Lists of Chemical Warfare Agents and Precursors from International Nonproliferation Frameworks: Structural Annotation and Chemical Fingerprint Analysis

Molecular modeling of Mannich phenols as reactivators of human acetylcholinesterase inhibited by A-series nerve agents

The A-series is the most recent generation of chemical warfare nerve agents (CWA) which act directly on the inhibition of the human acetylcholinesterase (HssAChE) enzyme. These compounds lack accurate experimental data on their physicochemical properties, and there is no evidence that traditional antidotes effectively reactivate HssAChE inhibited by them. In the search for potential antidotes, we employed virtual screening, molecular docking, and molecular dynamics (MD) simulations for the theoretical assessment of the performance of a library of Mannich phenols as potential reactivators of HssAChE inhibited by the Novichok agents A-230, A-232, and A-234, in comparison with the commercial oximes pralidoxime (2-PAM), asoxime (HI-6), trimedoxime (TMB-4), and obidoxime. Following the near-attack conformation (NAC) approach, our results suggest that the compounds assessed would face difficulties in triggering the proposed nucleophilic in-line displacement mechanism. Despite this, it was observed that certain Mannich phenols presented similar or superior results to those obtained by reference oximes against A-232 and A-234 model, suggesting that these compounds can adopt more favourable conformations. Additional binding energy calculations confirmed the stability of the model/ligands complexes and the reactivating potential observed in the molecular docking and MD studies. Our findings indicate that the Mannich phenols could be alternative antidotes and that their efficacy should be evaluated experimentally against the A-series CWA.

Expanding the Australia Group’s chemical weapons precursors control list with a family-based approach

The Australia Group (AG) is a forum of like-minded states seeking to harmonize export controls to prevent the proliferation of chemical and biological weapons. The AG Chemical Weapons Precursors list features dual-use chemicals that can be used as precursors for the synthesis of chemical weapons, all individually enumerated. This is in contrast with the Chemical Weapons Convention (CWC) Schedules, which, alongside entries describing discrete chemicals, also include entries that describe families of chemicals. By using families of chemicals, the CWC achieves the objective of covering with a single entry a wide array of related chemicals of concern, including chemicals that have not yet been made. There are practical reasons why the AG Chemical Weapons Precursors list is exclusively based on the enumeration of individual chemicals. A cheminformatics tool of which we have developed a prototype, the Nonproliferation Compliance Cheminformatics Tool (NCCT), has the potential to enable export control officers to handle control lists that contain families of chemicals. Thus, it opens the way to expand the AG Chemical Weapons Precursors list to a family-based approach for some of its entries. Such a change would result in a closer alignment of the chemical space covered by the AG Chemical Weapons Precursors list with that covered by the CWC Schedules, thus closing loopholes that could be exploited by proliferators.

Feasible Detoxification Coating Material for Chemical Warfare Agents Using Poly(methyl methacrylate)-Branched Poly(ethyleneimine) Copolymer and Metal-Organic Framework Composites

Defense against chemical warfare agents (CWAs) is regarded as a top priority for the protection of humanity, but it still depends on physical protection with severe limitations such as residual toxicity and post-treatment requirement. In this study, a strategically designed functional polymeric substrate was composited with a metal-organic framework catalyst to remove toxicity immediately. A series of PMMA-BPEI copolymers exhibited high processability as a coating and accelerated the catalytic activity of Zr(IV)-based metal-organic framework catalysts (UiO-66). Among them, PMB12_40 composite coating on a cotton fabric, containing a PMMA-BPEI copolymer (PMMA/BPEI = 1/2) and 40% of UiO-66 catalyst, can efficiently decompose nerve agent simulants (methyl-paraoxon) under both liquid phase (t1/2 = 0.14 h) and humidified (t1/2 = 4.8 h) conditions. Moreover, a real agent, GD, was decomposed 100% by PMB12_40 in 4 h at 25 °C and 65% relative humidity. On the basis of superior catalytic activity, the PMB composites are anticipated to be a potential material for active chemical protection coating.

Supporting the fight against the proliferation of chemical weapons through cheminformatics

International frameworks have been put in place to foster chemical weapons nonproliferation and disarmament. These frameworks feature lists of chemicals that can be used as chemical weapons or precursors for their synthesis (CW-control lists). In these lists, chemicals of concern are described through chemical names and CAS Registry Numbers®. Importantly, in some CW-control lists, some entries, rather than specifying individual chemicals, describe families of related chemicals. Working with CW-control lists poses challenges for frontline customs and export control officers implementing these frameworks. Entries that describe families of chemicals are not easy to interpret, especially for non-chemists. Moreover, synonyms and chemical variants complicate the issue of checking CW-control lists through names and registry numbers. To ameliorate these problems, we have developed a functioning prototype of a cheminformatics tool that automates the task of assessing whether a chemical is part of a CW-control list. The tool, dubbed the Nonproliferation Cheminformatics Compliance Tool (NCCT), is a database management system (based on ChemAxon’s Instant JChem) with an embedded database of chemical structures. The key feature of the database is that it contains not only the structures of the individually listed chemicals, but also the generic structures that describe the entries relative to families of chemicals (Markush structures).

