COPPER-FREE CLICK CHEMISTRY CHEMICAL BIOLOGY: Reagent for labeling biomolecules eliminates need for toxic metal catalyst
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NEW REAGENT developed by chemistry professor Carolyn R. Bertozzi and coworkers at the University of California, Berkeley, eliminates the toxicity usually associated with a rapid and irreversible reaction strategy commonly known as click chemistry (Proc. Natl. Acad. Sci. USA, DOI: 10.1072/ pnas.0707090104). This tweak to remove copper catalysts makes the reaction—azide-alkyne cycloaddition—biologically friendly and thus useful for labeling biomolecules in cells. The reagent helps Bertozzi and her team study dynamic biochemical processes that are otherwise difficult to follow in real time. Bertozzi is particularly interested in studying glycosylation, the addition of sugar molecules to proteins. The reaction is tough to track because the sugar molecules, or glycans, are continuously recycled. “Most imaging of carbohydrates uses fixed systems,” says Jeremy M. Baskin, a grad student and a member of the team that developed the reagent. “You can take a snapshot, but
you can’t make the equivalent of a movie.” F Azides make a handy tag for labeling biomolecules. They don’t react with other molF ecules in the system, and they can be added O to a range of biomolecules, including sugars, R N lipids, and proteins. O H Unfortunately, the two reactions most R = fluorescent dye or biotin commonly used to affix fluorescent or other Difluorinated cyclooctyne labels to azide-tagged biomolecules have limitations. The Staudinger ligation, which forms an amide bond between the azide and an esterderivatized phosphine, is too slow. Azide-alkyne cycloaddition is much faster, but the conventional copper catalysts required are toxic to living systems. Bertozzi’s team has designed a reagent that eliminates those copper catalysts. “This copper-free chemistry is really designed for applications that require this extra burden of nontoxicity,” Baskin says. “I see it as one reaction in a family of click chemistries.” The UC Berkeley researchers speed up the reaction even without a catalyst by using a difluorinated cycloCopper-free octyne instead of the usual terminal alkyne. The ring click chemistry strain and the electron-withdrawing difluoro group labels cell surface activate the alkyne for copper-free click chemistry. carbohydrates Bertozzi and coworkers use the reagent to attach (green), which then fluorescent labels to cells with azide-containing sialic move inside the cell. acid in their surface glycans. The team studied the dynamics of glycan trafficking over the course of 24 hours with no indication that the reaction or the labels perturb the process. —CELIA ARNAUD
ALTERNATIVE ENERGY Universities compete in third solar decathlon CHERYL HOGUE/C&EN (BOTH)
10 categories. Seven categories focused on energy use, and others included comfort and marketability. Each team received $100,000 from event sponsors, about half of what they needed for the competition. Home designs relied strongly on passive heat and efficiency to cut electricity demand. Carnegie Mellon University’s home (far left) incorporated a living wall and roof—a “greenscape” of plants to help cool the house in Washington’s heat. The University of Cincinnati relied on another wall, one with 120 tubular thermal collectors to meet other household heating and cooling needs. All homes used solar cells and batteries to meet energy demands. Underscoring the event’s importance, DOE says some 70% of U.S. electricity is used to operate buildings.—JEFF JOHNSON
Twenty student teams from universities in the U.S., Puerto Rico, Germany, and Spain arrived in Washington, D.C., for the third Solar Decathlon, sponsored by
the energy industry and the Department of Energy and held Oct. 12–20 on the National Mall. The student teams assembled real-life, 800-sq-foot, super-efficient homes. All were completely sun-powered, with sufficient energy to light, heat, and cool the home; run a full kitchen; and charge a small electric vehicle. Like athletes in an Olympic track and field decathlon, the teams competed in
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