A CHEMICAL cage that safely traps white phosphorus could one day help clean up areas contaminated with the highly unstable substance. 鈥淭his cage could potentially be used in an industrial spill or a war zone,鈥� says lead researcher at the University of Cambridge.
鈥淭he iron cage could be used to clean up white phosphorus in an industrial spill or a war zone鈥�
White phosphorus, a highly reactive form of the element, is made of four phosphorus atoms linked together in the shape of a tetrahedron. It reacts violently with oxygen and is the active ingredient in numerous explosive devices, including incendiary bombs, smoke bombs and mortar rounds.
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Nitschke and his colleagues did not set out to produce a cage for phosphorus; they were investigating ways to get complex molecular structures to self-assemble. As part of this work, they created a cage made of four iron atoms linked together by rigid organic molecules to form a large tetrahedron with a central cavity.
鈥淎fter measuring the size of this cavity, we thought about what kinds of molecules would fit within,鈥� says Nitschke. 鈥淲hite phosphorus seemed to fit the bill.鈥� Sure enough, when the researchers mixed white phosphorus with a solution of these cages, they found that a single molecule of white phosphorus fitted snugly inside each cage ().
So snug is this fit that there is no room for oxygen atoms, meaning no reaction can take place. Nitschke found he could safely leave a solution of caged white phosphorus open to the air for months.
The white phosphorus can be removed from its cage by adding the organic solvent benzene to the solution. The benzene molecules readily push the white phosphorus out of the cage and takes its place.
, a chemistry professor at the University of California, Berkeley, points out that tetrahedron structures for housing molecules have been produced before, by his own group and others. 鈥淲hat I think is really exciting is the inclusion of [white phosphorus] as a guest,鈥� he says. 鈥淗ere we have Greek fire put in a bottle.鈥�
Nitschke is now looking to use the same approach to trap other molecules. 鈥淲e have recently succeeded in making bigger cages,鈥� he says. 鈥淢any interesting molecules, such as pharmaceuticals, are too big to fit in our phosphorus-binding cage, but could fit nicely in our next-generation cages.鈥�
