NEWS OF THE WEEK
CRYSTALS' SHAPE SHIFTS IN A FLASH MATERIALS ENGINEERING: Light induces
crystals to bend without breaking
S
HINE A LITTLE ultraviolet light on the crystals in Masahiro Irie's lab at Japan's Kyushu University and something unusual happens: The crystals' shape changes—shrinking in one instance, going from a
C R Y S T A L C H A N G E S UV light changes the shape and color of a molecular crystal of l,2-bis(2-ethyl-5-phenyl-3-thienyl)perfluorocyclopentene. Visible light reverses the change.
X = 365 nm X > 500 nm
Et = ethyl
10 ym
rectangle to a parallelogram in another, and bending but not breaking in a third (Nature 2007,446,778). Shine visible light on the deformed crystals, and they'll shift back to their original shape. The effects take place in a matter of microseconds— far faster than similar phenomena previously observed in liquid crystals and polymers, Irie says, suggesting that the crystals could be used as components in microscale devices. According to Irie and coworkers, the shape shifting occurs as the result of an electrocyclic reaction that transforms the open-ring isomers of diarylethene chromophores into their corresponding closed-ring isomers. Yale University chemistry professor J. Michael McBride calls the development "a breakthrough" in the area of device fabrication. "Along-cherished aim" of solid-state organic chemistry is "to discover new single-crystal to single-crystal transformations, with a smooth transition between the crystal lattices of the starting material and the product," he writes in a commentary that accompanies the paper. Rod-shaped crystals, in one example, bent and straightened 80 times in response to light before losing the shape-shifting trait. Irie's group showed that one crystalline rod could behave like a light-activated slingshot, launching a gold microparticle that weighed 90 times more than the crystal itself over a distance of 30 urn. "An improved understanding of this unexpected resilience is required, along with a method to assemble microscale components, if we are ever to make a useful chemicomechanical device from such materials," McBride adds. "But simply demonstrating this behavior suggests a possibility that previously seemed remote."—BETHANY HALFORD
SWEETENER WARS Companies duke it out over Splenda ads Three little chlorine atoms are causing quite a stir in the artificial sweeteners market. A trial that began in a Philadelphia court last week pits Chicago-based Merisant, maker of Equal and NutraSweet, against McNeil Nutritionals, the marketer of Splenda. Merisant's suit centers on McNeil's Splenda advertising, which says the product is "made from sugar, so it tastes like sugar." Merisant claims that the wording gives Splenda an unfair competitive edge by misleading consumers into thinking the product is more natural than other artificial sweeteners. * Sucrose is indeed the starting material for Splenda, but the molecule is modi-
tied by replacing each of three hydroxyl groups with a chlorine atom. The resulting compound, called sucralose, is then blended with small amounts of maltodex trin and dextrose. Since its approval OH as a general-purpose sweetener in 1999, Splenda has eclipsed Equal in the lucrative artificial sweeteners market. In the suit, Merisant implies that demand for Splenda is correlated with consumer perception that it is "natural." The company notes that sales of Splenda were weak in 2001, when McNeil launched an ad campaign saying the sweetener
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is made from sugar and including the phrase "but it's not sugar." Further complicating the sweetener wars, Tate & Lyle, the manufacturer of sucralose, has filed an International Trade Commission case against three Chinese manufacturers and 18 importers and distributors alleging they are infringing patents on its sucralose production process. The move follows a federal suit initiated last year against one of the defendants in the current complaint. Tate & Lyle manufactures sucralose in Mcintosh, Ala., and in Singapore.—LISA JARVIS
