Exploring the Effects of Node Topology, Connectivity, and Metal Identity on the Binding of Nerve Agents and Their Hydrolysis Products in Metal-Organic Frameworks

Advancing Metal-Organic Framework-Based Composites for Effective Chemical Warfare Agent Detoxification under Real-World Conditions

Threats from toxic chemical warfare agents (CWAs) persist due to war and terrorist attacks, endangering both human beings and the environment. Metal-organic frameworks (MOFs), which feature ordered pore structures and excellent tunability at both metal/metal cluster nodes and organic linkers, are regarded as the best candidates to directly remove CWAs and their simulants via both physical adsorption and chemically catalyzed hydrolysis or oxidization. MOFs have attracted significant attention in the last two decades that has resulted from the rapid development of MOF-based materials in both fundamental research and real-world applications. In this review, the authors focus on the recent advancements in designing and constructing functional MOF-based materials toward CWAs detoxification and discuss how to bridge the gap between fundamental science and real-world applications. With detailed summaries from different points of view, this review provides insights into design rules for developing next-generation MOF-based materials for protection from both organophosphorus and organosulfur CWAs to mitigate potential threats from CWAs used in wars and terrorism attacks.

Fluoride Product Inhibition: New Insight into the Degradation of Nerve Agents by Zr-MOFs

Zirconium-based metal-organic frameworks (Zr-MOFs) have shown remarkable efficacy in catalytically degrading neurotoxic agents in recent years. However, the catalytic activity of Zr-MOFs can be inhibited due to the binding of phosphate degradation products to the Zr nodes. Here, we reported the inhibition effect of a nonphosphate substance, fluoride, which can deactivate Zr-MOF nodes for the degradation of GD and VX and simulate DEPPT. The experimental and theoretical calculation results reveal that the fluoride product during GD degradation shows much more significant suppression than phosphate. The phosphate products can depart from the Zr nodes completely by adding H2O molecules on the Zr nodes to reduce the energy barrier. However, the fluoride can replace the bridged μ3-OH groups and terminal -OH groups on Zr-oxo clusters irreversibly, changing the electric density of Zr nodes and eliminating the terminal -OH. Without the terminal -OH, the five-coordinate phosphorus intermediate cannot be formed, resulting in the inactivation of Zr-O-Zr sites. This study provides new insights into Zr-MOF catalyst deactivation mechanisms and may help to develop a new strategy to design MOFs with high anti-inhibition efficiency for the degradation of nerve agents.

Computational Analysis of Sarin, Soman, and Their Water Mixtures in NU-1000: Interaction Mechanisms, Distribution Patterns, and Pairing Effects

Due to their extraordinary structural stability under humid conditions, zirconium-based metal-organic frameworks (Zr-MOFs) have been widely investigated for the hydrolytic degradation of nerve agents. That said, mechanisms of hydrolysis in the solid state and the participation of environmental water are not well understood. This work utilizes computational techniques to evaluate the behavior of water and two organophosphorus nerve agents (sarin and soman) in NU-1000, a Zr-MOF with the characteristic attributes for hydrolytic efficiency under humid conditions. Density functional theory (DFT) calculations reveal that soman binds more favorably to NU-1000 active sites than sarin, resulting in different preferential locations of each nerve agent within the framework. The strength of nerve agent binding is also found to vary depending on the site environment, with more favorable binding of both nerve agents occurring in the c-pores of NU-1000 than in the mesopores. Molecular dynamics (MD) simulation results further illustrate that free water molecules in NU-1000 prioritize interactions with nerve agents. Given the variation in their affinity for active site interactions, the introduction of different nerve agents to the framework results in substantial differences in water distribution and behavior. The results give insight into potential variances in the functionality of NU-1000 toward the hydrolysis of each nerve agent. More importantly, they emphasize the significance of considering the role of environmental water in hydrolysis and the possibility of diverse reaction variables based on the type of nerve agent and the properties of the MOF.

Designed Metal-Containing Peptoid Membranes as Enzyme Mimetics for Catalytic Organophosphate Degradation

The detoxification of lethal organophosphate (OP) residues in the environment is crucial to prevent human exposure and protect modern society. Despite serving as excellent catalysts for OP degradation, natural enzymes require costly preparation and readily deactivate upon exposure to environmental conditions. Herein, we designed and prepared a series of phosphotriesterase mimics based on stable, self-assembled peptoid membranes to overcome these limitations of the enzymes and effectively catalyze the hydrolysis of dimethyl p-nitrophenyl phosphate (DMNP)─a nerve agent simulant. By covalently attaching metal-binding ligands to peptoid N-termini, we attained enzyme mimetics in the form of surface-functionalized crystalline nanomembranes. These nanomembranes display a precisely controlled arrangement of coordinated metal ions, which resemble the active sites found in phosphotriesterases to promote DMNP hydrolysis. Moreover, using these highly programmable peptoid nanomembranes allows for tuning the local chemical environment of the coordinated metal ion to achieve enhanced hydrolysis activity. Among the crystalline membranes that are active for DMNP degradation, those assembled from peptoids containing bis-quinoline ligands with an adjacent phenyl side chain showed the highest hydrolytic activity with a 219-fold rate acceleration over the background, demonstrating the important role of the hydrophobic environment in proximity to the active sites. Furthermore, these membranes exhibited remarkable stability and were able to retain their catalytic activity after heating to 60 °C and after multiple uses. This work provides insights into the principal features to construct a new class of biomimetic materials with high catalytic efficiency, cost-effectiveness, and reusability applied in nerve agent detoxification.

Advances in Metal-Organic Frameworks for the Removal of Chemical Warfare Agents: Insights into Hydrolysis and Oxidation Reaction Mechanisms

The destruction of chemical warfare agents (CWAs) is a crucial area of research due to the ongoing evolution of toxic chemicals. Metal-organic frameworks (MOFs), a class of porous crystalline solids, have emerged as promising materials for this purpose. Their remarkable porosity and large surface areas enable superior adsorption, reactivity, and catalytic abilities, making them ideal for capturing and decomposing target species. Moreover, the tunable networks of MOFs allow customization of their chemical functionalities, making them practicable in personal protective equipment and adjustable to dynamic environments. This review paper focuses on experimental and computational studies investigating the removal of CWAs by MOFs, specifically emphasizing the removal of nerve agents (GB, GD, and VX) via hydrolysis and sulfur mustard (HD) via selective photooxidation. Among the different MOFs, zirconium-based MOFs exhibit extraordinary structural stability and reusability, rendering them the most promising materials for the hydrolytic and photooxidative degradation of CWAs. Accordingly, this work primarily concentrates on exploring the intrinsic catalytic reaction mechanisms in Zr-MOFs through first-principles approximations, as well as the design of efficient degradation strategies in the aqueous and solid phases through the establishment of Zr-MOF structure-property relationships. Recent progress in the tuning and functionalization of MOFs is also examined, aiming to enhance practical CWA removal under realistic battlefield conditions. By providing a comprehensive overview of experimental findings and computational insights, this review paper contributes to the advancement of MOF-based strategies for the destruction of CWAs and highlights the potential of these materials to address the challenges associated with chemical warfare.

Effective Degradation of Novichok Nerve Agents by the Zirconium Metal-Organic Framework MOF-808

Novichoks are a novel class of nerve agents (also referred to as the A-series) that were employed in several poisonings over the last few years. This calls for the development of novel countermeasures that can be applied in protective concepts (e.g., protective clothing) or in decontamination methods. The Zr metal-organic framework MOF-808 has recently emerged as a promising catalyst in the hydrolysis of the V- and G-series of nerve agents as well as their simulants. In this paper, we report a detailed study of the degradation of three Novichok agents by MOF-808 in buffers with varying pH. MOF-808 is revealed to be a highly efficient and regenerable catalyst for Novichok agent hydrolysis under basic conditions. In contrast to the V- and G-series of agents, degradation of Novichoks is demonstrated to proceed in two consecutive hydrolysis steps. Initial extremely rapid P-F bond breaking is followed by MOF-catalyzed removal of the amidine group from the intermediate product. The intermediate thus acted as a competitive substrate that was rate-determining for the whole two-step degradation route. Under acidic conditions, the amidine group in Novichok A-230 is more rapidly hydrolyzed than the P-F bond, giving rise to another moderately toxic intermediate. This intermediate could in turn be efficiently hydrolyzed by MOF-808 under basic conditions. These experimental observations were corroborated by density functional theory calculations to shed light on molecular mechanisms.

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.

Enhancing the Catalytic Activity of MOF-808 Towards Peptide Bond Hydrolysis through Synthetic Modulations

The performance of MOFs in catalysis is largely derived from structural features, and much work has focused on introducing structural changes such as defects or ligand functionalisation to boost the reactivity of the MOF. However, the effects of different parameters chosen for the synthesis on the catalytic reactivity of the resulting MOF remains poorly understood. Here, we evaluate the role of metal precursor on the reactivity of Zr-based MOF-808 towards hydrolysis of the peptide bond in the glycylglycine model substrate. In addition, the effect of synthesis temperature and duration has been investigated. Surprisingly, the metal precursor was found to have a large influence on the reactivity of the MOF, surpassing the effect of particle size or number of defects. Additionally, we show that by careful selection of the Zr-salt precursor and temperature used in MOF syntheses, equally active MOF catalysts could be obtained after a 20 minute synthesis compared to 24 h synthesis.

Role of Zr6 Metal Nodes in Zr-Based Metal-Organic Frameworks for Catalytic Detoxification of Pesticides

Pesticides are chemicals widely used for agricultural industry, despite their negative impact on health and environment. Although various methods have been developed for pesticide degradation to remedy such adverse effects, conventional materials often take hours to days for complete decomposition and are difficult to recycle. Here, we demonstrate the rapid degradation of organophosphate pesticides with a Zr-based metal-organic framework (MOF), showing complete degradation within 15 min. MOFs with different active site structures (Zr node connectivity and geometry) were compared, and a porphyrin-based MOF with six-connected Zr nodes showed remarkable degradation efficiency with half-lives of a few minutes. Such a high efficiency was further confirmed in a simple flow system for several cycles. This study reveals that MOFs can be highly potent heterogeneous catalysts for organophosphate pesticide degradation, suggesting that coordination geometry of the Zr node significantly influences the catalytic activity.

Tuning the Lewis acidity of metal-organic frameworks for enhanced catalysis

The kinetics of hydrolysis of dimethyl nitrophenyl phosphate (DMNP), a simulant of the nerve agent Soman, was studied and revealed transition metal salts as catalysts. The relative rates of DMNP hydrolysis by zirconium and hafnium chlorides are in accordance with their Lewis acidity. In situ conversion of zirconium chloride to zirconium oxy-hydroxide was identified as the key step. We propose a precursor-MOF activity relationship.