Second Wave Of `Buckyball' Researchers Kicks Off Efforts

Two years ago, the 60-carbon, soccer ball-shaped buckminsterfullerene was just a curiosity for Larry Lewis, a staff chemist at the General Electric Co. Corporate Research & Development center in Schenectady, N.Y. At the time, his interest in the recently identified molecule was restricted to "what if" questions inspired by perusing numerous journal articles about it. He couldn't do any lab work with it, though, Lewis says, because "there wasn't enough of the stuff to do chemistry with." But all of that changed last September, when scientists succeeded in making gram quantities of the material. Now, just about any bench scientist can join the original "buckyball" pioneers in exploring the properties of C60 in his or her own lab. It was late on an August evening six years ago that Rice University professor Richard Smalley sat in his kitchen, cutting out shapes from a legal pad and taping them together. He was trying to come up with a model having 60 vertices to represent the 60-carbon molecule which he and his collaborators generated in the lab by laser-vaporizing carbon in helium gas. Chemist Harold Kroto was one of these collaborators. He had come to Rice from the University of Sussex in England to use the Houston school's laser technique, with which he hoped to be able to generate carbon chains he thought might be components of interstellar dust. A year earlier, in 1984, Eric Rohlfing, Donald Cox, and Andrew Kaldor at the Exxon Research and Engineering Co., then in Annandale, N.J., had done a similar experiment and noted that the resulting carbon chains always had an even number of atoms (J Chem. Phys., 81:3322-3331, 1984). Kroto, Smalley, and the other members of Smalley's research team at Rice found that the most abundant chains had 60 carbon atoms. Had the team discovered a pure carbon other than graphite or diamond? That night in August they all went home to puzzle out the shape of this new molecule. Graduate student James Heath and his wife tackled the geometric problem by connecting the chewy candies called Gummy Bears with toothpicks. Smalley tried at first to generate a C60 figure on his personal computer, but soon abandoned that for the easier-to-use scissors, paper, and tape approach. But his organic origami didn't get very far when he used only hexagons. Then he remembered Kroto mentioning a 30-cornered dome he'd built for his kids, which had a few pentagons among the hexagons. When Smalley began surrounding paper pentagons with hexagons, a form rapidly emerged. First it looked like a salad bowl. When a hemisphere with exactly 30 vertices appeared, he knew he'd hit pay dirt. Quickly doubling the hemisphere, he saw an exquisitely symmetrical sphere. Viewing it as a mathematician might, he recognized a truncated icosahedron. Had Smalley been a soccer aficionado, he would have instantly recognized the form as that of a soccer ball. At a meeting the next day in Smalley's office, C60 was officially named, and today these carbon "cages" are known as fullerenes after architect R. Buckminster Fuller. The smallest has 24 carbons, and Kroto predicts they can be as large as C240 and C540. C60 is often found with the rugby ball-shaped C70. Higher fullerenes of 76, 84, 90, and 94 carbons have been isolated by chemists Francois Diederich at the University of California, Los Angeles, and Frederick Wudl at UC-Santa Barbara. --R.L. Before the molecule was isolated, chemists believed that pure carbon came either in hexagonal-layered, chicken wire-like sheets of graphite or in pyramidal or tetrahedral crystals of diamonds. But while trying to replicate the short-carbon chains found in interstellar dust by simulating the enormous heat found in giant red stars, chemists kept observing elegant clusters of 60-carbon atoms. After much model-building, the chemists observed that these clusters were shaped like the geodesic dome invented by architect and engineer R. Buckminster Fuller. Although Lewis's work on metal-catalyzed reactions is unrelated to the chemistry of these huge, hollow carbon balls, the spectacular size and symmetry of C60 proved an irresistible lure. Today, Lewis, an inorganic chemist, is experimenting with the buckyball because he believes it could have attachment points for chemical reactions. "You could have one molecule with lots of metals poking out and interacting with one another, possibly catalyzing reactions," he speculates. The New Wave Lewis is one of thousands of new-wave buckyball researchers--the "dabblers" beginning to