GB) as a real Chemical Warfare Agent on nanocomposites have been studied using Gas chromatography/mass spectrometry analysis in ambient atmosphere. RGO-TiO2 nanocomposites exhibited much higher photocatalytic activity than TiO2 for degradation of GB under visible light irradiation.

Determination of the Surface Effects on Sarin Degradation

While it is well established that the dominant degradation mechanism for the chemical warfare agent, sarin, is hydrolysis via an SN2 mechanism in aqueous environments, the same cannot be said when hydrophilic or hydrophobic surfaces are present. Utilizing first-principles molecular dynamics simulations based on density functional theory, potential degradation pathways for sarin were investigated in the vicinity of both hydrophilic and hydrophobic surfaces. In an idealized situation where sarin is within hydrogen-bonding distance to a hydrophilic surface, the most probable degradation occurred via an SN2 mechanism, but with a lowering of the reaction barrier (ΔΔG⧧) of ∼15 kcal/mol as compared with bulk aqueous SN2 decomposition. However, in the presence of an idealized hydrophobic surface, it was found that the degradation mechanism for sarin proceeded via an SN1-type mechanism where the phosphorus–fluorine bond breaks first, followed by a second step in which water acts as a nucleophile. The reaction barrier associated with such a reaction is ∼10 kcal/mol higher than the SN2 degradation path found in bulk aqueous environments. The results found here clearly demonstrate how surfaces can significantly alter sarin decomposition.

Decomposition of phosphonofluoridates on glass

Neat droplets of O,O-diisopropylphosphorofluoridate (DFP) and O-1,2,2-trimethylpropyl methylphosphonofluoridate (Soman) decompose on glass. In thirty hours at room temperature over 40% of the Soman has been decomposed while nearly 15% of the DFP has been degraded. NMR spectroscopic analysis of the Soman showed that Soman decomposed exclusively by scission of the PF bond to form O-1,2,2-trimethylpropyl methylphosphonic acid. The rate of decomposition of the two organophosphorus fluorine substrates is proportional to the rate of hydrolysis. The results are consistent with earlier studies which showed that silica or magnesia promoted the decomposition of sarin (O-2-propylisopropyl methylphosphonofluoridate). The rate of decomposition on glass is accelerated in the presence of high humidity.

Ion exchange resins as catalysts in the decomposition of sarin

AbstractThe hydrolysis rate of the nerve gas Sarin in aqueous solution may be accelerated by strongly acidic and strongly basic ion exchange resins. Basic resins are more effective than acid resins. Depending on the resin type and internal structure, a diffusional process or the chemical reaction may be rate determining. In distilled water, cationic resins behave as true catalysts, whereas the products of decomposition of Sarin destroy the effectiveness of anion resins. Dissolved salts in the water lower the useful life of both types of resins by replacement of the active hydrogen or hydroxyl groups.