Unambiguous identification and determination of A234-Novichok nerve agent biomarkers in biological fluids using GC-MS/MS and LC-MS/MS

The present study was intended to develop suitable methods for unambiguous identification and determination of ethyl (1-(diethylamino)ethylidene) phosphoramidofluoridate (known as A234-Novichok) biomarkers in urine and plasma samples. Multiple biomarkers were investigated for the first time, to verify intoxication by the A234-Novichok agent, using sensitive and accurate techniques including gas and liquid chromatography-tandem mass spectrometry (GC-MS/MS and LC-MS/MS). Like other nerve agents, in biological matrices, the A234-Novichok agent reacts with several proteins to form related adducts. Considering this, two different protein adduct biomarkers in blood samples were analyzed, and the regenerated A234 was determined. Two-dimensional chromatography and solid-phase extraction techniques were employed for blood sample preparation. Limits of detection for butyrylcholinesterase (BChE) adduct, the regenerated A234, and albumin covalent adduct were determined and reported as 1, 1, and 10 ng mL^-1, while the related calibration curves were linear within the range of 2-100, 2-100, and 15-100 ng mL^-1, respectively. The detection limit and linear range for the intact agent in the urine sample were determined as 0.1 and 1-100 ng mL^-1, respectively. Since A234 and some other Novichok chemicals have been added to the Schedule 1 of the Chemical Weapons Convention (CWC), Annex on Chemicals, after UK incidents, the analytical methods developed in this work might be used for verification purposes, as well as OPCW Biomedical Proficiency Tests.

Reducing health & environmental impacts of chemical warfare agents: Computational chemistry contributions

This review article summarizes advances in computational chemistry and cheminformatics methods and techniques that are used or have potential for use in reducing health and environmental impacts of Chemical Warfare Agents (CWA). These methods, include, but are not limited to, predictive modeling, data mining and virtual screening, similarity searching, molecular docking and dynamics and are briefly presented here. Applications of these in silico approaches, specifically for the protection of personnel and civilians against CWA, but also beyond, are discussed. CWA include toxic chemicals that can cause death, injury, or temporary incapacitation through their chemical action. CWA impose a significant worldwide threat and as such, destruction, remediation as well as protection measurements need to be carefully designed. Towards this goal computational chemistry and cheminformatics can play a key role specifically as far as decontamination, risk assessment and risk management are concerned. Among the wide range of in silico techniques applied for CWA, specific previously published paradigms are presented, including toxicity and property prediction, CWA simulant identification and CWA detoxification. Beyond CWA research, other applications with military interest are briefly presented and emerging trends of potential relevance noted.

Hydrolysis of methylphosphonic anhydride solid to methylphosphonic acid probed by Raman and infrared reflectance spectroscopies

Much is still unknown about the mechanisms and rates of environmental degradation of organophosphorous pesticides and agents. In this study we focus on the degradation of one organophosphorous compound, namely solid methylphosphonic anhydride [CH₃P(O)OHOP(O)OHCH₃, MPAN] and its rate of conversion to methylphosphonic acid (MPA) via heterogeneous hydrolysis. Pure MPAN was synthesized and loaded in open sample cups placed inside exposure chambers containing saturated salt solutions to control the relative humidity (RH). The reaction was monitored in the sample cup at various times using both infrared hemispherical reflectance (HRF) spectroscopy and Raman spectroscopy. Calibrated HRF and Raman spectra of both pure reagents as well as gravimetrically prepared mixtures were used to quantify the concentrations of MPAN and MPA throughout the reaction. Results show both HRF and Raman spectroscopies are convenient non-invasive methods for detection of solid chemicals as long as a large area is sampled to average out any spatial inhomogeneities that occur on the sample surface and minimal phase changes occur during the course of the reaction. The samples for the 54 and 75% RH studies showed significant deliquescence, and the liquid water had to be removed prior to measurement; this effect led to differences in the sample form, such that the calibration spectra were no longer valid for quantitative analysis using HRF spectroscopy. Raman spectroscopy, on the other hand, proved to be less sensitive to these effects and provided better estimation of the MPAN and MPA concentrations. The MPAN degradation rate displayed a very strong dependence on relative humidity: at room temperature the reaction showed 50% conversion of the MPAN in 761 ± 54 h at 33% RH, 33 ± 4 h at 43% RH, 17 ± 2 h at 54% RH and just 7 ± 1 h at 75% RH.