Catalytic methods for the destruction of chemical warfare agents under ambient conditions

This tutorial review--which should particularly appeal to chemists, biochemists, and molecular biologists interested in catalysis, redox processes, and enzymology--summarizes the recent progress toward developing catalysts capable of destroying one or more of the classical chemical warfare agents under ambient conditions. Specifically, we explore the reactions of sulfur mustard, the G-series of organophosphorus nerve agents including sarin and soman, and the organophosphorus nerve agent, VX. Catalysts range from metal-centered oxidation catalysts to engineered catalytic antibodies.     

Synthesis and anticholinesterase activity of some new fluorogenic analogues of organophosphorus nerve agents

Eighteen new fluorogenic analogues of organophosphorus nerve agents were synthesised and characterised. They included analogues of tabun, sarin, cyclosarin, soman, VX, and Russian VX, with the 7-oxy-4-methylcoumarin or 7-oxy-4-(trifluoromethyl)coumarin leaving group. These analogues inhibited acetylcholinesterase (AChE) effectively in vitro and therefore have potential as tools for the identification of novel organophosphatases in biological systems. Analogues of VX and Russian VX with the 7-amino-4-methylcoumarin group, although poor AChE inhibitors, may have utility for screening enzyme libraries for phosphoramidases capable of cleaving P-N bonds.     

Sarin and Soman: Structure and Properties

The most stable conformers of sarin (isopropyl methylphosphonoflouridate) and soman (pinacolyl methylphosphonofluoridate) are determined in high-level-correlated calculations with extended Gaussian basis sets. The two molecules are found to have three low-energy conformers each. For both molecules two of the lowest energy conformers have almost the same energies with a very small barrier separating the corresponding minima. The third conformer of sarin is found to lie about 1 kcal/mol above the lowest energy form. For soman the corresponding value is equal to about 4 kcal/mol. The significance of these data for the mechanism of the toxic action of sarin and soman is discussed. According to our investigations sarin and soman are highly similar electronically and differences in their features arise mostly from the size and spatial arrangement of the alkoxy substituent at phosphorus. Also the influence of solvents on the conformations and solvation energies of sarin and soman is investigated.     

Nerve Agents Assay Using Cholinesterase Based Biosensor

Electrochemical biosensor based on electric eel acetylcholinesterase (AChE) (EC 3.1.1.7) was performed for assay of nerve agents – tabun, sarin, soman, cyclosarin, and VX. The biosensor used AChE as biorecognition element. The presence of nerve agents was accompanied by a strong inhibition of AChE activity. Enzyme activity is easily measurable by electrochemical oxidation of thiocholine created from acetylthiocholine (ATChCl) by AChE‐catalyzed hydrolysis. The tested nerve agents were successfully assayed. The best limits of detection were achieved for sarin (5.88×10^?10 M) and VX (8.51×10^?10 M) after one‐minute assay. The biosensor was found long term stable at low as well as laboratory temperature.     

Identification of Pairs of Organophosphorus Warfare Agents through Cholinesterase Reaction

Construction of Detehit (nerve-agent detector), a colorimetric biosensor of nerve agents, enables its utilization for selective analysis of nerve agents based on the different ability of nucleophilic reagents to reactivate enzyme-inhibitor complexes in the phase before dealkylation. For this purpose mono- and bispyridinium aldoximes, common in treatment of nerve agent poisoning, are used.

For a positive identification of a pair of organophosphates, a neural network analysis was used. The analysis was processed based on spectral data of the intensity of color changes of the surface of a cotton cloth reaction zone with immobilized and stabilized enzyme acetylcholinesterase. Color changes are based on Ellman's reaction. Intensity of these changes depends on activity of the enzyme after inhibition and reactivation of enzyme-inhibitor complex. The following nerve agents were identified: sarin, soman, tabun, cyclosarin, VX, and R-33.     

Determination of sarin, soman and their hydrolysis products in soil by packed capillary liquid chromatography-electrospray mass spectrometry

An analytical method based on aqueous ultrasonic extraction and packed capillary liquid chromatography-electrospray mass spectrometry (LC-ESI-MS) analysis was developed and compared to an existing gas chromatography(GC)-MS based method for the determination of sarin, soman and their hydrolysis products in contaminated soil. Three soils, a red clay, a tan sandy clay and a brown sandy clay loam, were spiked with sarin and soman and their initial hydrolysis products, isopropyl methylphosphonic acid and pinacolyl methylphosphonic acid, at the 10 microg/g level to assess recovery efficiency. Recovery of sarin and soman from the aqueous soil extracts was comparable to the existing analytical method, with a significant improvement in recovery being demonstrated for the chemical warfare agent hydrolysis products. Sarin and soman were recovered in the 20-90% range from the three soil types with aqueous extraction, while the hydrolysis products of these chemical warfare agents were extracted with recoveries in excess of 80%. The developed soil extraction and analysis method appears to be an attractive alternative to the GC-MS based method, since aqueous extracts containing chemical warfare agent hydrolysis products may be analysed directly, eliminating the need for additional sample handling and derivatization steps.     

