Chomping on uranium

Science News,  Feb 9, 2008  by Davide Castelvecchi

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To a chemist's eye, uranium has always looked dull. Not anymore.

Natural uranium mostly occurs as an oxide. In water, the oxide readily dissolves in the form of a uranyl ion--a positively charged molecule made of one uranium and two oxygen atoms. In this respect, uranium behaves similarly to lighter metals such as molybdenum and tungsten.

But while most metal oxides are highly reactive, uranyl is shy, chemically speaking, and extremely stable. It's harder to clean from toxic spills, for example, because it won't react with or bind to much at all.

Polly Arnold and Jason Love of the University of Edinburgh in Scotland and their collaborators have brought out uranyl's more outgoing side. They have coaxed uranyl to become reactive in an organic liquid by "biting" it with a mouth-shaped molecule. The molecule captures the uranyl in its jaw, Arnold explains, with one of the oxygen atoms sticking up toward the palate--a sort of Pac-Man with a tongue piercing, she says, referring to the 1980s videogame.

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Pressed to the mole cule's palate, the oxygen is forced to donate electrons to potassium atoms. This transfer throws off uranyl's balance, allowing its other oxygen end--which pierces through Pac-Man's jaw and sticks out the other side--to react with silicon-based compounds dissolved in the solution, the authors report in the Jan. 17 Nature.

Directing uranyl's behavior could have other uses. Lighter metal oxides are "famously good" as catalysts, Arnold says. Thanks to uranium's complex structure, new, uranyl-based catalysts might enable novel reactions, such as the cheap conversion of natural gas into liquid fuels that would be easier to transport, Arnold says.

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