Science / Medicine : On a Roll With Spherical Carbon : Chemistry: Many uses are being explored for the molecules, nicknamed ‘buckyballs’ after Buckminster Fuller, whose geodesic domes resemble the substance’s shape.
A molecule in the shape of . . . a soccer ball?
“This is the biggest news in chemistry that I could have imagined,” says Robert Whetten of UCLA. Richard Smalley of Rice University, discoverer of the molecule, adds that “there’s hardly any area of chemistry this doesn’t touch. To a chemist it’s like Christmas.”
The cause for the excitement is a new form of carbon. Carbon is among the most versatile elements, the basis of life, the basis for plastics, pharmaceuticals and petrochemicals. Yet despite the immense variety of substances that contain it, carbon itself has been known to exist in only two fundamental forms: graphite, used in pencil lead, and diamonds.
Now, however, there is a third such form: buckyballs. These consist of nearly spherical molecules, each with 60 carbon atoms.
“This is the roundest of all molecules,” Smalley says. “The maximum number of objects you can arrange around a sphere, and have each be identical to every other, is 60.” This results from a theorem in geometry.
Indeed, the atoms of a buckyball group themselves into an array of 12 pentagons and 20 hexagons. Each atom lies at a juncture between two hexagons and a pentagon, giving the molecule its soccer ball shape.
Smalley first proposed this shape in 1985, constructing it with paper and scissors while working in his kitchen. It looked to him like one of the geodesic domes invented by Buckminster Fuller, so he christened it buckministerfullerene--a name that soon was shortened to buckyballs. Another of his sobriquets, fullerenes, would refer to an entire class of buckyball-like molecules having other than 60 atoms.
But at the time, buckyballs could only be made in minuscule quantities. This brought what Smalley calls “the search for the yellow vial.” Theory had predicted that the way in which the molecule absorbs light would make it appear yellow.
This search gained success during 1990. Donald Huffman of the University of Arizona, along with Wolfgang Kraetschmer of Germany’s Max Planck Institute for Nuclear Physics, introduced a technique to produce buckyballs in amounts as large as a chemist might need. Huffman recalls that May of last year was “the historic time” when he first prepared crystalline buckyballs. Sure enough, their color was yellow.
OK, so scientists can make buckyballs, and make a lot of them--so what? At the moment, buckyballs are entirely a topic for research, with applications in technology still lying somewhere off in the future. But the range of research topics illustrates the varied uses that this new form of carbon may see, and the diversity of reasons for which buckyballs may become significant.
This diversity includes medical uses, prospects for new batteries and new catalysts for use in the chemical industry, new lubricants and possibly even superconductivity.
At UCLA, an ongoing theme in the research is the behavior of buckyballs when exposed to light. The molecules can gain energy, attain an excited state--and then transfer this excitation to molecules of oxygen, which thus enter an energy-rich condition known as the singlet state. Because singlet oxygen is toxic to human cells, this property may make buckyballs applicable in cancer research.
Francois Dieterich of UCLA is supplying samples of buckyballs to various medical researchers, at the City of Hope and elsewhere, to see if it’s possible to concentrate the buckyballs within a tumor, feed these molecules with oxygen, and shine light on them to add the energy. Then, he suggests, “you could produce singlet oxygen at that position to destroy the tumor,” by killing its cells.
Preliminary indications suggest that buckyballs, other fullerenes, or compounds made from such molecules are more effective in this quest than another substance being tested called porphyrins.
At Rice University, Smalley believes that potentially the most important application of fullerene chemistry would be to open holes in the molecules and insert atoms of metals or other elements. He believes that such modified buckyballs would offer a new approach in seeking a lightweight storage battery such as might be suitable for an electric car.
The key, Smalley says, is that such a battery demands a substance whose molecules do not change shape when they accept or give up electrons. “Fullerenes with metals in them have an interesting advantage,” he adds. “If there’s ever a molecule that won’t change its geometry when trading electrons, it would be this spherical one.” That’s because buckyballs are so symmetrical that they would strongly resist deformation.
Buckyballs in bulk offer further prospects. Smalley sees them as raw material for a new type of tailor-made catalyst, which might outdo other catalysts in assisting the reactions that are the heart of the petrochemical and pharmaceutical industries. “You could make a structure with pores and cavities in it of controlled size,” by adroitly joining the proper fullerene molecules, Smalley says. These molecules would have modifications added beforehand, ensuring that the resulting lacy and porous molecular assembly indeed would offer the right catalytic action. Controlling the size of the cavities would control the size of molecules that could pass through and significantly influence the catalytic process.
There is even the prospect that the round buckyball molecules could serve as the ultimate ball bearings. You might deposit a layer of buckyballs on a surface of metal parts; or you dissolve the molecules in motor oil. “Perhaps it would be the best additive,” Smalley says.
At IBM’s Almaden Research Center in San Jose, a group led by Don Bethune has already shown that buckyball molecules freely rotate, even when locked in place within a crystal. If buckyballs prove to be a good lubricant, they would share this property with diamond surfaces and with graphite, which has long been in use for this purpose.
In a surprising finding earlier this month, scientists reported that buckyballs may be good superconductors. Superconductors are materials that allow electricity to flow with virtually no energy lost to resistance and wasted as heat.
Reporting in the British journal Nature, Arthur Hebard and his colleagues from AT&T; Bell Laboratories in Murray Hill, N.J., said they found when gaps in buckyball material were filled with potassium atoms, the material became a superconductor.
“I never heard of anyone predicting buckyballs would do this. It really is completely astonishing to everybody,” said Whetten, a professor of physical chemistry at UCLA.
“Who knows where this will lead. The material is simple, easy to prepare, lightweight and both carbon and potassium are cheap,” said Whetten, who has been able to reproduce the AT&T; results in his laboratory.
However, Whetten also sees buckyballs by contrast as a reason for worry. He believes they may be present naturally in smoke from cigarettes and other sources. This would mean that “these molecules are being produced all the time in the environment, at small enough levels that they haven’t been noticed yet.” They then might produce singlet oxygen within the air itself, which could damage lung cells.
Whatever promise or problems are held by these possibilities, researchers will certainly not lack for the buckyballs themselves. Already two start-up companies--Texas Fullerene Co. in Houston and MER Corp. in Tucson--are producing quantities for use in these studies. Dieterich notes that the process is simple enough that high school students have carried it out in his lab.
Donald Huffman, inventor of the process, notes that the amounts produced can be “anything you want. If there turns out to be a need for tons, it can easily be scaled up to tons.” And Smalley adds that “our guess is, it will be about the cost of aluminum.” That would be $5 to $10 per pound of buckyballs, if industrial-scale production should emerge.
INSIDE THE BUCKYBALL
Drawing shows the buckyball’s crystal structure with the ball-like cluster at right. The unlabeled circles represent carbon atoms. The osmium, oxygen and nitrogen atoms labeled at left formed a “tail” that enabled scientists to produce a clear x-ray picture of a stable buckyball.
