SCIENCE/TECHNOLOGY
The Tetrahymena ribozyme has been selected to splice itself out of an rRNA precursor, Cech points out, not to cata lyze the hydrolysis of aminoacyl ester linkages. Thus it is not surprising that it doesn't catalyze the latter reaction all that well. Cech believes it will be possi ble to create ribozymes that will be much better at catalyzing the esterase reaction. Efforts are under way in his laboratory to create such ribozymes to facilitate further studies on the chemis try of the catalytic reaction. Concerning origin of life theories, Cech comments: "The scenario has al ways been that you could start out with a nucleic acid replicating itself. That could be the origin of the first selfreplicating system. But you could not go very far from that unless you get into the protein world. You have to be able to make information-encoded pro teins without invoking proteins to cata lyze the process. "What do you need to get that done? You need tRNAs and mRNAs. That's all right, you are allowed to use them because we are saying that RNA mole cules exist. How do you get protein synthesis going? From Noller's work, it looks like the rRNA by itself might have primitive peptidyl transferase ac tivity, even without any protein. What else do you need? You need tRNA syn thetases, a way of attaching the amino acids to the tRNAs. We may be seeing a hint of that, because that is the reverse reaction of our ribozyme-catalyzed es terase reaction." Weiner thinks the reports from Noller and Cech are not all that surprising. "In 1968, Francis Crick was the first to say that the composition of the ribosome is telling us something," Weiner says. "He pointed out that the job of the ribosome is to make protein, but there could not have been good proteins around when it started doing its job. Therefore, the RNA must be the component that originally was synthesizing the protein. The pro teins joined in later." Once Cech and Altman demonstrat ed that RNA could catalyze reactions, Crick's idea took on new life, Weiner continues. Data on antibiotic resistance and ribosome inactivation all point to ward the rRNA being the catalytic component of ribosomes. "So I think these results make it more plausible that RNA came before protein," Wein er concludes. "Even though we all sort of believed that already." • 24
JUNE 22,1992 C&EN
More buckminsterfiiUerene derivatives prepared Back-to-back communications in the most recent issue of the Journal of the American Chemical Society describe the synthesis and characterization of two new derivatives of C60. John R. Morton and Keith F. Preston, of the National Research Council of Can ada, Ottawa, and Paul J. Krusic, Steve A. Hill, and Ed Wasserman, of Du Pont Central Research & Development, Wilmington, have shown that alkyl rad icals (R') react with C^ to form RC^' radical adducts [/. Am. Chem. Soc, 114, 5454 (1992)]. The chemists characterize these compounds with electron spin res onance (ESR) spectroscopy. Cso has the structure of a truncated icosahedron—a polygon made up of 20 hexagons and 12 pentagons. All of the carbon atoms in C^ are equivalent, but there are two types of carbon-carbon bonds, a shorter "double" bond at the fusion of two six-membered rings and a longer "single" bond at the fusion of a six- and a five-membered ring. The NRC and Du Pont chemists gen erate terf-butyl, 1-adamantyl, isopropyl, or trichloromethyl radicals in a C^ solution. The radicals rapidly add to the fullerene to form the RC60* radical. According to Krusic, the ESR spectra of the fullerene radical species indicate that the unpaired electron in RC60' is not delocalized over the entire C 60 sphere. Rather, it is largely confined to five carbon atoms in the two fused six-
Computer graphic depicts structure of (CHJCC60 dimer; bulky tert~butyl substituents result in relatively weak bond between the two C60s
membered rings to which the alkyl group attaches. The dependence of the ESR signal in tensity on temperature and on concen tration at a fixed temperature indicates that the radical adducts of C^ exist in equilibrium with their dimers, Krusic says. In these dumbbell-shaped mole cules, the two C^ moieties are linked di rectly to each other. This is the first ex ample of a bond linking two fullerenes. The research groups showed that the strength of the bond uniting the two halves of the RC60-C60R molecules de pends strongly on the size of the radi cal that originally added to C60. There fore, this bond must be between carbon atoms close to the carbon bearing the alkyl group. For terf-butyl, the bond strength in the dimer is 22.1 kcal per mole; for the smaller isopropyl group, the bond strength increases to 35.5 kcal per mole. At the University of California, Davis, chemistry professor Alan L. Balch and coworkers Vincent J. Catalano, Joong W. Lee, and Marilyn M. Olmstead had pre viously shown that the iridium com pound, Ir(CO)Cl[P(C6H5)3]2, reacts with C^ and C70 to give single η 2 products.
