As with many important scientific discoveries, buckyball was discovered by accident. In 1985, the American chemist R. E. Smalley at Rice University, the British chemist H. F. Kroto at Sussex, and graduate students working under their direction were studying the nature of interstellar matter.
They wanted to know what forms of carbon-containing materials can be found between the stars. The overall strategy of the research was to compare spectroscopic readings from unidentified matter in interstellar space with those obtained from well-characterized materials in the laboratory. If a match is found, then one can infer the nature of the interstellar matter. This strategy reveals a fundamental principle of the rules describing matter: they apply equally throughout the universe. Buckyball is the roundest and most symmetrical large molecule known to man. Buckministerfullerine continues to astonish with one amazing property after another.
Named after American architect R. Buck minister Fuller who designed a geodesic dome with the same fundamental symmetry, C 60 is the third major form of pure carbon; graphite and diamond are the other two. When buckyball was discovered, Kroto and his coworkers already knew that long chains of carbons were present in space. This knowledge was based on the readings obtained from a radio telescope. Every molecule exhibits a characteristic reading on this telescope that is like a fingerprint. This fingerprint can be compared to the fingerprint given by known molecules on earth, hence, the molecules in interstellar space are characterized.
The nature of spectroscopic analyses used to characterize interstellar matter is a topic that is too involved for further discussion at this point. Instead, we turn our attention to the methods used to discover buckyball. Smalley's apparatus was designed to generate long chain carbon molecules so that their spectroscopic fingerprints could be measured. In the Smalley apparatus a laser is aimed at a rotating graphite disk in a helium-filled vacuum chamber. This apparatus uses the ability of lasers to deliver short, high energy bursts of energy in the form of light.
The rapid, intense heating of the graphite surface by the laser enables many of the C-C bonds in the graphite to rupture. As a result, carbon atoms and small clusters of carbon atoms sputter from the graphite surface. Thus, the energy of the light produced in the laser is used to break the bonds between atoms in graphite, a process that involves the conversion of light energy to chemical energy. The high energy C atoms and small clusters of carbon atoms cool and collide in the He atmosphere yielding new bonding arrangements of C atoms. These new materials can be characterized by different instruments.
The two instruments that played a key role in the discovery of buckyball are mass spectrometers and nuclear magnetic resonance spectrometers. On the basis of the information provided by mass spectrometry, Kroto, Smalley, and coworkers were faced with the problem of rationalizing the unusual stability of 60 carbon atoms bound together to make a molecule of buckyball. The fundamental issue concerned how to construct a molecular structure that satisfied normal bonding (four bonds per carbon atom) and comprised exactly 60 atoms of C. With a great leap of both insight and faith, as well as considerable influence from the geodesic dome structures designed by Buckminster Fuller, these collaborators proposed that C 60 adopts an arrangement of carbon atoms that is similar to the stitching on a soccer ball. one traces the C-C bonding framework.
Each carbon lies at the vertex of fused 5- and 6-membered rings But why should C 60 be so stable The alternation of single and double bonds in a molecule has been found to correlate with unexpected stability in molecules closely related to C 60. By stability we mean that the forces, or bonds, holding the carbon atoms close together are stronger than one might have expected from comparison with simpler, related materials. Consider the example of C 6 H 6. Various experimental measurements indicate that benzene (C 6 H 6) contains six carbon atoms arranged at the vertices of a hexagon. Attached to each carbon atom by a single bond is a hydrogen atom. One can satisfy the bonding rules for carbon and hydrogen by (1) joining each hydrogen to a carbon atom with a single bond and (2) arranging bonds between the carbon atoms in an alternating single-double-single pattern as shown in the figure.
Two arrangements of C-C double bonds in benzene are possible; the two structures differ only in the positioning of the double and single bonds. Why a soccer ball If one traces the stitching on a soccer ball, one finds exactly 60 vertices, or points where three lines of stitching intersect. A soccer ball has both 6-membered (hexagonal) and 5-membered (pentagonal) patches. These are sewn together to make a round ball. Taken in by the beautiful symmetry of such structures, Kroto and Smalley conjectured that if 5-membered and 6-membered rings of carbon were placed together in the same pattern then a round molecule containing 60 carbon atoms would result. In another area of work with buckyball, a derivative of C 60 was shown to inhibit HIV-1 and HIV-2, the human immunodeficiency viruses that cause AIDS.
Researchers at the Univeristy of California, San Francisco, noticed that buckyball fit perfectly into the active site of HIV proteases. (The active site is where reactions occur. ) A water-soluble derivative of C 60 was made by Fred Wud l and co-workers at the University of California, Santa Barbara, and this compound was indeed shown to disarm the HIV virus and block HIV protease from cutting proteins. The infected cells themselves, however, were not damaged. At Emory University, inhibition of HIV's ability to infect cells was also shown using a water-soluble derivative of buckyball. Unfortunately, the potency of the buckyball analog is low when compared to AZT and other HIV enzyme-inhibiting drugs.
To be useful, the buckyball.