The following is the edited text of "A Winning Essay"
The Chemistry Hall of Fame is a registered trade mark of York University.
C60 - Carbon's 'Missing Link'
by Lindsay Taylor, Waterloo Collegiate Institute, Waterloo, Ontario
What started as a "hollow graphite balloon" in 1966, progressed to a ball of paper and tape in 1985, had heralded the development of three-dimensional fullerene chemistry (and biochemistry) and associated cluster/microcluster research by 1990. Its basis: The C60 "buckyball", named for R. Buckminster Fuller, developer of architecture's 'geodesic' dome. 4
Richard Smalley and Robert Curl of Rice University, and Harry Kroto of the University of Sussex in England, have shared the credit for the discovery, but it was very much a collaboration. 5
First noted in common 'soot', and now speculated to be part of the cosmic molecular streamers stretching to the centre of the galaxy6, C60 was only produced mechanically in 1990 by laser-vaporizing graphite in a pulsed jet of helium.7 Recent research has focused upon creating sufficient quantities to allow its many theoretical uses to be explored.
The molecule is edgeless, chargeless and unbound, spinning freely. Inert and stable, in crystal form as soft as graphite, but compressed to less than 70% of its volume, C60 becomes harder than diamond. Capable of 'caging' very reactive elements to make them manageable, it possesses a unique affinity for the development of exohedral and endohedral complexes. 8
The pharmaceutical industry is exploiting its inert state and its ability to bond with an as yet indeterminate number of other elements, molecules and chains. It is in use in AIDS research and chemotherapy and serves as a delivery vehicle for chemical treatments and diagnostic modes such as radioactive tracers. 9
Application to lubricants are under study by Exxon and others. Fluorine bound to the ball's exterior has been found to enhance the natural ability of its round shape, by giving it properties similar to 'Teflon', but possibly better for the combination. 10
At IBM and AT&T Bell Laboratories, investigation of electronic characteristics and applications of buckyballs that function as insulator, conductor, semi-conductor and superconductor are underway. 11
Films Of C60 on a substrate have applications to optical memories and image processing. Some even see these as the forerunners of electronic devices constructed on a molecular scale. Structured on a carbon-based molecule, such devices could become the long-envisioned link between solid-state and biological systems. 12
Speculation abounds as to 'nano-technology' applications - The Most Beautiful Molecule, Aldersey-Williams
Industrial catalysis and pollution control are being studied with respect to the ability of the C60 active sites to control desired and undesirable reactions with other chemicals. 13
The interdisciplinary research into fullerenes is as yet in its infancy, but sufficient knowledge now exists to suggest that it has great relevance to fields as diverse as materials science, medicine and pharmaceuticals, electronics and astrophysics. Its discovery shocked the chemical world - suddenly there were not two but three basic forms of network solids - and the surprises continue every day. The fact that it has provoked thought in such a variety of applications suggests its induction into the Chemistry Hall of fame is only the beginning of an illustrious story.
References and Notes
- David Jones, in his article "Adriane", published in New Scientist, Nov. 3, 1966 seemed to be indulging in prophecy (but not real science) when he described in great detail what was not to be discovered for another 20 years: "There is a curious discontinuity between the densities of gases at around 0.001 relative to water and liquids and solids from 0.5 to 25 or so; this week Daedalus has been contemplating ways of bridging this gap and has conceived the hollow molecule, a closed spherical shell of flat sheets of benzene-hexagons; He proposes the modify the high temperature graphite process... to warp them, reasoning that the curvature thus produced will be transmitted throughout the sheet to its growing edges so that it will ultimately close on itself.. These low-density substances would constitute a vague fifth state of matter, for such big molecules... could hardly evaporate but would interact so weakly that their few points of contact would not be solid or even liquid... Such fascinating new materials would have a host of uses, in novel shock-absorbers, thermometers, barometers, and so on, and possibly in gas bearings where the rolling contact of the spherical molecules would lower friction even further... [If] synthesized in a normal atmosphere, they would be full of gas and resilient like little footballs: he is now seeking ways of incorporating 'windows' into their structure so that they can absorb or exchange internal molecules , so as to produce a range of super molecular-sieves capable of entrapping hundreds of times their own weight of such small molecules as can enter the windows."
