MALCOLM W. BROWNE - July 10, 1992
Carbon-based molecules shaped like soccer balls have fascinated chemists since the first one was synthesized seven years ago. Now for the first time these molecules, fullerenes, have been found in nature, lodged in rock that seems to date from the dawn of life on our planet.
The discovery, reported in today's issue of the journal Science, has mystified scientists, who cannot explain the origin of the natural fullerene molecules or even of the enigmatic mineral in which they were found.
The discovery of fullerenes created a new dimension of chemistry and a family of molecules as fascinating to scientists as Tinker Toy sets are to children. Fullerenes might even turn out to have commercial uses in areas like rocket fuel to pharmaceuticals, a prospect chemists cite when asking for money for pure research.
Rare, Ancient Mineral
The accidental discovery of natural fullerenes was made by geochemists at Arizona State University at Tempe while studying a coal-like mineral taken from rock sediments apparently formed during the Precambrian era, more than 600 million years ago. The rare black mineral, 99 percent carbon, was noticed by scientists more than a century ago in seams of very old rock near the town of Shun'ga in Russian Karelia some about miles northeast of St. Petersburg. The scientists named it shungite, after the town.
The Arizona State investigators, headed by Dr. Peter R. Buseck, recently stumbled upon fullerenes in a sample of shungite they were examining with a High-Resolution Transmission Electron Microscope, an instrument so powerful it can record images of individual molecules.
Earlier, Dr. Buseck said in an interview that one of his students, Dr. Wang Su, had recorded an image of synthetic fullerene molecules that showed them arrayed in neatly packed rows. Then last year a Russian scientist, Dr. Semeon J. Tsirpursky, joined the group and continued a study he had begun in the Soviet Union on the mineral shungite. When he saw Dr. Wang's electron micrographs of synthetic fullerenes he was struck by their similarity to images he had made of the carbon molecules in shungite.
Subsequent analyses have confirmed the presence of fullerenes in the Precambrian mineral. A sample was sent to Oak Ridge National Laboratory, where Dr. Robert Hettich subjected it to analysis by mass spectrometer, an instrument that sorts out molecules according to their masses and electric charges. Dr. Hettich found that the shungite contained the two most common synthesized fullerenes, assembled respectively from 60 and 70 carbon atoms.
Very high temperatures and carefully controlled gas pressures are needed to make fullerenes in the laboratory. The right conditions are not common outside the laboratory.
Perhaps an even greater mystery is the origin of shungite itself. Two Russian scientists, I. V. Volkova and M. V. Bogdanova, reported finding evidence of "woody structure" in shungite, implying that shungite, like coal, formed from fossilized plants. The trouble with this idea is that none of the plants that formed conventional coal deposits existed so early in Earth's history as the Precambrian era, when life was limited to primitive single-cell organisms.
The rock in which the the shungite is embedded apparently belongs to strata corresponding to Precambrian age, and it is difficult to explain how a younger carbon mineral could become embedded within its fissures.
Dr. Buseck said shungite was so rare that "even the Smithsonian Institution doesn't have any of the stuff."
Aside from their scientific interest, fullerenes may have important uses.
When certain metal atoms are attached to fullerene molecules, they conduct electricity without resistance at relatively high temperatures, suggesting that fullerene compounds might one day be useful superconductors.
In another application, the National Aeronautics and Space Administration believes fullerenes might be used as propellants in ion rockets that might one day power interstellar missions.
And scientists in France and the United States have discovered that fullerenes offer advantages over ordinary carbon in making synthetic industrial diamonds; under high pressure, the 60-carbon-atom fullerene can be compressed into diamond at room temperature, avoiding the high temperatures normally required to transmute graphite to diamond.
Fullerenes are also under study as materials for building optical communications switches, lubricants, catalysts and molecular "pills" in which minute amounts of drugs might be delivered to specific parts of the body.
Dr. Harold W. Kroto of the University of Sussex, England, and Dr. Richard E. Smalley of Rice University in Houston synthesized the first fullerenes in 1985.
Fullerenes, nicknamed "buckeyballs," are named for the late Buckminster Fuller, an engineer who frequently designed architectural structures based on geodesic domes.
Their molecular counterparts, the fullerenes, have given rise to a rich new field of chemistry. Inside the molecule, each carbon atom can serve not only in holding the structure together but as an attachment point for an external atom or molecule. The potential chemical combinations made possible by fullerenes are practically endless.