Buckybowls by the bucketful

Scientists may be closer to unlocking the mystery of buckyballs – hollow spheres formed by 60 atoms of carbon – thanks to research being conducted by Peter Rabideau, a senior chemist at the US Department of Energy's Ames Laboratory.

Using simple solution chemistry, Rabideau has developed a process to produce gram quantities of corannulene (C20), a curved-surface, aromatic hydrocarbon. Nicknamed buckybowls, the bowl-shaped corranulene molecules represent the polar cap of the C60 sphere. By making it possible to produce large quantities of these bowl segments, Rabideau hopes to eventually piece together a complete buckyball.

Buckyballs have intrigued chemists since the uniquely structured molecules were first discovered in 1985. The carbon atoms align to form a hollow structure similar to the pattern of panels found on a soccer ball. They get their name from Buckminster 'Bucky' Fuller, who pioneered the concept of geodesic domes.

Since the structure is very stable and hollow, chemists have envisioned a whole new array of applications if they could find a way to put other atoms or compounds inside the buckyball.

Unfortunately, the only way to produce C60 is to replicate the environment of interstellar space with a process that basically involves arcing carbon rods, but this reaction takes place only at high temperatures. The high temperatures make it hard to control, and therefore extremely difficult to try to make buckyballs with something inside them. So the search turned to finding a way to 'build' a buckyball from scratch.

'If you took a buckyball apart, it wouldn't be a stable entity because it would have dangling bonds,' Rabideau said. 'But if you took it apart and put hydrogen atoms on the dangling bonds to stabilise it, you'd have a chemical compound that we call a buckybowl.'

The polynuclear aromatic hydrocarbon corannulene (C20) was first synthesized in 1966 at the University of Michigan by a long and difficult 17-step process that produced quantities weighing just a few milligrams. Then in the early 90's, another group of researchers synthesised corannulene using pyrolysis.

'The problem with this technique is that you must do it in vacuum, so by definition you're still working with very small amounts of material,' Rabideau said.

What Rabideau and fellow researcher Andrzej Sygula developed was a solution-phase synthesis using dilute sodium hydroxide in water and acetone that produces tetrabromocorranulene. This process allows production of 25-gram samples, a thousand-fold increase over the pyrolysis method.

Though building a buckyball is still in the distance, researchers now have an unlimited supply of bowl material to study. By unlocking the properties of these bowl-shaped compounds, Rabideau hopes to eventually discover a way to combine the bowls into a sphere.

'If we could figure out a few critical reactions, we might ultimately be able to synthesise C60,' Rabideau said. 'That would, in principle, allow us to build C60 with a hole in it so that we could trap something inside, such as an atom or metal, and then close the ball.'