Determination of Toxic Organophosphorus Compounds by Specific and Nonspecific Detectors

Abstract

Sample preparation procedures and gas chromatography methodology are presented for the determination of tabun, sarin, soman, and VX in aqueous solutions. Extraction recoveries from chloroform were quantitative. Peak area ratios of organophosphorus compounds (OPs) to internal standard versus concentrations of OP were linear over the range of 10-1000 (μg/ml when determined by the flame ionization detector and 10-800 μg/ml when determined by the flame photometric detector. Imprecision occurring at low ng concentrations of VX was caused by its adsorption on the analytical column. Acceptable precision was regained by the addition of a weak base, such as atropine, to the sample extract prior to its injection onto the gas chromatograph (GC).     

Gas-Chromatographic Determination of Sarin, Soman, and O-Isobutyl S-2-(N,N-Diethylamino)ethyl Methylphosphonothioate (a VX-Like Compound) Traces in Water

A gas-chromatographic procedure for the determination of O-isobutyl S-2-(N,N-diethylamino)ethyl methylphosphonothioate (VX), sarin, and soman in water at levels of 2 × 10^–6, 5 × 10^–5, and 2 × 10^–6 mg/L, respectively, was proposed. The procedure includes liquid–liquid extraction with the use of salting-out agents, back extraction, and evaporation. In this case, the VX compound was converted into O-isobutyl O-methyl methylphosphonate (a substance convenient for chromatographic determination) by the reaction with hydrochloric acid, methanol, thriethylamine, and silver nitrate.     

Selective enrichment of the degradation products of organophosphorus nerve agents by zirconia based solid-phase extraction

Selective extraction and enrichment of nerve agent degradation products has been achieved using zirconia based commercial solid-phase extraction cartridges. Target analytes were O-alkyl alkylphosphonic acids and alkylphosphonic acids, the environmental markers of nerve agents such as sarin, soman and VX. Critical extraction parameters such as modifier concentration, nature and volume of washing and eluting solvents were investigated. Amongst other anionic compounds, selectivity in extraction was observed for organophosphorus compounds. Recoveries of analytes were determined by GC-MS which ranged from 80% to 115%. Comparison of zirconia based solid-phase extraction method with anion-exchange solid-phase extraction revealed its selectivity towards phosphonic acids. The limits of detection (LOD) and limit of quantification (LOQ) with selected analytes were achieved down to 4.3 and 8.5 ng mL(-1), respectively, in selected ion monitoring mode.     

Synthesis and analysis of phosphorylated nonapeptide adducts by LC/Q-TOF MS

A new method for the synthesis of organophosphorylated adducts of the nonapeptide FGESAGAAS is presented. The adducts were obtained by using sarin (GB) or soman (GD) as the organophosphorylating reagents and cesium carbonate as the acid scavenger. Greater than 50% of the peptide was modified on serine 4. MS/MS spectra acquired on an Agilent 6520 quadrupole time of flight mass spectrometer demonstrated that serine 4, but not serine 9 in the nonapeptide, was modified. The adducts included the characteristic isopropyl group of sarin and the pinacolyl group of soman, indicating that aging had not occurred. It was concluded that the new synthetic method yielded sarin and soman-modified peptides that could be used as references when analyzing human exposure to these nerve agents.     

Gas-chromatographic determination of trace sarin and soman in atmospheric air of work zones and inhabited areas

A procedure was developed for the gas-chromatographic determination of sarin and soman in the atmospheric air of work zones and inhabited areas at a level of the maximum permissible concentration 2 × 10^?5 and 1 × 10^?5 mg/m³ and the tentative safe exposure level 2 × 10^?7 and 1 × 10^?7 mg/m³, respectively. The procedure is based on the recovery of sarin and soman from analyzed air using an absorbing solution, the extraction of sarin and soman from this solution with ethyl acetate and hexane, respectively, the evaporation of the corresponding extracts to a residual volume of 0.1 cm³, and their subsequent chromatography with flame-photometric and thermoionic detectors. The relative error in the determination of sarin and soman is 20 and 18 rel %, respectively, in the air of work zones and 27 and 23 rel %, respectively, in the air of inhabited areas.     

