While the Iran-Iraq war of 1981-1988 saw the only large-scale use of chemical weapons since WWII, in a world beset by rogue states, civil wars, and terrorism, protecting against nerve agents and disposing of them remains a major problem. One bright spot is a team from Northwestern University, which has developed a new material capable of neutralizing nerve gases. The zirconium-based Metal-Organic Framework (MOF) called NU-1000 is not only useful for disposing of stockpiles of such toxins, but also for use in gas masks and protective suits for soldiers and rescue workers.
Nerve gas is one of the most frightening of chemical weapons. First developed in Germany in 1936, nerve agents, as they are also called, are chemically simple, but extremely deadly. They consist of phosphorus-containing organic chemicals called organophosphates and work by blocking acetylcholinesterase, which disrupts nerve transmissions to the organs.
Be it sarin (GB), VX, Soman (GD), or a host of other agents, the result is a frightening succession of symptoms, often starting with a runny nose and quickly escalating to convulsions and complete respiratory failure unless quickly treated. They are absorbed through the skin as well as inhaled and are so dangerous in such small quantities that whole-body protection suits are needed by soldiers and responders, and disposal of stocks of nerve gas involve burning in complex plasma furnaces.
According to Northwest, NU-1000 simplifies protection and disposal of such agents. The team claims that the material is capable of degrading somar, a more dangerous version of sarin, rendering it harmless in a matter of minutes, and works under a wide variety of conditions, which makes it suitable for use on the battlefield.
"This designed material is very thermally and chemically robust, and it doesn’t care what conditions it is in," says team-leader Omar K. Farha. "The material can be in water or a very humid environment, at a temperature of 130 degrees or minus 15, or in a dust storm. A soldier should not need to worry about under what conditions his protective mask will work. We can put this new catalyst in rugged conditions, and it will work just fine."
NU-1000 was inspired by a natural enzyme, phosphotriesterase, which is produced by certain bacteria and works on the weak points in the nerve agents called phosphonate ester bonds. While the enzyme is effective, natural enzymes tend to be specialized and work in a narrow range of conditions, so the Northwestern team had to develop something in the form on of an inorganic catalyst that is more robust and capable of working on a wide range of molecular structures.
In NU-1000, metal-organic frameworks form a porous lattice structure that holds the agents to give the catalyst time to work. In the lattice are zirconium nodes, which form the catalyst. When the nerve agent is trapped in the lattice, it encounters the zirconium, which breaks the phosphate-ester bond in the molecule, changing it from a deadly poison to a harmless chemical in minutes through a process of hydrolysis. This means the reaction needs water to break the bonds, but the team says that humidity in the air is sufficient. Tests with a GD simulant chemical indicates that the lattice is important to the reaction. Using the zirconium alone proved to be much less effective.
According to the team, computer simulations indicate that NU-1000 should also be effective against other agents, such as VX. They are currently working on a broad-spectrum catalyst that can work on a wider variety of nerve agents.
The team's results were published in Nature Materials.
Source: Northwestern University
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