Molecular games

CHEMISTS who don't find enough time for the field or courts can now take vicarious pleasure in "shooting" and "smashing" molecular soccer and tennis balls. Already well-known is the 60-carbon-atom buckminster fullerene molecule, the soccer ball look-alike. But the molecular tennis ball is a newcomer.

Except for their athletic connection, the two molecules have little in common. Fullerenes are formed when several simple carbon units link up in the flame of an electric arc whereas molecular tennis balls take shape when two complex molecular components meet and stitch themselves together in a solution, just like the two segments of a tennis ball.

Their uses, too, are different. Fullerenes are valued for their unique electronic and chemical properties, but the molecular tennis balls can be most valuable as containers for other compounds, especially drugs, say their creators, Julius Rebek, Ren Wyler and R Branda of the Massachusetts Institute of Technology. Just as viruses slip into cells and release their DNA, the "artificial virus", as Rebek calls their virus-sized tennis balls, could encapsulate drugs and smuggle them into cells.

Though most of the molecules of drugs are large, Rebek and his colleagues have designed molecular tennis balls that can trap the small molecules of methane (Science, Vol 263, No 5151). The team is now working on developing larger capsules -- dubbed molecular softballs -- that have the same simple structure.

More than its potential application as an artificial virus, the sheer elegance by which this molecule self-assembles has brought the scientists accolades. The technique does not require complicated chemical synthesis or extreme conditions. The chemists have designed the molecule in such a manner that its two parts can link up together only in one way: as a spherical cage.

Meanwhile, some scientists are looking for ways to make the artificial virus trigger a drug-spill within the cell at the right time. One scheme entails attaching carboxylic acid groups to the outside of the spheres, which will burst open the blob and release its contents when the surroundings become more alkaline.

But Rebek wants to go a step further and make molecules that can replicate by themselves like real viruses, which use host cells to make copies of their own genetic material. If drug molecules can be made to emulate this feat, say scientists, a small amount could be made to duplicate themselves, making the administration of higher doses unnecessary.

Science & Technology