Gas Chromatographic–Mass Spectrometric Method for Quantitation of Trimethylsilyl Derivatives of Nerve Agent Degradation Products in Human Plasma, Using Strong Anion–Exchange Solid-Phase Extraction

For unequivocal proof of the use of nerve agents such as sarin, soman, cyclohexylsarin, VX, and Russian VX, a simple and accurate method, gas chromatography–mass spectrometry (GC–MS) after trimethylsilyl derivatization, was explored for simultaneous determination of the corresponding alkyl methylphosphonic acids (AMPAs) and of methylphosphonic acid (MPA) in human plasma. GC–MS analysis was performed after solid-phase extraction, with a strong anion-exchange cartridge, from plasma samples previously deproteinized with mercuric acetate, and then derivatization with bis(trimethylsilyl)trifluoroacetamide containing 5% trimethylchlorosilane. All five AMPA derivatives and the MPA derivative were separated to baseline within 11 minutes without interference. Linear calibration plots were obtained over concentrations ranging from 50 ng mL⁻¹ to 5 µg mL⁻¹. The relative standard deviation of recoveries ranged from 1.9 to 9.7% and detection limits were 22 ng mL⁻¹ or below.Revised: 3 and 23 May 2005     

Using Metal Complex Ion-Molecule Reactions in a Miniature Rectilinear Ion Trap Mass Spectrometer to Detect Chemical Warfare Agents

The gas-phase reactions of a series of coordinatively unsaturated [Ni(L)_n]^y+ complexes, where L is a nitrogen-containing ligand, with chemical warfare agent (CWA) simulants in a miniature rectilinear ion trap mass spectrometer were investigated as part of a new approach to detect CWAs. Results show that upon entering the vacuum system via a poly(dimethylsiloxane) (PDMS) membrane introduction, low concentrations of several CWA simulants, including dipropyl sulfide (simulant for mustard gas), acetonitrile (simulant for the nerve agent tabun), and diethyl phosphite (simulant for nerve agents sarin, soman, tabun, and VX), can react with metal complex ions generated by electrospray ionization (ESI), thereby providing a sensitive means of detecting these compounds. The [Ni(L)_n]²⁺ complexes are found to be particularly reactive with the simulants of mustard gas and tabun, allowing their detection at low parts-per-billion (ppb) levels. These detection limits are well below reported exposure limits for these CWAs, which indicates the applicability of this new approach, and are about two orders of magnitude lower than electron ionization detection limits on the same mass spectrometer. The use of coordinatively unsaturated metal complexes as reagent ions offers the possibility of further tuning the ion-molecule chemistry so that desired compounds can be detected selectively or at even lower concentrations.

Quantitation of five organophosphorus nerve agent metabolites in serum using hydrophilic interaction liquid chromatography and tandem mass spectrometry

Although nerve agent use is prohibited, concerns remain for human exposure to nerve agents during decommissioning, research, and warfare. Exposure can be detected through the analysis of hydrolysis products in urine as well as blood. An analytical method to detect exposure to five nerve agents, including VX, VR (Russian VX), GB (sarin), GD (soman), and GF (cyclosarin), through the analysis of the hydrolysis products, which are the primary metabolites, in serum has been developed and characterized. This method uses solid-phase extraction coupled with high-performance liquid chromatography for separation and isotopic dilution tandem mass spectrometry for detection. An uncommon buffer of ammonium fluoride was used to enhance ionization and improve sensitivity when coupled with hydrophilic interaction liquid chromatography resulting in detection limits from 0.3 to 0.5 ng/mL. The assessment of two quality control samples demonstrated high accuracy (101–105 %) and high precision (5–8 %) for the detection of these five nerve agent hydrolysis products in serum.     

Analysis of soman and sarin in blood utilizing a sensitive gas chromatography-mass spectrometry method

Gas chromatography with electron impact mass spectrometry and selected ion monitoring provided a simple and sensitive method for measuring organophosphorus compounds sarin and the two isomers of soman (isomer I and isomer II) in blood. These compounds were extracted from blood or isotonic saline using a modification of the method developed by Sass et al. Blood was deproteinized with perchloric acid before extraction. The acid-induced degradation of the organophosphorus compounds could be minimized by neutralizing the acid immediately after deproteinizing. In saline and blood, 81% of the extractable soman and 74% of the extractable sarin was recovered with a single extraction. The overall recovery of added organophosphorus was less in blood than in saline because of the binding of organophosphorus to blood constituents, probably various enzymes and proteins. A time-dependent decrease in extractable organophosphorus was found in whole blood but not in saline. Although soman isomer II was degraded in blood faster than soman isomer I, no significant difference in the affinities of these two isomers to acetylcholinesterase was observed.     

