NEWS OF THE W EEK
NANOGOLD OXIDIZES ALONE CATALYSIS: Small gold clusters
add oxygen to styrene without help from additives
S
HRINK GOLD nanoparticles down to a mere 1.4 nm in diameter and they can catalyze selective oxidation reactions without the help of support materials or additives that are normally required, according to a new study. Gold has long been known to have size-dependent catalytic activity: The metal is inert in bulk, whereas gold nanoparticles 3 to 5 nm in diameter can catalyze a variety of reactions. But those larger nanoparticles require the addition of H2 or peroxide species to drive the reaction, or an electronic interaction with a support material such as titanium dioxide. A group led by Richard M. Lambert, a chemistry professor at Cambridge University, has now reported that 55-atom gold clusters supported on inert material can catalyze the reaction of O2 with styrene to produce
styrene oxide without the need for additives (Nature 2008, 454, 981). Getting rid of additives makes the system more environmentally friendly. The particles likely adsorb and dissociate O2 into individual O atoms on the surface of the clusters. Then the O atoms initiate the reaction with styrene, Lambert says. Oxygenated hydrocarbons, in particular epoxides such as styrene oxide, are used in a variety of commercial chemical applications. The use of cluster chemistry to prepare the catalysts seems to be “a convenient and direct route to produce particles too small to be easily synthesized by conventional preparation methods,” says D. Wayne Goodman, a chemistry professor at Texas A&M University, in a commentary accompanying the report. He adds that the cluster particles conform to a very narrow and reproducible size distribution, unlike the products of traditional catalyst preparation. The cluster-based system could also be extended to other metals or other classes of reactions, including the industrially important epoxidation of propylene, Lambert says. “Going down to such small particle sizes could also trigger other kinds of unexpected chemistry,” he adds, referencing single-crystal studies in which reactions are sensitive to the geometry of crystal surfaces. —JYLLIAN KEMSLEY
POLYMER SHRINKS AND SWELLS
autonomous matter transporters or self-beating micropumps that could function without external control.” The new gel, composed of a cross-linked polymer and ruthenium, is activated by dunking it in a solution of citric acid, which sets off the BZ reaction. Eventually, the reGEL PROPULSION: Exotic oscillating action medium gets spent, but with the addition of more reaction moves matter citric acid, the process starts over again, Maeda explains. The discovery comes on the heels of work from Kenichi Koshigawa at the University of Kyoto and colleagues, who also studied the BZ reaction’s potential to move HE OSCILLATING Belousov-Zhabotinsky (BZ) matter ( J. Phys. Chem. C 2007, 112, 3032). Rather than the reaction, famous for producing dazzling colorswelling and shrinking of gels, their system harnesses changing patterns, is now also finding use as a a solution that undergoes the BZ reaction. They were novel way to move matter. able to use that to propel a small piece of paper along the Shingo Maeda of Waseda University, in Tokyo, chemical wave fronts. and colleagues designed a polymer gel that undulates Koshigawa notes that the with a peristaltic motion simitransport speed of the Waseda lar to the way cilia or intestinal PULSATING Polymer gel propels group’s gel is still slow (about muscles pulse with rhythmical, an object along chemical waves. 1 mm per minute) compared directional contractions. As the with that of their solution (about gel undergoes the BZ reaction, a Chemical wave 10 mm per minute). “The reruthenium catalyst periodically maining problem is how to changes its oxidation state back speed up the deformation rate,” and forth, generating chemical Koshigawa says referring to the waves that propagate outward, polymer system. causing the gel to shrink and t Maeda points out that the swell (Angew. Chem. Int. Ed. 2008, composition of the gels actually 47, 6690). changes during the reaction, The authors write that they making possible a wider range of envision use of the phenomenon applications than Koshigawa’s to develop lifelike systems— strategy. —ELIZABETH WILSON “biomimetic devices such as SHIN GO MAEDA
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Styrene O2, gold catalyst
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Styrene oxide
