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Stuffed buckyballs could mean clearer MRI scans
22 January 2005
From New Scientist Print Edition.
Celeste Biever

For the first time, a carbon buckyball has been ripped open, stuffed with a foreign molecule and then stitched up again.

This ability to lock up atoms or molecules, developed by Koichi Komatsu and his team from Kyoto University in Japan, could lead to buckyballs being used in a host of new ways. For example, they could form protective containers for the toxic metals that are administered to patients during medical imaging.

Until now, getting atoms inside the football-shaped 60-carbon molecules has proved difficult. The atoms of a small number of metals can be trapped in buckyball cages as they form by evaporating the metal with graphite. But the real prize would be the ability to lock up any atom at will, creating buckyball derivatives with useful properties. Certain metals might enhance the conductivity of buckyballs and make them magnetic, while encapsulating noble gases like xenon could enhance MRI scans.

Previously, Yves Rubin of the University of California in Los Angeles used chemicals to break some of a buckyball's bonds and form a hole in it. The chemicals then attached themselves to the molecule to hold the hole open, allowing foreign atoms or molecules to flow through it. But Rubin did not have a way to close the hole again.

Komatsu and his colleagues have developed a series of reactions that solve this problem. First they created holes in the carbon molecules big enough for hydrogen molecules to enter. The team then introduced hydrogen molecules by heating the open buckyballs with hydrogen gas at high pressure.

Once the hydrogen molecule was inside, the team removed the chemicals holding the hole open and sealed the cage to re-form a perfect buckyball with hydrogen trapped inside. Even when the cage is heated to 500 °C for 10 minutes, the hydrogen does not escape (Science, vol 307, p 238).

The hole is shrunk step by step and finally eliminated using a series of chemical reactions new to buckyball chemistry, says Komatsu. The first is the oxidation of a sulphur atom that holds the hole open, allowing the oxide to float away as a gas. The next reaction shrinks the hole by bonding two of the carbon atoms together across its centre and removing two oxygen atoms. Finally all the remaining atoms that hold the hole open are removed and carbon-carbon bonds are reformed when the structure is heated to 340 °C.

Rubin is impressed by Kamatsu's feat. "Closing the hole is really neat. We wanted to do the same thing," he says. "It's really a major breakthrough."

Komatsu says the ability to stuff buckyballs with a variety of chemical species could potentially be useful for building nanoscale electronic circuits. Buckyballs containing different metals might behave like transistors, and their conductivity and properties could be altered depending on the metal that is encapsulated, he says.

From issue 2483 of New Scientist magazine, 22 January 2005, page 22

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