SCIENCE & TECHNOLOGY
their own areas of expertise and to attend presentations on topics that they typically would not attend. By design, the subjects of the plenary lectures varied widely. All of the presentations focused on research in catalytic chemical transformations, yet the systems Conference aims to foster unified approach studied, the methods of investigation, and to field's DISPARATE TOPICS the character of the presentations were deMITCH JACOBY, C&EN CHICAGO rived from laboratory cultures as disparate as biology and physics. One of the most biological lectures was given by Berkeley's Carolyn Bertozzi, a "HOMOGENEOUS, heterogeneous, and of the distinct reaction conditions under chemistry and biology professor. Bertozzi enzyme catalysis are three totally separate which various types of catalysts are used. marveled at the "exquisite selectivity in areas of chemistry," proclaimed Gabor Heterogeneous catalysts tend to be used biological catalysis," noting, for example, A. Somorjai last month at the opening of to facilitate high-temperature gas-phase that enzymes active in cellular processes the 13th International Symposium on the reactions. Homogeneous catalysts are genmanage to target specific reactants from Relations between Homogeneous & Heterally used in organic solvents at moderate among many thousands of similar molerogeneous Catalysis. "Comparing one temperatures. And enzymes typically work ecules. Scientists have field to another has long attributed a good traditionally been like D Y N A M I C DUO Racemic mixtures can part of that specificity comparing apples to be transformed enantioselectively by couto the unique threeoranges." It shouldn't pling an enzyme (Candida antarctica lipase dimensional structure be this way, Somorjai B, left) with a homogeneous diruthenium and chemical composaid, "because the mocatalyst in a process known as dynamic sition of an enzyme's lecular fundamentals kinetic resolution. active site, which is of all three fields are tailored for molecular identical." recognition. As he sees it, caAnother differtalysis research ought entiating feature of to be unified, and he biological catalysis suggested a way to do derives from the role that: Investigate all Ph Ph of cellular compartcatalysts on the moc o o c mentalization. As Berlecular scale and unO O O O tozzi explained, cerder the same types of Ph = phenyl tain types of cells are reaction conditions. composed of memBy doing so, Somorjai continued, "we can uncover molecular in water near room temperature. As a result brane-enclosed organelles that carry out enzymatic transformations on molecules ingredients in one type of catalysis and use of such practical differences, devotees of passing through them. One example under them to help us understand another type." each of the three subdisciplines developed study in Bertozzi's lab involves proteins With those words, Somorjai, a longtime unique ways of describing, characterizing, that travel from the endoplasmic reticulum leader in the arena of surface science, a field and thinking about their respective classes (the tube-like organelles that host most closely related to catalysis, urged attendees of catalysts. protein synthesis) through the various to think about problems in catalysis science compartments within the Golgi apparatus broadly and in nontraditional ways. Held TO STIMULATE creative and broad think(a layered organelle where certain proteins last month on the tree-lined and scenic cam- ing that encompasses all areas of catalysis, are packaged). As the proteins make this pus of the University of California, Berkeley, Somorjai invited a number of internationjourney, they are altered sequentially by where Somorjai is a chemistry professor, the ally recognized experts in each of the three glycotransferases and sulfotransferases, meeting drew more than 300 people from areas to address the entire conference. In which modify the proteins by adding sugar around the globe, including some who travthat way, the meeting provided particiand sulfate units, respectively. Those modieled from Inner Mongolia and elsewhere pants with opportunities to learn about fications are believed to play important in Asia. The turnout was twice as large as major themes in catalysis that lie far from Somorjai had initially planned for, a result he was pleased to attribute, in part, to the strong interest of young scientists in applying catalysis in the red-hot areas of green chemistry and nanotechnology. The three principal areas of catalysis evolved independently, mainly because
COMING TOGETHER ON CATALYSIS
We can uncover molecular ingredients in one type of catalysis and use them to help us understand another type."
