Metal-organic framework quickly destroys toxic nerve agents
The organic ligand gives the material its important structure by connecting the nodes, but it does not participate in the catalysis of the nerve agent.
The zirconium node selectively clips the phosphate-ester bond in the nerve agent, rendering it innocuous. With the critical bond broken, the rest of the molecule is left alone. The bond is broken through the process of hydrolysis, a reaction involving the breaking of a molecule’s bond using water. The MOF can use the humidity in the air.
The release notes that in their study, the researchers first tested their catalyst against a GD simulant, called DMNP, and found the MOF degraded half of the target in less than 1.5 minutes. Next, they tested the MOF against GD and found the catalyst degraded half of the nerve agent in less than three minutes. These half-lives are very impressive, Farha said, and show how well the catalyst is working.
They also tested the zirconium cluster alone, without the cluster being in the MOF structure, and the catalyst was not as effective at degrading the nerve agent. This shows the importance of the MOF scaffold.
The research team’s experimental and computational results suggest that the extraordinary activity of NU-1000 comes from the unique zirconium node and the MOF structure that allows the material to engage with more of the nerve agent and to destroy it. The researchers expect the MOF to be effective against other easy-to-make chemical warfare agents with phosphate-ester bonds, such as VX.
NU-1000 is inspired by the enzyme phosphotriesterase, which is found in bacteria. The natural enzyme has two zinc ions bridged by a hydroxyl group as the active catalytic site.
Farha and his colleagues wanted to make a much more potent and stable catalyst, so they used zirconium ions instead of zinc.
“We are learning from nature, but trying to do better by making more robust materials,” Farha said. “The natural enzyme does precisely the same chemistry, but its lifetime is very short — it cannot survive under the conditions soldiers are deployed in.”
Even though the synthetic catalyst yields the same weapons-degradation product as the enzyme, it does so by a means that is much less dependent on the exact structure and composition of the chemical weapon target. The next step, therefore, is to determine the extent to which the artificial catalyst functions as a broad-spectrum catalyst.
Farha added, “Our catalyst is fantastic compared to other catalysts, but there is still more work to be done.”
— Read more in Joseph E. Mondloch et al., “Metal-organic framework destroys common toxic nerve agents quickly,” Nature Materials (16 March 2015) (doi:10.1038/nmat4238)
