Ginley: polycrystalline thin films containing thallium will come along shortly. Indeed, as Hermann told attendees of last month's International Conference on the First Two Years of High-Temperature Superconductivity in Tuscaloosa, Ala., "I hope we can learn to replace thallium with something that's not so nasty to deal with." But finding new higher-T c superconducting compositions remains a great challenge. "All the obvious compositions have already been tried" many times over by many groups, Hermann tells C&EN. "We're really scratching our heads now." The solution might lie in a totally different chemical system, perhaps a noncopper one. Such an approach gained some credibility about two weeks ago when Robert J. Cava, Bertram Batlogg, and coworkers at AT&T Bell Laboratories announced the discovery of new superconducting oxides not based on copper. These new materials are bariumbismuth oxides containing either potassium or rubidium (C&EN, May 2, page 7). They are based on the parent compound BaBiC>3, with potassium or rubidium replacing some of the bariums. The new bismuth oxides have Tcs near 30 K, the operating temperature of the lanthanum copper oxides that triggered the superconductor revolution two years ago. The Bell Labs group magnetically measured the onset of superconductivi-
ty at 29.8 K in Bao.6Ko.4Bi03. This is the highest Tc value they have reported, and is significantly higher than the 13 K transition temperature achieved more than a decade ago in a closely related barium-leadbismuth oxide (BaPbo.75Bio.25O3). The hope is that scientists can further raise Tc in bismuth oxides by making other elemental substitutions. The synthesis of the bismuth oxides involved first grinding together oxides of the constituent metals (BaO, Bi2C>3, and an excess of KO2 or Rb20). The mixture was heated at 675 °C for three days inside a sealed silver tube. The resulting powder was annealed in flowing oxygen at 475 °C for 45 minutes, quickly cooled, and then pressed into pellets. Annealing for longer periods of time or at higher temperatures caused the loss of potassium from Ba-K-Bi-O compositions, the researchers say. The new bismuth oxides belong to the same mineral class (perovskites) as the copper oxide superconductors. But the bismuth oxides have a three-dimensional arrangement of bismuth and oxygen atoms rather than the layered arrangement found in the copper oxides. This means that properties such as critical current density are likely to be isotropic, or similar in all directions. In the copper oxides, by contrast, current flows much more efficiently along the copper planes than perpendicular to them. Thus, it may be easier to fashion high-performing superconducting wires and films from the bismuth oxides. Theoretical understanding of superconductivity also may benefit from the Bell Labs discovery. The missing copper, Batlogg predicts, "will stimulate some theorists to rethink their models for the underlying mechanism of high-T c superconductivity." Although the spotlight for the past few months has been trained on the new thallium and bismuth materials, investigation of the lanthanum and yttrium superconductors continues. The more researchers learn about these fascinating materials, the more questions they have. As Caen's Raveau recently noted with a great deal of understatement, "There is much to do in this field."D
Chemist wins NSF's Waterman award Peter G. Schultz, associate professor of chemistry at the University of California, Berkeley, recently was selected to receive the National Science Foundation's prestigious Alan T. Waterman Award. The award has been given annually since 1975 to an outstanding young researcher in any field of science, mathematics, or engineering. Schultz, who was selected from 128 nominees, is only the third chemist to win the Waterman award, which includes a medal and NSF grants of up to $500,000 over three years to fund research and advanced studies. Schultz was cited for "innovative research at the interface of chemistry and biology, both in the development of new approaches for the study of molecular recognition and catalysis and in the application of these studies to the design of selective biological catalysts." NSF Director Erich Bloch said of Schultz that "his achievements, in just two short years, have changed the way scientists think about bioorganic and biotechnologic areas and undoubtedly will continue to define the leading edge in this area of science." Of the award, Schultz says that "I am delighted to know that our work is really appreciated by the scientific community. It is also a great recognition for my s t u d e n t s , who started out not long ago setting up this lab from scratch." Because his research group has grown rapidly to more than 20 people, he also notes that the grants that accompany the award will be very useful. "We need to buy a lot more equipment, so the timing of the gift is perfect," he says. One area of Schultz's research singled out by NSF is his continuing investigation of catalytic antibodies. Independently, in 1986, Schultz and a group at the Research Institute of Scripps Clinic reported production of antibodies that catalyze, with a high degree of specificity, hydrolysis of esters and carbonates (C&EN, April 6, 1987, page 30). The antigenic molecules used to elicit these antibodies were phosphonates May 16, 1988 C&EN
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Science that mimic the tetrahedral transition state of the hydrolysis reaction. "One of our goals is to develop new strategies for generating highly selective catalysts/ 7 Schultz says. He points out that chemists are becoming increasingly proficient in the synthesis of selective catalysts for reactions involving small molecules. "However, if you want to do chemistry on a large molecule — DNA or peptides, for instance—you need structurally complex binding sites to recognize the substrates of interest." Antibodies naturally provide highly selective binding; the job of the chemist is to introduce catalytic activity. Schultz points out that there is a long history behind the efforts to produce catalytic antibodies. In 1948, Linus C. Pauling suggested that, whereas antibodies bind molecules in their ground state, enzymes preferentially bind the transition state of a reaction, thus stabilizing it relative to substrate and products. The stabilization reduces the activation energy of the reaction, thereby increasing the reaction rate. Schultz's initial catalytic antibodies followed a strategy suggested by Pauling's analysis of enzyme catalysis—that is, stabilization of the transition state of a reaction. Since then, the Berkeley chemists have d e v e l o p e d two a d d i t i o n a l approaches to producing catalytic antibodies. One approach uses antibodies to overcome entropic barriers to reaction. That is, the catalytic antibody binds and properly orients reactants in relation to each other to facilitate the reaction between them. Another approach involves introducing catalytic groups into the an-, tibody binding site. One way to accomplish this is to design the hapten—the molecule that elicits the antibodies—so that an amino acid residue with catalytic activity naturally is incorporated into the binding site. Schultz and coworkers have pursued this strategy in producing an antibody that catalyzes the photocleavage of thymine dimers in DNA. Other approaches to introducing catalytic groups are site-directed mutagenesis and direct chemical modification of the antibody, which Schultz also is pursuing. Schultz points out
Peter G. Schultz that, in addition to providing novel catalysts, the generation of catalytic antibodies may also shed light on the process of enzymic catalysis. Research on catalytic antibodies, however, makes up only about a third of the work in Schultz's lab. Another facet of his research is development of highly specific hybrid enzymes. For example, by attaching a synthetic oligonucleotide to a relatively nonspecific endonuclease, Schultz and coworkers were able to produce a highly specific enzyme that cleaves RNA and singlestranded DNA adjacent to the sequence complementary to the synthetic oligonucleotide [Science, 238, 1401 (1987)]. The chemists are working to extend this concept to production of hybrid enzymes that cleave double-stranded DNA. Another area of research in the award winner's lab is development of biosynthetic systems that will incorporate unnatural amino acids site selectively into proteins. "We are trying to interface biology with chemistry," Schultz says of his research. "We take advantage of chemistry to modify existing biological systems for our own ends." Schultz was born in 1956 in Cincinnati, Ohio. He received his B.S. degree in 1979 and Ph.D. degree in 1984 from California Institute of Technology, Pasadena. He joined the Berkeley faculty in 1985. Rudy Baum, San Francisco