experiment with the trendy molecule. For $100, scientists in industry, academia, and government can buy 50 milligrams of the stuff; and in terms of research opportunities, these balls may be for 21st-century chemists what benzene was for their 20th-century counterparts. By elucidating the structure of benzene, chemists learned how to make compounds as varied as aspirin and plastic. Now, given the frenetic activity of these researchers, experts already are predicting that the first applications of the buckyball are on their way. The excitement generated by experimenting with C60 has been chronicled in "The Almost (But Never Quite) Complete Buckminsterfullerene Bibliography," a large database compiled by Richard Smalley, a professor in the departments of chemistry and physics at Rice University in Houston. Smalley, who will send this database to interested researchers, led the team that deduced the structure of C60 (Nature, 318:163-4, 1985). His collaborators were Robert Curl, a professor of chemistry from Rice; their graduate students, James Heath and Sean O'Brien; and visiting University of Sussex (Brighton, England) chemist Harold Kroto. Smalley's database, which is updated daily, begins with the base 60 number system used by the Babylonians some 3,500 years ago, and ends with articles currently in press. It lists one paper on C60 in 1984 and four in 1985, but after the structure was suggested in 1985, publications rose to two or three dozen a year. "Then interest began to die off, because no one could make the stuff. But since our discovery of less than a year ago, there have been more than 200 papers published," says Donald Huffman, a professor of physics at the University of Arizona, Tucson. Huffman and graduate student Lowell Lamb, along with Wolfgang Kratschmer and Konstantin Fostiropoulos of the Max Planck Institute for Nuclear Physics in Heidelberg, Germany, published the Sept. 27, 1990, paper (Nature, 347:354-58, 1990) spelling out how to synthesize large quantities of C60 (see "Hot Papers," page 15). According to the Institute for Scientific Information in Philadelphia, this paper is the most cited in chemistry in the last two years. C60 is also the topic of six of the top seven cited papers in chemistry in the same period. "If C60 was a hot topic of 1985 to 1990, it is super now," says Huffman. By Smalley's count, there were 87 C60 papers published in the first quarter of 1991, and 89 that he knows about for the second quarter. Meeting attendance is another measure of C60 fervor. More than 500 attendees stayed past midnight at a fullerene symposium during the Materials Research Society meeting in Boston last December. The scene was similar at the March 1991 American Physical Society meeting in Cincinnati and a month later at the American Chemical Society meeting in Atlanta. The August 2 and 3 "Workshop on Fullerites and Solid State Derivatives" in Philadelphia was jammed; at the Electrochemical Society meeting in Phoenix, scheduled for October 13-18, a "Symposium on Fullerenes: Chemistry, Physics and New Directions" is also expected to be standing room only. The buckminsterfullerene saga reveals science in its best light; its themes include careful experimentation spawning important, serendipitous findings and cooperation among semi- competing researchers. Discoveries have been fueled by a curious mix of high-tech and down-home approaches. What the scientists eventually determined was that C60 is arranged in 12 pentagons and 20 hexagons. "What makes 60 special is that the strain of the curve is uniformly distributed," says Smalley. This explains why C60 is so stable, and why a geodesic dome encloses a maximum of space in a minimum of material. The molecular symmetry that the Rice University group had inferred from a hand-constructed paper icosahedron (see accompanying story) was confirmed in 1990 by visiting researcher Kroto and his colleagues at the University of Sussex. Their nuclear magnetic resonance work revealed an identical chemical environment for each carbon atom in the molecule. Restaurants succeed because people would rather buy the food than prepare and cook it themselves. The situation may be the same with fullerenes--and that's what a handful of companies are banking on. "You can get nice, pure stuff if you make it yourself, but that route is not without problems. It takes about a week to get 250 milligrams of pure material. So the prices are not out of line at all," says Christopher Foote, a chemist at the University of California, Los Angeles. Price ranges offered by the