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The potassium-atom mouth of an organic molecule grabs one of the oxygen atoms (red) in uranium dioxide.

P. L. Arnold et al., Nature 451, 315 (17 January 2008)

Can Pac-Man Save Us From Radioactive Waste?

If chemicals were people, uranium dioxide would be the guy standing alone with his drink at a party. The world's most commonly used radioactive substance--and its heaviest natural element--clutches its two oxygen atoms so tightly, it almost never reacts with other compounds. Now researchers report finding a way to pry one oxygen atom loose, potentially opening up safer ways to handle and dispose of this nuclear antisocialite.

Uranium's heavy atomic weight makes it radioactive but only weakly so. Its greatest hazard to the environment is that it's a toxic metal. Worse, uranium's chemistry makes it very difficult to remove from water, causing it to be a very persistent and dangerous pollutant. To make uranium more reactive, a team of U.K. researchers employed what they call a "Pac-Man" strategy--named for the popular 1980s video game. After testing many alternatives, the chemists found an organic molecule that clamps down--like Pac-Man--on one of uranium dioxide's oxygen atoms. This weakens uranium's grip on the other oxygen, the researchers report tomorrow in Nature, allowing it to react with one of the new molecule's silicon atoms.

It's only a first step, says lead author Polly Arnold of the University of Edinburgh, U.K. The resulting compound is not stable enough to be useful in waste disposal just yet, but the new insights about uranium chemistry could eventually pay off with new technologies, she says. For one, the new molecule might help environmental scientists discover novel ways of extracting uranium dissolved in contaminated water, which constitutes a large portion of uranium pollution.

The findings "constitute breakthrough research in this area," says chemist William Evans of the University of California, Irvine. This approach to making uranium reactive suggests new directions for attacking the element's inert nature and may "model the principles that lead to [uranium] degradation in nature," which remain unknown, he says.

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