MOF Catalyst Quickly Disables Chemical Warfare Agents

Researchers in the US have found a metal-organic framework (MOF) that has the potential to rapidly break down nerve agents, thus providing a possible tool for destroying chemical weapons.

Chemical weapons based on organophosphate nerve agents, such as sarin (GB), soman (GD) and tabun (GA) have been extensively synthesised and used long since World War I. Sarin is among the most toxic and fast-acting chemical weapons. Exposure can cause death within minutes unless a suitable antidote is administrated.
In August 2013, a chemical attack in the suburbs of Damascus, Syria, lead to the death of an estimated 1500 civilians. This tragic event demonstrates the harsh consequences of using these lethal organophosphates.

Vast efforts have been placed into developing modified activated carbons or metal oxides suitable for absorbing or chemically altering these nerve agents. These methods are widely used today in gas mask filters, however only provide a certain measure of protection as a result of low capacity and slow degradation kinetics.
Hence, a material which possesses the ability to instantaneous hydrolyse these nerve-agent simulants is long sought after.

MOFs are porous crystalline materials composed of metal ions or clusters as centres and organic molecule ligands as linking groups.

Scientists in the US have found a new MOF which possesses the ability to rapidly hydrolyse and consequently destroy the nerve-agent simulants. The study, led by Omar Farha, at Northwestern University used a zirconium-based MOF as a catalyst to hydrolyse a phosphate ester-based nerve-agent simulant. The zirconium-based MOFs are particularly promising candidates for hydrolysis catalysts due to their great aqueous stability over a wide range of pHs. The zirconium-based MOF comprises uncommonly wide channels (31 Å). These larger channels allow for the organophosphates to access the internal catalytic sites, where the Lewis acidic Zr (IV) centres decompose the molecules via hydrolysis.

Through their study, Professor Farha and his colleagues were able to accelerate the hydrolysis of dimethyl-4-nitrophenyl phosphate (DMNP), a nerve-agent simulant. The hydrolysis of DMNP in the presence of this new MOF-based catalyst was almost instantaneous and the catalyst possessed the ability to convert all of the DMNP into a safe dimethoxy phosphate anion within 30s. Further to this, the catalyst maintained its efficiency when the simulant was pumped through a filter containing the MOF.

Faraha and his team suggest that the features shown by this rapidly-acting catalyst make the material promising for use in protective equipment worn by solidiers and could provide a quick means of destroying stockpiles of chemical weapons.

References:
S-Y Moon et al, Angew. Chem., Int. Ed., 2015, DOI: 10.1002/anie.201502155
M Gunther, RSC, Chemistry World, 2015, 05, MOF catalyst capable disabling chemical weapons

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Naomi Mann

Chemistry Undergraduate student, Cardiff.

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