- In his text, The Perfect Symmetry. (Oxford University Press, N.Y.1994) Jim Baggott describes the brainstorming that went on over dinner between Harry Kroto, Rick Smalley and Bob Curl that lead to Smalley's construction of a crude paper and tape model. Smalley envisioned a geodesic dome of the type R. Buckminster Fuller created and immortalized in architecture, and Curl and Kroto added the sticky labels representing the double bonds to check to see if the carbon bonding requirements could be met for every one of the molecules' 60 atoms. It did, and they had their first view of the "buckyball".
- 1990 was the year when a variety of individual events in the United States, England and Germany saw the first mechanical production in any useable quantity Of C60 molecules. From these samples, the scientists were able to work back to test their hypotheses and prove the existence and properties of the molecule that had until then been speculated upon from theoretical models and spectroscopic analyses.
- The inspiration behind the naming of the "Buckminsterfullerene", the "buckyball" as it became affectionately known to its discoverers, or the "fullerene" in scientific parlance, is described in amusing detail in Jim Baggott's Perfect Symmetry: The Accidental Discovery of the Buckminsterfullerene, and in Hugh Aldersey-Williams' text The Most Beautiful Molecule: The Discovery of the Buckvball.
- The Baggott and Aldersey-Williams texts describe the various contributions of such persons as Smalley, Kroto, and Curl as well as a cast of hundreds in terms of related researchers and research assistants including but not limited to: Kosta Fostiropoulos, Patrick Fowler, Jim Heath, and Wolfgang Kratschmer. Credit is given to the inspiration of R.Buckminster Fuller, and even the 18th century mathematician Leonhard Euler, who theorized on a spherical model and calculated that any such object must have precisely 12 pentagons in order to close into a spheroid, although the number of hexagons could vary widely. This credit is acknowledged by Curl and Smiley in their paper "Fullerenes" published in Scientific American, October 1991.
- The theory that soot-like particles under distinguishable circumstances would turn in on themselves and create C60 soccer ball-shaped molecules was estimated to occur with an almost unimaginable infrequency. According to Jim Baggott ( pg 96), some took comfort in this idea, for to believe that a beautifully ordered molecular structure is created out of the chaos of the universe with any more frequency, seemed to go against the grain of the second law of thermodynamics which demands that in spontaneous change, order tends to decrease. But the eventual mechanical creation Of C60 suggests that in theory, huge carbon-rich red giant stars are pumping out vast quantities of smoke and soot into the interstellar medium. And this is supported in the earliest stages of C60 research when the likes of Kroto and Charles Townes of the University of California, Berkeley, themselves microwave spectroscopists by training, found readings suggestive of the existence of the presence of ammonia and like molecules in the inner reaches of the galaxy.
- The apparatus is described as "A-P2", being simply the second such apparatus developed by Smalley while at Rice University. Technically it is a "laser-supersonic cluster beam apparatus" and the equipment and process is described in the works of Aldersey-Williams and Baggott.
- In The Most Beautiful Molecule, Aldersey-Williams wrote: "The fear that the symmetrical molecules would lose too much of their stability if disrupted by an added chemical groups had been shown to be unfounded. The aim now is to be able to add chemical groups in a controlled manner, and in just those places and numbers desired. (The situation is superficially parallel with the substitution chemistry of the benzene ring, where many thousands of molecules can be made, with myriad uses, by substituting chemical groups in appropriate permutations on the six carbon sites of the ring... With sixty bonding locations on the surface of the buckminsterfullerene, the synthetic permutations are virtually endless.)." I would also refer to such recent practical studies as "Synthesis of a Fullerene Derivative for the Inhibition of HIV Enzymes" published in the Journal of the American Chemical Society, 1993,115, 6510-6512 by Sijbesma, Srdanov et al. of the University of California at Berkeley. The mechanical creation of C60 and other Cn fullerene molecules is ongoing as part of a wide range of experiments into the application to pharmaceuticals. It was found, for example, to be an ideal vehicle for the attachment of an amino acid chain that could then be placed into a host infected with AIDS. The amino acid would dock into the gp-120 active site of the AIDS virus and inhibit its ability to attach to the receptor sites on the human CD4 cells, where AIDS does its damage. The concept worked, but is temporarily shelved as it is less effective than some present alternatives, most notably AZT (although AZT is effective in suppressing only acutely infected cells). Suggested reading is Rudy Baum's "Fullerene Bioactivity: C60 derivative inhibits AIDS viruses", Chemical and Engineering News, August 2, 1993. Research papers abound on the topic as it relates to medicine and pharmaceuticals.
