US researchers have added another string to the proverbial bow of metal organic framework (MOF) materials showing that these compounds might be useful in breaking down lethal nerve agents. Omar Farha and his colleagues from Northwestern University and the University of Minnesota have demonstrated how a zirconium-based MOF takes just minutes to degrade Soman (GD), a more toxic chemical cousin of sarin. Moreover, their computer simulations show the same material - NU-1000 - should be effective against the likes of VX and other compounds. The plan would be to incorporate the porous material into protective gas masks as well as being used in bulk to destroy stockpiled chemical weapons.
"This designed material is thermally and chemically robust, and it doesn't care what conditions it is in", explains 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." [Farha et al., Nature Mater, 2015, online; DOI: 10.1038/NMAT4238]
Farha points out that GD and VX are not particularly complicated molecules and they can be rendered non-lethal by simple chemical changes that can be achieved rapidly and catalytically by their MOF. Specifically, the metal nodes in NU-1000 cleave the phosphate-ester bonds in the nerve agent through hydrolysis, rendering it non-toxic.
Initially, the team tested NU-1000 on a relatively innocuous compound DMNP, dimethyl 4-nitrophenyl phosphate, to show how the MOF might degrade such compounds. The degradation half life was impressively under 90 seconds. When they tested GD itself the catalyst was slower, but still fast, degrading half the quantity of nerve agent in less than three minutes. As a control, the team tested the bare zirconium cluster from the heart of their MOF and found it to be far less effective in this form; the organic scaffold providing the necessary porous environment to make it work well.
NU-1000 was inspired by bacterial phosphotriesterases, which contain two zinc ions bridged by a hydroxyl group in their active site. "We are learning from nature, but trying to do better by making more robust materials, hence the use of zirconium rather than zinc," Farha explains. "The natural enzyme does precisely the same chemistry, but being a protein its lifetime is very short under the conditions in which soldiers are deployed. The team is now investigating how much of a broad-spectrum catalyst their MOF might be. "We believe the design rules we learned from this project will lead to using these materials in other catalytic application," Farha told Materials Today.
David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the popular science book "Deceived Wisdom".