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roles in cellular signaling processes central interpreting experimental results, designing to inflammatory diseases such as arthritis future experiments, and developing new and asthma. and improved types of catalysts. On the experimental side of surface caAt the other end of the catalysis spectrum talysis, Freund, a professor and director of in the meeting's agenda were physics-centered presentations such as the ones led by Jens K. N0rskov and HansJoachim (Hajo) Freund on heterogeneous (solid-state) catalysis. N0rskov, a physics professor at the Technical University of Denmark, Lyngby, reported on state-of-the-art quantum mechanical calculations that probe the origins of differences in chemical reactivity of various transition-metal and nanoparticle surfaces. By carrying out computer "experiments" that compare the properties of various crystal faces of certain metals and the effects of sulfur or the Backvall Somorjai presence of other foreign atoms that can inactivate or otherwise "poison" the Fritz Haber Institute of the Max Planck catalysts, N0rskov and coworkers have Society, in Berlin, reviewed studies of developed tools to distinguish between model catalyst systems that were designed, geometrical (structural) and electronic facin his words, "to catch some of the comtors that control the chemical reactivity of plexity of real catalysts." The surfaces of solid surfaces. Such studies are essential for
real catalysts are often dotted with crystal defects, which can serve as active sites that mediate reactions. For example, oxygen vacancies in metal oxides, which can be occupied by either one or two electrons, have been suspected of playing such a role, but the defects have been tough to characterize precisely. On the basis of spectroscopy and microscopy studies, Freund's team has shown that it can prepare model MgO films in which the two types of defects are readily identified and distinguished (J. Phys. Chem. B 2006, no, 46). Other speakers at the symposium drew upon investigations that straddled at least two of the principal areas of catalysis in one way or another. For example, chemist Jan-Erling Backvall of Stockholm University, in Sweden, described a process based on an enzyme and a homogeneous catalyst that work in concert in an organic solvent to yield highly enantiopure products (C&EN, Aug. 14,2006, page 29). Known as dynamic kinetic resolution, Backvall's procedure, which initially was
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SCIENCE & TECHNOLOGY
applied to chiral secondary alcohols and shapes. Typically, the group decomposes has been commercialized by DSM, in the organometallic precursors in solution to Netherlands, for production of intermediform metal nanoparticles and then treats ates, employs a ruthenium-based racemiza the resulting particles with various ligands tion catalyst and an enzyme (a lipase) to to control the morphology of the products. transform the alcohols into esters. As enzyme-catalyzed acylation selectively converts one of the alcohol enantiomers to the product, the ruthenium catalyst interconverts the nonreacting enantiomer to the reactive form. In that way, the technique can convert more than 90% of the starting material with nearly 100% enantioselectivity. Backvall pointed out that his research group has developed similar procedures for resolving enantiomers of amines, diols, and other types of racemic mixtures. Meanwhile, Bruno Ghaudret, who leads a group at the National Center Chaudret Marks for Scientific Research (CNRS) in Toulouse, France, takes advantage of soluUsing thiols, amines, and other types of tion-phase methods and organometallic ligands to control product stability, the recomplexes to synthesize nanostructured searchers have synthesized nanorods, nanmaterials—often heterogeneous cataocubes, and other nanoscale structures. lysts—in a variety of well-defined sizes and In one application of these synthesis
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methods, the Toulouse group examined the propensity of palladium nanoparticles coordinated to chiral diphosphite ligands to catalyze transformations of racemic mixtures. Their tests showed that the materials prepared in that way perform as fairly selective catalysts for C-C coupling reactions—specifically, asymmetric allylic alkylations. A couple of days' worth of talks on a broad range of catalysis topics is not enough to change the way mature scientists think about their research. Nonetheless, for some leading chemists, the benefits of such a gathering are tangible. "Ifindit stimulating and scientifically productive to bring people working in these diverse disciplines together," commented Northwestern University chemist TobinJ.Marks. Bringing together such a diversity of expertise, Marks noted, "provides an opportunity to bounce your ideas off people from different disciplines and sometimes to obtain novel feedback you wouldn't get from your usual audience." •
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