Ab initio molecular orbital and density functional studies on the solvolysis of sarin and O,S-dimethyl methylphosphonothiolate, a VX-like compound

[reaction: see text] Potential energy surfaces for the alkaline hydrolysis of sarin and O,S-dimethyl methylphosphonothiolate, a VX model compound, and the perhydrolysis of the latter have been computed at the MP2/6-31+G(d)//mPW1K/MIDI! level of theory. The effect of aqueous solvation was accounted for via the integral equation formalism polarizable continuum model (IEF-PCM) at the HF/6-31+G(d) level. Excellent agreement with the experimental enthalpy of activation for alkaline hydrolysis of sarin was found. For the alkaline hydrolysis of O,S-dimethyl methylphosphonothiolate, it was found that the P-O and P-S bond cleavage processes are kinetically competitive but that the products of P-S bond cleavage are thermodynamically favored. For the perhydrolysis of O,S-dimethyl methylphosphonothiolate, it was found that P-O bond cleavage is not kinetically competitive with P-S bond cleavage. In both cases, the data support initial formation of trigonal bipyramidal intermediates and demonstrate kinetic selectivity for nucleophilic attack on the face opposite the more apicophilic methoxide ligand.     

Cholinesterases in Biorecognition and Biosensors Construction: A Review

Acetylcholinesterase and butyrylcholinesterase are the only two known cholinesterases. Acetylcholinesterase plays an important part in cholinergic system. It terminates neurotransmission by hydrolysis of transmitter acetylcholine. The role of butyrylcholinesterase is not well understood. It is able to detoxify several compounds such as cocaine, succinylcholine, and so forth. The current review is focused on the application of cholinesterases in biorecognition. Cholinesterases are important markers in the body. Butyrylcholinesterase activity in plasma can serve as a liver function test or specific marker for sensitivity to myorelaxants or liver carcinoma. Both cholinesterases can serve as markers of poisoning by some neurotoxic compounds. Nerve agents (sarin, soman, tabun, VX), some Alzheimer disease drugs (galantamine, huperzine, donepezil, rivastigmine), pesticides (carbofuran, trichlorfon, paraoxon, malaoxon), and natural toxins (aflatoxin, pyridostigmine) can act as inhibitors of butyrylcholinesterase and/or acetylcholinesterase. Devices filled with immobilized cholinesterases can be used for the assay of the aforementioned toxins. In this review, methods for examination of cholinesterases activity in the body and in analytical devices are described. Applications, types of diagnosis, and assays are described as well.     

FT-IR analysis of chemical warfare agents

The qualitative and quantitative FT-IR analyses of dilute aqueous solutions of GA (tabun), GB (sarin), GD (soman), and VX were evaluated using the CIRCLE CELL^TM. Infrared spectra were recorded using a Nicolet 60SX FT-IR spectrometer fitted with a liquid nitrogencooled MCTA detector. The CIRCLE CELL^TM used a high pressure micro-flow-through sampling accessory fitted with a ZnSe internal reflection element. Peak heights were evaluated with the Nicolet SUPER QUANT program after spectral subtraction of the solvent. TheP=0 stretching absorption band, centered around 1240 cm^–1 for theG-type agents and 1180 cm^–1 for VX, produced good quantification. At a concentration of 2.0 mg/ml for theG-type agents and 1.0 mg/ml for VX, quantitative analysis produced coefficients of variation of 3% or less. The detection limit was observed to be around 0.1 mg/ml.This work was performed at the US Army Medical Research Institute of Chemical Defense and funded by the US Army Medical Research and Development Command under the provisions of the Intergovernmental Personnel Act of 1970 (P.L. 91-648).The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense     

水和粮食中化学战剂的分析

建立了水和粮食中７种化学战剂沙林、棱曼、塔崩、甲氟膦酸环已酯、Ｓ－（２＝－二惜内基氨乙基）甲基硫直膦酸乙酯（ＶＸ）、俄罗期ＶＸ和芥子气的ＧＣ、璃子选择＿分析方法。染毒水样经二氯甲烷提取,提取液在氮气流下浓缩至１ｍＬ;染毒粮样用蒸馏水提取,提取液离心后过Ｃ１８固相柱,乙腈洗脱,然后用ＧＣ－ＭＳ－ＳＩＭ测定。该法前处理较简便,净化效果好,方法灵敏,适用于军粮、饮水中微量化学战剂的分析。