991028-1 10.1038/nsu991028-1 22 October 1999 technology taking the bite out of mustard gas PhilipBall

"Dim, through the misty panes and thick green light/As under a green sea, I saw him drowning."

The mustard gas molecule; simple but deadly
The horror of chemical warfare, so vividly captured in Wilfred Owen's description of a gas attack in the First World War, still haunts the world. Now chemists at the University of Wyoming have devised a system that simultaneously destroys and signals the presence of one of the first and most notorious of chemical weapons: mustard gas.

The 'green' of Owen's poem suggests a chlorine-gas attack, but mustard gas is even nastier. It was first used in 1917 near Ypres in Flanders, and causes terrible blistering and blindness, even death if it attacks the lung lining. Relatively easy to make, it is a common component in the arsenals of countries with chemical weapons. It featured amongst the chemical agents uncovered in Iraq by the Gulf War of 1991, and stockpiles there are still being destroyed. Some of the symptoms of Gulf War syndrome suggest exposure to mustard gas.

Various protective measures now exist against the gas. Clothing made from certain rubbery materials will keep it out, for example, and its effects can be alleviated with drugs. But only recently was an effective test developed that identifies an individual's exposure to mustard gas. Now David Jaeger and colleagues at Wyoming have created a chemical system that signals the presence of the compound, and at the same time, breaks it down.

Their solution, described in the journal Langmuir1, is to make little packages of 'signalling molecules' wrapped in a fabric that itself both reacts with and destroys the chemical agent. As the fabric of the packages is disrupted by the reaction, the signalling molecules are released to provide a tell-tale indicator of the agent's presence.

The packages are tiny hollow compartments called vesicles, miniature balloons about the same size as a single human cell. Like real cells, they are made from soap-like molecules. These molecules, called 'surfactants', clump together in sheets. A vesicle is made from two sheets stacked back to back and curled up on themselves.

The researchers devised surfactants that react with mustard gas – or in this case, with a very similar compound which simulates the real thing without being quite so dangerous. They let the surfactants form vesicles in the presence of a soluble dye, some of which becomes trapped inside the compartments.

When the dye-containing vesicles are exposed to the mustard-gas imitator, their walls erode away as the building blocks react with the poison to render them more innocuous. This allows the dye to leak out, colouring the solution and so indicating the not only the presence, but the abundance of the gas.

Once optimized, this system might be used, for example, as a portable kit with which United Nations chemical-weapons inspectors could identify toxic agents on site without risk of releasing them into the environment.

Jaeger, D. A., Schilling III, C. L., Zelenin, A. K., Li, B. & Kubicz-Loring, E. Reaction of a Vesicular Functionalized Surfactant with 2-Chloroethyl Phenyl Sulfide, a Mustard Simulant. Langmuir 1571807185 1999.