August 20, 2007

Volume 85, Number 34

p. 50

Science & Technology Concentrates

Two-faced detergents

A new detergent with a structure that deviates from the conventional topology of amphiphilic molecules could help drug developers eke out hard-to-get structural information about membrane-bound protein targets (Angew. Chem. Int. Ed., DOI: 10.1002/anie.200701556). Detergents usually have a polar head group and a nonpolar alkyl tail, and one of their uses is mimicking cellular lipids to help preserve the structure and function of membrane proteins. To make the new detergent, a team led by Qinghai Zhang of Scripps Research Institute modified a steroid skeleton (shown, red) with polar sugar side groups (blue). The molecule's unmodified face packs against the membrane-spanning portion of a protein, leaving the side groups exposed as shown. The detergent has a larger surface area than conventional detergent molecules and can better maintain the proteins' integrity and catalytic activity than standard detergents, thus improving structural analysis, according to coauthor M. G. Finn.

Nanocomposite paper device stores energy

Carbon nanotubes, cellulose, and a room-temperature ionic liquid have been combined to create a nanocomposite paper that functions as a thin, lightweight, flexible energy-storage device (Proc. Natl. Acad. Sci. USA 2007, 104, 13574). "The paper can be rolled up, twisted, or bent to any curvature and is completely recoverable," say Victor L. Pushparaj and colleagues at Rensselaer Polytechnic Institute, Troy, N.Y. The nanotubes, nanoporous cellulose, and imidazolium-based ionic liquid serve as the electrodes, separator, and electrolyte, respectively, in an integrated nanocomposite layer. These layers can be stacked to create batteries, supercapacitors, and hybrids of these two types of devices. The researchers note that the discharge capacity and performance they observe "compare well" with figures reported for other flexible energy-storage devices. And, they add, their supercapacitors can provide a quick burst of energy over a much wider temperature range than commercial supercapacitors. The team has yet to develop a way to inexpensively mass-produce the devices, which might be used in smart cards, displays, and implantable medical devices.

Iron cluster assumes snakelike structure

Taking advantage of a little-used O,N,N,O chelating ligand, George Christou and coworkers at the University of Florida have created new iron cluster compounds, including a record-length Fe₁₈ molecular chain with an unusual structure that resembles a double-headed serpent with open jaws (Chem. Commun. 2007, 3359). Transition-metal clusters—in particular those with an iron-oxygen core—are of interest for their magnetic properties and as models for biomolecules such as the iron-storage protein ferritin. Alkoxide-based ligands such as tripodal alcohols typically have been used to connect iron atoms to make these clusters. Christou's group decided to try creating new cluster types by using an ethylenediamine ligand with hydroxyethyl arms, HO(CH₂)₂NH(CH₂)₂NH(CH₂)₂OH. One result is the Fe₁₈ cluster in which the oxygen atoms of the ligands bridge different pairs of iron atoms (Fe-O core shown) and the nitrogen atoms bind to a single iron atom. The molecule surpasses a Cr₁₂Ni₃ compound as the longest chainlike metal cluster yet discovered.

Germanium goes glassy

By applying a lot of pressure to a little germanium, C. Austen Angell of Arizona State University and an international team of collaborators have prepared the first monatomic metallic glass (Nature 2007, 448, 787). Think of glasses as frozen liquids—their constituent atoms are closely packed and randomly ordered. But since the material doesn't flow as a liquid does, it is, for all practical purposes, a solid. While a number of substances can be coaxed into a glassy state, making glasses from monatomic metals is challenging because the molten metal has a strong tendency to crystallize when cooled below its melting point. Angell and coworkers thwarted crystallization in germanium by applying 7.9 gigapascals of pressure to the molten metal during the cooling process. The pressure reduces the temperature at which the metal normally crystallizes. Atomic motion at the new crystallization temperature becomes sluggish, and the germanium retains the disorder of its liquid phase as it solidifies.

Cats as canaries for thyroid disease

Hyperthyroidism is a leading cause of illness in cats, and the first reports of the feline disease in the late 1970s coincided with the first reports of environmental contamination arising from polybrominated diphenyl ethers (PBDEs), which are used as flame retardants in household products such as carpeting and televisions. Structural similarities between some PBDEs and the hormone thyroxine, along with toxicological studies, have led researchers to suspect a link between PBDEs and thyroid dysfunction. In a new study, a team led by EPA's Janice A. Dye reports that blood PBDE levels in cats are 20 to 100 times greater than those of adult humans (Environ. Sci. Technol., DOI: 10.1021/es0708159). The researchers hypothesize that the elevated PBDE levels stem from canned cat food (primarily fish) and PBDE-laden household dust ingested while grooming. They propose that cats could be sentinels—akin to canaries in coal mines—for human thyroid problems associated with chronic PBDE exposure.

Chemical & Engineering News

ISSN 0009-2347

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