different companies reflect the newness and rapid pace of fullerene research, with some companies charging different prices for academic and industrial buyers, and offering fullerenes in various degrees of purity. For example, Texas Fullerenes Corp. of Houston--a startup waiting for a license under any patent issued to Richard Smalley, the Rice University professor who deduced the structure of C60--offers impure "C60-rich soot" at $10 per gram for universities and $20 per gram for nonacademic users. The company charges $500 per gram for a "mixed fullerene extract" (including C60 and larger carbon cages) and pure C60 for an unspecified price. Current prices and the fact that researchers still must purify the C60 from the soot and separate the C60 and the C70 in the purified product has kept some investigators away from the commercial products. But that may change. "In another few months, with competition [between companies] up, prices will come down, and then it will not be worthwhile making your own," says Frederick Wudl of the University of California, Santa Barbara. With eye-catching, direct-mail postcards--illustrated with soccer balls--sent to 25,000 scientists, Strem Chemicals Inc. of Newburyport, Mass., is gearing up for fullerene demand. Strem markets the chemical for manufacturer Materials and Electrochemical Research (MER) Corp., based in Tucson, Ariz. MER licensed the production process from Research Corporation Technologies of Tucson, a company that has applied for the patent for the Huffman/Kratschmer technique. Ed Malone, Strem Chemicals' director of marketing, says that most buckyball purchasers buy the purified mixture of C60/C70 in 50-milligram amounts. --R.L. Although few doubted that C60 had a soccer ball configuration, a mass spectrograph and the paper ball are only indirect evidence. Plus, the small amounts of C60 weren't enough for researchers to sink their teeth into. Finding a way to make it in macroscopic amounts was the next challenge. That breakthrough came in 1990, when Huffman, Lamb, Kratschmer, and Fostiropoulos passed an arc of electrical discharge between two carbon rod electrodes in a helium gas and collected soot that was 15 percent C60 and C70. Although the group had produced C60 in 1983, they didn't identify it until Smalley's group's results were published in 1985. "So in 1990, we found a way to extract C60 out of the soot we had been making since 1983," Huffman says. A group from the Exxon Research and Engineering Co., then in Annandale, N.J., had also unknowingly produced C60 prior to 1985. Using the Huffman-Kratschmer technique, a researcher could produce 0.01 gram of C60 a day. Smalley's group rapidly improved the yield to 10 to 20 grams, and then chemistry professor Robert Whetten at the University of California, Los Angeles, improved it further. Scaling up buckyball production allowed the X-ray crystal structure of C60 derivatives to be determined, which confirmed the soccer ball structure, and it finally provided enough material for a virtual avalanche of experiments (see story on page 16). Chapter 2 During what Smalley has dubbed "Chapter 2 of this adventure," the discoveries came rolling in. Arthur Hebard, Matthew Rosseinsky, and their group at AT&T Bell Laboratories in Murray Hill, N.J., found that thin films of C60 doped with potassium or rubidium become superconducting at 18 degrees and 28 degrees Kelvin, respectively--the highest such superconducting temperatures for an organic material (Nature, 350:600-601, 1991). Adding the impurity apparently lowers the energy needed to move electrons in a way that lowers electrical resistance and thus offers the potential for more efficient electrical devices. On June 18, 1991, the Wall Street Journal reported that scientists from NEC Corp. of Tokyo said they made a buckyball with cesium and rubidium that became superconducting at 33 degrees Kelvin. Although the NEC ball is better than the Bell Labs ball, it still functions at temperatures too far below the temperature of liquid nitrogen, at which the most promising superconductors operate. Buckyballs also behave like a molecular Velcro, sopping up electrons in binding atoms. Wudl's group attached the short organic compound ethylene diamine by its nitrogen electrons to C60, causing the tail-like structures to poke out of the sphere, creating a "hairyball." When Smalley "doped" C60 with the impurity boron nitride, "dopeyballs" were born. Scanning tunneling micrographs of C60, resembling egg cartons, appeared in back-to-back Nature papers, one by Huffman, Kratschmer, and