- Cages of carbon by Tim Fowler appears in the 'Chemistry Watch' section of Discover, The World of Science magazine, September 1993, pg.32. In medicine and industrial applications, he notes that such elements as helium that can be detected in minute quantities, can be used as chemical tracers in impregnated buckyballs. The applications range from therapeutic to diagnostic purposes in medicine, to pollution tracking. Elements such as lanthanum dicarbide which reacts very strongly with water vapour and oxygen and rapidly degrades in air, have been successfully protected in a fullerene 'cage' for more than six months according to researchers at SRI International, Menlo Park, California. More 'caged' applications are expected to be developed. Aldersey-Williams suggests in The Most Beautiful Molecule that the exohedral chemistry activated by the opening of the surface double bonds is already coming to resemble a novel extension of the chemistry of the unsaturated organic compounds, the alkenes... [and] The endohedral fullerenes are more in a class of their own. It is possible to envision them as a kind of periodic table, with each element capable of being inserted into the cage appearing as if through a carbon mist." Pages 264 through 267 of his text discusses the similarities and differences in the "carbon periodic table" so formed, and Mendeleev's.
- It is suggested that the free-spinning spherical shape of the buckyball naturally resembles that of a miniature ball bearing. Added to that is the lack of attraction between the balls in close association. Teflon, the low-friction coating substance, is a carbon chain with fluorine atoms attached. It is an area of lubricant research to see if the carbon buckyball coated with fluorine in a similar fashion would not presumably roll past one another better than ever.
- When C60 is 'doped' with potassium to form K3C60 and the mix is cooled to below 18K, it becomes a superconductor. If greater amounts of potassium are used in the doping reaction, the resultant crystal is an insulator. And the ability to absorb and subsequently give up electrons might even make fullerenes the basis of a new class of battery, lighter and more efficient than lead-acid batteries. Bell Laboratories and NEC Corporation are looking at these areas, although the temperature requirements are an obstacle. "Nevertheless", according to Aldersey-Williams, " the fullerenes remain among the most favoured contenders for practical superconductivity."
- An interesting discussion of 'nanotechnology' is found in Aldersey-Williams' text The Most Beautiful Molecule (pp. 282-285) where he in turn draws from the book Engines of Creation: The Coming Era of Nanotechnology, by Eric Drexler. He states that where Drexler is "wisely vague on what materials will comprise the new nanomachines and nanocomputers ... implicit in every mention of 'nanomachines of tougher stuff than protein' or the ability 'to bond together virtually in every stable pattern' is the candidacy of the fullerenes and these other carbon networks."
- Speaking of the emerging study of "microclusters" in the earliest days of research and before the buckyball - a form of microcluster - came to prominence, Michael Duncan and Dennis Rouvray (Microclusters", Scientific American, Dec. 1989, pages 110-115) described industrial catalysis as a "promising application" of the unique surface chemistry of clusters. Catalysis begins when the surface of the catalyst 'absorbs' molecules, allows the molecules to drift to active sites, where bonds are broken and reformed. The new molecule so formed is the 'desorbed', and the catalyst is available to repeat the process. Some of Richard Smalley's research in the early 1980's was in this area, and the work continued through the University of California, Los Angeles and the University of Utah among others. Clusters were ideal for the study of active sites and their unfilled bonding capacity makes them adsorb readily and their small size limits the number of possible adsorption geometries This feature "also makes them likely sources of highly specific catalysts, which do what they are intended to do and no more." That specificity is highly prized in industry, because many catalysts speed undesired reactions just as effectively as they speed desired ones.