I
Computer graphic depicts the interaction, determined by x-ray crystallography, of two molecules of (it)2-C60)Ir(CO)Cl[C^CHzOCfitCH^iCJl^ with carbon atoms in blue, oxygen in red, chlorine in green, phosphorus in lavender, and iridium in yellow (hydrogen atoms are not shown); two Cfi5CH2OCfi4CH2 "arms" from one molecule embrace the C^ portion of the adjacent molecule
The iridium adds to the fusion of two six-membered rings in the fullerene. The Davis chemists, in research sup ported by the National Science Foun dation, found that the crystal of the iridium-C60 adduct, (r|2-C60)Ir(CO)Cl[P(C6H5)3]2, contains five disordered benzene solvent molecules. This obser vation suggested to them that it "might be possible to construct molecules that provide a host—a molecular egg crate— into which C^ might nest," Balch says. Balch and coworkers designed new ligands that contain flat aromatic rings connected with sufficient flexibility to accommodate pi-pi interactions with the
curved exterior of QQ. Specifically, they prepared C6H5CH2OC6H4CH2P(C6H5)2, which they designate bobPPh2. This compound was used to prepare an iridi um compound, Ir(CO)Cl(bobPPh2)2, that they reacted with C^ to produce (η2C60)Ir(CO)Cl(bobPPh2)2 [/. Am. Chem. Soc., 114,5455 (1992)]. Crystallographic characterization of this iridium-C60 molecule shows that the two arms of the phosphine ligands reach out to cradle the C60 portion of an adjacent molecule. The interactions continue on to the next molecule so that an infinite chain results. Rudy M. Baum
ACHEMASIA repeats, featuring basic systems Joseph Haggin, C&EN Chicago In a world of economic recession and political change, how to handle busi ness and technology dealings with Chi na has been something of a puzzle for many Western companies—especially in light of the Chinese government's crackdown on dissent at Tiananmen Square in Beijing in June 1989. For the international chemical technology com munity, that predicament has been ex emplified in reactions to ACHEM ASIA, an international meeting on chemical engineering and biotechnolo gy first held in 1989 not long after the Tiananmen Square events. Last month, ACHEMASIA took to the floor at Beijing's China International Ex. hibition Center for the second time. Par ticipation by exhibitors and presenters was down 25% from the first meeting. Nevertheless, the official commitment to ACHEMASIA remains strong. The meeting and exposition are a Far Eastern equivalent to Germany's ACHEMA, held every third year in Frankfurt and generally recognized as the largest exhibition-congress in the world for chemical plant equipment and engineering. As with ACHEMA, ACHEMASIA is organized by Ger many's Deutsche Gesellschaft für Chemisches Apparatewesen, Chemische Tecknik und Biotechnolgie, known familiarly as DECHEMA. In its organizing role for ACHEMASIA, DECHEMA is supported by the Chemical Industry & Engineering Society of China, the Ministry of Chemical Industry, and other high-ranking institutions from neighboring Asian countries.
In an assessment of the first two ACHEMASIA conclaves, DECHEMA president Gerhard Kreysa lamented the Tiananmen Square events. They amounted to a "specter hovering over the proceedings of ACHEMASIA '89," he said. For some time it was not certain that the first ACHEMASIA would even be held. A number of exhibitors withdrew even though they lost their deposits in the process. The period between 1989 and 1992 was one of deepening global recession and cooling of diplomatic relations between China and most other countries. Kreysa suggested that these problems alone were more than enough to daunt the organizers in their efforts to promote ACHEMASIA. However, Kreysa said, DECHEMA is convinced that Chi-
na's continuing efforts to open the country to outside contacts are genuine and worthy of reciprocation. DECHEMA's reciprocation is expressed in its commitment to ACHEMASIA. Although ACHEMASIA was organized by a German group, more than half of the exhibitors were from Asia. Of the 245 exhibitors listed for the event, 105 were from China, 109 from Europe (including 69 from Germany), 24 from the rest of Asia, and seven from the U.S. The inference of the heavy German representation is that it reflects German interest in penetrating Chinese markets. This is true, Kreysa noted, but the recent reunification of Germany has attenuated the country's efforts elsewhere. Kreysa touched on the "immense task" of restoring the economy of Eastern Europe. That effort has diverted attention from other enterprises and, correspondingly, diminished capital available elsewhere. However, Kreysa believes that this is only a temporary development and will certainly not eliminate the need for global economic cooperation and technology transfer in the long term. China's view about all of this is guardedly optimistic. He Guoqiang, vice minister of chemical industry in China, reaffirms China's intention to double the chemical industry's contribution to the gross national product by the end of the century. Others familiar with the industry agree that this is possible, but it will be accomplished more by modernizing existing industries than by appending new ones. As one observer put it, "They
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China International Exhibition Center in Beijing was site of ACHEMASIA meeting JUNE 22,1992 C&EN
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