SCIENCE/TECHNOLOGY CONCENTRATES • Method improves adherence of diamond film to metals, ceramics Florida researchers have developed an improved way to make a diamond film adhere to the surface of a steel or tungsten carbide/cobalt composite. Coating these substrates with diamond makes them extra resistant to wear, corrosion, and erosion—and thus of great interest for cutting tools and other applications. But because the substrate and coating materials have significantly different thermal expansion coefficients, temperature changes lead to very high stresses in the coating. This causes the diamond film to crack and peel off. Methods to improve the adhesion of diamond coatings have been only partially successful, says Rajiv K. Singh, associate professor of materials science and engineering at the University of Florida, Gainesville. He and his coworkers now report a way to etch the substrate surface with a laser beam to give it a smooth, hill-and-valley topography [Science, 272, 396 (1996)]. When the diamond film is then laid down using a chemical vapor deposition technique, the substrate-diamond interface thus created linearly changes composition (and thermal expansion behavior) from 0% to 100% diamond. Tests performed by the researchers indicate "significantly better" adhesion of the diamond film than has been seen previously, Singh tells C&EN.
• Genetically engineered plants reduce soil mercury Plants often have "excess reducing power" from photosynthesis that can be tapped to reduce toxic metal ions, researchers suggest. Genetics professor Richard B. Meagher and colleagues at the University of Georgia, along with postdoctoral associate H. Dayton Wilde of Westvaco's Forest Science Laboratory in Summerville, S.C., have demonstrated this possibility by genetically engineering a plant not only to absorb and concentrate Hg^+ ions from soil, but also to reduce them to less toxic elemental mercury [Proc. Natl. Acad. Sci. USA, 93,3183 (1996)]. Certain soil bacteria are known to reduce highly toxic organomercury compounds to metallic mercury through the action of a mercuric ion reductase called MerA. The researchers modified the bacterial merA gene and inserted it into Arabidopsis tlwliana plants. While control plants died in medium containing 25 pM HgCl2, the transgenic plants grew well at 50-100 jaM HgCl2/ producing elemental mercury, which they released into the air. The plants may also be reducing Au3+ to elemental gold, a less toxic form of that metal that presumably precipitates in the plant cells. The gene might be further modified, the researchers suggest, to reduce and lower the toxicity of other heavy-metal ion pollutants such as Cu2+ and Pb2+.
• Small temperature changes cause soils to release, absorb C0 2 Relatively small atmospheric temperature variations could cause the rapid exchange of carbon in soils with carbon in the atmosphere, creating significant changes in carbon dioxide levels, California scientists report. Using carbon and carbon-14 measurements in soils taken along a temperature gradient in the Sierra Nevada mountain range in California, the scientists showed that 50 to 90% of organic 34
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carbon added to these soils by plants remains only several decades before returning to the atmosphere through decomposition. Carbon turnover is faster at sites with higher temperatures [Science, 272, 393 (1996)]. Susan E. Trumbore, Earth system science professor at the University of California, Irvine, and colleagues Oliver A. Chadwick at UC Santa Barbara and Ronald Amundson at UC Berkeley, were able to infer turnover rates from the increase in C between soils sampled in the 1950s and the 1990s. Testing of nuclear weapons in the early 1960s approximately doubled the amount of 14C in the atmosphere. The amount of 14 C increase observed in soils since then reflects the rate at which soils are exchanging carbon with the atmosphere. Noting the strong relationship between turnover times and temperatures, the group calculated that a warming of 0.5 °C could cause a 6% overall decrease in rapidly cycling soil carbon. Conversely, widespread cooling could cause temporary storage of carbon in soils.
• Biotechnology pioneers Cohen, Boyer share $500,000 prize Genetic engineers Herbert W. Boyer and Stanley N. Cohen— the scientists who developed recombinant DNA technology—are winners of the second annual $500,000 LemelsonMIT Prize for excellence in invention and innovation. Cohen, professor of genetics and medicine at Stanford University School of Medicine, and Boyer, professor emeritus of biochemistry and biophysics at the University of California, San Francisco, collaborated in the early 1970s on methods for cloning genetically engineered molecules in foreign cells. Boyer later cofounded Genentech, the South San Franciscobased biotechnology firm. The three patents on basic cloning methodology awarded to Boyer and Cohen and their institutions underpin the multi-billion-dollar biotechnology industry. The prize, first awarded last year, is funded by independent inventor Jerome H. Lemelson.
EDUCATION • New name for Harvard's chemistry department reflects broadened scope Effective July 1, the department of chemistry at Harvard University will change its name to the department of chemistry and chemical biology. The change brings to fruition a suggestion made in 1989 by Nobel Laureate Konrad Bloch, Higgins Professor of Biochemistry Emeritus. Noting that many of his senior colleagues were pursuing bioorganic, bioinorganic, biochemical, and biophysical problems, Bloch indicated that the new name would be a recognition of reality, says David A. Evans, chairman of the department. Bloch's suggestion languished, explains chemistry professor Gregory L. Verdine, until the department acquired faculty members who have concentrated their research in "what could be called chemical biology/' Verdine defines this fundamentally integrative field as one where scientists use whatever technique it takes to solve complex scientific problems in the biological sciences. Chemical biology "trains people to cut across fields," he says, noting that his own research in DNA damage and repair often requires chemical synthesis of protein inhibitors.
