Science Concentrates

Peptide shuttles copper

In many bacteria that oxidize methane, copper plays a central role in metabolism, including the regulation of enzymes involved in methane oxidation. Getting appropriate amounts of copper requires that these organisms take up larger amounts of copper than most bacteria while still protecting themselves from copper toxicity. David W. Graham of the University of Kansas and coworkers there and at Iowa State University and Kansas State University report the crystal structure of a candidate for such a function--a compound they dub methanobactin, a small fluorescent peptide that contains one copper ion per molecule [Science, 305, 1612 (2004)]. Methanobactin has a compact, pyramid-like shape, with the metal-binding site located at the base of the pyramid. The primary sequence of the peptide contains both amino acid and non-amino acid residues. The unusual copper coordination site (shown) is formed by two of the non-amino acid residues, thionyl-containing imidazole chromophores, which form a complex with the copper through their nitrogen and sulfur atoms.

Gas-sensing nanoflowers

Superhydrophobic, three-dimensional tin dioxide flowers with nanoporous petals have been prepared by chemists at Lakehead University, Ontario [Chem. Commun., 2004, 1964]. SnO₂ is a thermodynamically stable semiconductor that is highly sensitive to reducing gases such as carbon monoxide. "The high surface-to-volume ratio and superhydrophobic properties of the SnO₂ nanoflowers are extremely promising for a new class of gas sensors," Aicheng Chen says. He and his team first prepare 3-D tin nanoflowers on a titanium substrate by thermal pyrolysis of dibutyltin dilaurate in a stream of ultrapure argon. The dimensions of the tin nanopetals depend on the applied temperature and the flow rate of the argon. The team then converts the tin nanoflowers to SnO₂ nanoflowers using a shape-preserving thermal oxidation process. "The preservation of the entire morphology of the nanoflowers under thermal oxidation suggests a major route for the fabrication of other 3-D metal oxide nanostructures from 3-D metal nanomaterials," Chen says.

Flame retardants in U.S. groceries

Almost every U.S. food of animal origin is contaminated with polybrominated diphenyl ethers (PBDEs), according to the first survey of PBDEs in U.S. groceries. PBDE flame retardants are used extensively in textiles, plastics, and electronics. Researchers have reported their presence in U.S. and European sediments and in human blood and breast milk. The human toxicology is not known, says Arnold Schecter, professor of environmental sciences at the University of Texas, but animal studies indicate PBDEs may be neurotoxic or carcinogenic in large doses. Schecter and coworkers hypothesized that lipid-soluble PBDEs may enter the body through ingestion of animal fats. The group sampled fish, meat, and dairy products from three national supermarket chains in Texas [Environ. Sci. Technol., published online Sept. 1, http://dx.doi.org/10.1021/es0490830]. PBDE levels varied considerably by food type, but fish showed the highest levels, followed by meat and dairy. "Absolutely, we are getting exposed to PBDEs through the diet," comments Tom A. McDonald at the California Office of Health Hazard Assessment. But he adds that the picture is fuzzy; other data point to indoor air exposure as the primary exposure route.

Building bridges bead by bead

A quick and easy method for directly forming and patterning arrays of suspended fibers has been developed by Robert W. Cohn and coworkers at the University of Louisville, in Kentucky [Nano Lett., published online Sept. 3, http://dx.doi.org/10.1021/nl048919u]. Using an array of solvated polymer droplets, the researchers dip a tiny tip--usually from an atomic force microscope cantilever or a sharpened tungsten wire--into one of the polymer beads. Once the solvent evaporates enough to give the polymer the appropriate consistency, the researchers pull the material into a second polymer bead, leaving a small, suspended bridge between the beads. The process can be continued for several minutes, moving from drop to drop until the polymer dries out. The group has also modified the technique to fabricate arrays of the suspended fibers (shown). Cohn says the arrays can be used as templates for prototype microfluidic and microoptical devices. The polymeric structures can be coated with metal or glass and then dissolved away, leaving a capillary structure behind.

SCIENCE & TECHNOLOGY ROUNDUP

John Wiley & Sons will launch a digital archive of materials science journals on Sept. 20 and of chemistry journals on Oct. 11. The most recent issues in these "backfile collections" will range in date from 1995 through 1999, depending on the journal. One-time licensing fees will be based on the size of subscribing institutions.

The first stable distannirane--a cyclopropane analog with tin atoms at two vertices of the three-membered ring and carbon at the third--has been prepared in two steps by Jean Escudié and coworkers at Université Paul Sabatier in Toulouse, France. [J. Am. Chem. Soc., published online Sept. 3, http://dx.doi.org/10.1021/ja0464239].

Jennifer A. Hollingsworth and coworkers at Los Alamos National Laboratory report the synthesis of large colloidal PbSe quantum dots that emit light in the mid-infrared wavelength region [J. Am. Chem. Soc., published online Sept. 4, http://dx.doi.org/10.1021/ja047659f]. The quantum dots are larger than 8 nm and, depending on their size, emit light over the wavelength range 2.5–4.1 µm (4,000–2,440 cm^-1). Quantum dots at these wavelengths could be useful for gas analysis, remote sensing, and atmospheric monitoring applications.