collaborators at the University of Missouri in Columbia and the other by R.J. Wilson's group at IBM's Almaden Research Center in San Jose, Calif. (348:621-624, 1990). Mysteries Explained Of great interest is how and where buckyballs form in nature. The details of C60's genesis emerged as Smalley's paper-and-tape creation grew to accommodate the 60 carbon atoms. The great balls of carbon form as hexagonal sheets curl when pentagons get incorporated into the structure. But if buckyballs form in such a simple manner, then why aren't we tripping over them in nature? We simply haven't looked in the right places, says Smalley. Plus, various conditions are necessary for fullerene formation: no hydrogen, which rapidly ties up the dangling bonds in a prebuckyball graphitic sheet; no oxygen; and intense heat. Fullerenes dominate the many carbon-based compounds formed when a flame reaches 2,200 degrees to 2,600 degrees C. Another habitat for C60, similar to conditions in a sooting flame, may be the outer atmosphere of carbon-rich red giant stars. It was the hypothesis that fullerenes might account for unidentified spectral lines in light from space that led Kroto to the Rice University lab in 1985. C60 molecules adrift in space, thriving amid high temperatures, and inert gases pulling on atoms may have seeded dust particles that accreted into larger heavenly bodies as the universe was born. What's Next Synthesizing new compounds based on C60 is likely to be the hottest new area of fullerene research. Says Arizona's Huffman, "Whenever you put a new atom in a C60 cage, or when you attach an atom to the outside, it is a new molecule. There will be a proliferation of molecules and solids based on this material, and a lot of work on defining their properties." Smalley envisions an entire new chemistry, "a new periodic table encapsulated in an M&M coating," by sticking each element inside a buckyball. What will be the first commercializable fullerenes? A superconducting wire, a photoconductor to make solar cells, and a new lubricant, says Smalley. The molecule's potential as a lubricant is based on its unusual ability to be greatly compressed, yet return rapidly to its normal state when pressure is released. Buckyballs may also provide a new route to diamond synthesis. But those at the forefront of this fledgling field fear that the first application will sound the death knell for the camaraderie that has made unraveling the mystery of buckminsterfullerene so much fun. "So far we've all been doing different things on the same molecule," says Wudl. "But pretty soon, a lot of people will be doing the same thing, and then there will be some animosity." In an era when biotech companies regularly battle over rights to variations on the same molecular theme, concern exists over an end to the buckyball party. Investigators contrast C60 research's openness to the secrecy and intense competition that characterized the superconductivity race a few years ago. And Huffman mentions a recent scientific fiasco, characterized by deception and fraudulent claims, compared to which fullerene research comes up smelling like the proverbial rose: "Cold fusion was a much more exciting discovery, but. . . hardly anybody could reproduce it. Our work is in sharp contrast. We wrote it up so that everyone could do it--and that's what science is all about." Ricki Lewis teaches biology at the State University of New York, Albany, and is the author of Life, a college biology text (Dubuque, Iowa, William C. Brown Publishing, 1991). Aldrich Chemical Co. P.O. Box 355 Milwaukee, Wis. 53201 Phone: (800) 558-9160 25 mg for $60, 100 mg for $180 Materials and Electro-chemical Research Corp. 7960 S. Kolb Rd. Tucson, Ariz. 85706 Phone: (602) 574-1980 1 g soot $20; 2-5 g $18/g; 6-10 g $16/g; 11-20 g $15/g; 21-50 g $12/g; 51-100g $10/g buckminsterfullerene 100 mg (C60/C70) $100; 1g $450; 2-5 g $350/g Research Materials Inc. 1667 Cole Blvd. Building 19 Suite 400 Golden, Colo. 80401 Phone: (303) 238-9369 C60/C70 mixture 100 mg for $350 Strem Chemicals Inc. 7 Mulliken Way Newburyport, Mass. 01950 Phone: (508) 465-3104 1 g carbon soot (yield 100- 200 mg C60/C70) $80; 5 g for $360; 25 g for $1,500 buckminsterfullerene C60/C70 (2-12% C70) 50 mg for $100; 250 mg for $400; 1 g for $1,250 Texas Fullerenes Corp. 2415 Shakespeare St., Suite 5 Houston, Texas 77030-1038 Phone: (713) 686-7422 1 g C60-rich soot $10-$20 1 g mixed fullerene extract $500

Second Wave Of `Buckyball' Researchers Kicks Off Efforts

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