I
SCIENCE/TECHNOLOGY CONCENTRATES
Pressure effect on K3C60 superconductor The superconducting compound resulting from doping buckminsterfullerene with potassium, K3C60, shows a very large decrease in the temperature at which the compound becomes superconducting, Tc, with increas ing pressure, according to researchers at the University of California, Los Angeles, and Los Alamos National Laboratory [Science, 252, 1829 (1991)]. At atmospheric pressure, the Tc for K 3 C 60 is 19.3 K. According to the UCLA and LANL scientists, Tc drops precipitously with increasing pressure, reaching 8 Κ at 21 kilobars. This is among the strongest depressions of Tc as a function of pressure reported. According to the researchers, the re sults are at odds with two recently proposed theories on doped buckminsterfullerene superconductivity, and support the notion that the superconductivity of these compounds can be explained by the conventional Bardeen-Cooper-Schrieffer (BCS) theory of supercon ductivity in which electron pairing is mediated by electron-phonon coupling. The research was conducted by S.-M. Huang, R. B. Kaner, F. N. Diederich, R. L. Whetten, G. Grimer, and K. Holczer at UCLA and G. Sparn and J. D. Thompson at LANL.
Bow tie molecule trapped in the cold Spiropentadiene, a molecule that on paper looks like a bow tie, has been synthesized for the first time at Rice University in Houston [/. Am. Chem. Soc, 113, 5084 (1991)]. As the simplest spiro-connected ring sys tem with two olefinic bonds, spiropentadiene "is of considerable theoretical interest since the two π sys tems are held in perpendicular planes by a common carbon and are predicted to experience significant spiroconjugation," note the compound's creators, chemis try professor W. Edward Billups and former graduate student Michael M. Haley. They obtained the highly strained molecule by first preparing its precursor, a spiropentane in which each ring is adorned with a chloro and trimethylsilyl group on different carbons. Exposing this precursor to tetra-n-butylammonium fluoride in a vacuum at room temperature led to elim ination of all the substituents. The resulting spiropen tadiene was condensed out in a liquid nitrogen trap. It survived for about 20 minutes at -105 °C before poly merizing. Spiropentadiene also was trapped as a Diels-Alder adduct by reaction with cyclopentadiene. The Houston chemists are now studying the proper ties of this intriguing "textbook molecule/'
Tetraethynylethylene synthesized Chemists at the University of California, Los Angeles, have made tetraethynylethylene, a precursor of cer tain long-sought, possibly electrically conducting polymers and carbon allotropes [Angew. Chem., Intl. Ed. Engl, 30, 698 (1991)]. Organic chemistry professor François Diederich, graduate student Yves Rubin, and crystallographer Carolyn B. Knobler point out that the compound is the only known C 10 H 4 . It can be linearly polymerized through the ethynyl groups to form 40
July 1, 1991 C&EN
polycarbon networks. It might also be cyclopolymerized to poly-l,8:4,5-naphthalene, which could be dopable to a state of conductivity or superconductivity. The compound is an example of a cross-conjugated system in which each ethynyl group is in conjugation with both the one cis to it and the one trans to it. And as double enediyne systems, its derivatives might have anticancer properties (C&EN, May 6, page 31). The work was supported by the National Science Foundation.
Zachary Taylor not killed by arsenic Analyses of tissue samples have failed to support the notion that Zachary Taylor, 12th President of the U.S., died of arsenic poisoning. According to the history books, Taylor died of gastroenteritis on July 9, 1850, perhaps as a result of eating tainted food. However, Clara Rising, a Florida author working on a book about Taylor, recently speculated that he had instead been poisoned by arsenic—assassinated because of his opposition to slavery in new states seeking admission to the Union. After Rising furnished circumstantial evidence and paid a $1200 autopsy fee, Kentucky officials exhumed Taylor from his Louisville crypt and took tissue samples including hair, nails, and bone scrapings. The samples were examined by neutron activation analysis at Oak Ridge National Laboratory and by spectrometric methods at two Kentucky labs. According to pathologist George Nichols, Kentucky medical examiner, the tests revealed trace amounts of arsenic in the tissues, but far less than needed to cause symptoms of arsenic poisoning. In Nichols' opinion, Taylor died of "one of a myriad of natural diseases which would have produced the symptoms of gastroenteritis."
EDUCATION Texas, California to pick textbooks jointly Texas and California, in an agreement that could affect the content of science textbooks across the U.S., announced last week that they will jointly select science textbooks for their public schools. The two states are the largest purchasers of textbooks in the nation. Thus, the books they choose may end up in most American classrooms because publishers generally market their biggest selling books nationwide. Texas and California plan to commission the same science textbooks for a new instructional program being developed for seventh- and eighth-grade students in both states. The new approach followed by these books differs from the traditional teaching of science in that it uses major themes to instruct students in several areas of science with each lesson. The lessons blend biology, chemistry, physics, and Earth/space science. "The idea is to show students that if we use these basic [scientific] concepts every day, there is nothing to be afraid of in science/ 7 says Jim Collins of the Texas Education Agency.
