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Science & Technology

May 5, 2008
Volume 86, Number 18
pp. 38-39

Science & Technology Concentrates

Microfluidic spider silk

Sebastian Rammensee

How a spider's spinning duct turns protein solutions into threads as strong as steel is still largely a mystery. But German scientists have now designed a microfluidic device (shown) to serve as an artificial spinning duct (Proc. Natl. Acad. Sci. USA 2008, 105, 6590). The device allows precise control over conditions such as ion concentration and pH that are believed to be critical for silk formation. Led by Thomas Scheibel at the University of Bayreuth and Andreas R. Bausch at the Technical University of Munich, the researchers worked with two components of the dragline silk used to make a spiderweb's outer rim and spokes. They found that one protein, eADF4, would not make fibers on its own and instead aggregated into solid protein spheres. The other protein, eADF3, formed fibers, but only at pH 6 and high phosphate concentration and with accelerated flow through the device. A mixture of the two proteins also yielded fibers. The results point toward a model for silk formation in which the proteins form colloidal intermediates before assembling into fibers, the authors say.

Firing up the tank with nanoparticles

In an attempt to make liquid fuels more energy efficient, scientists have found that adding aluminum or aluminum oxide nanoparticles to diesel fuel improves its ignition properties (Nano Lett., DOI: 10.1021/nl080277d). In simple hot-plate experiments, Arizona State University mechanical engineer Patrick E. Phelan and coworkers found that diesel fuel containing 0.1% aluminum or aluminum oxide nanoparticles ignites more readily at lower temperatures than pure diesel. The researchers suspect that adding nanoparticles to diesel improves the fuel's radiative properties and its heat- and mass-transfer capabilities. The nanoparticles increase the probability that a single drop of the fuel will ignite at just above 700 ÂșC. The probability increases from about 15% for pure diesel to between 50 and 60% for nanoparticle-enriched diesel. Phelan's group also looked at two different sizes of Al2O3 particles and found that 50-nm particles were slightly better at getting diesel to ignite than 15-nm particles but only at the lower range of temperatures tested. Envirox, a cerium oxide-based catalyst nanoparticle that's reported to boost fuel efficiency, is already on the market from nanomaterials firm Oxonica.

Oligogermanes start to branch out

The periodic table foretells that the chemistry of germanium should be similar to that of carbon. Indeed, a growing number of linear oligogermanes are being synthesized. These are compounds with germanium backbones and hydrocarbon substituents that are the closest germanium analogs to linear hydrocarbons. But reports of branched oligogermanes are rare. Monika L. Amadoruge and Charles S. Weinert at Oklahoma State University and coworkers now report a novel stepwise strategy for constructing branched oligogermanes that could change that situation (Organometallics, DOI: 10.1021/om800040f). In one example, the researchers reacted PhGeH3 with three equivalents of Ph3GeN(CH3)2 in acetonitrile solution to make the tetragermane PhGe(GePh3)3, where Ph = phenyl. The chemists obtained the crystal structure for this compound (shown), which is a first for a branched oligogermane. The team also prepared PhGe(GeBu2H)3, where Bu = butyl, and used it as a building block to construct more highly branched heptagermanes. The germanium atoms impart to these compounds potentially useful optical and electronic properties that differ from those of their hydrocarbon relatives, the researchers note. They are in the process of constructing larger dendrimer-like oligogermanes, and "we have developed a method to include chiral Ge centers into the Ge–Ge backbones," Weinert says.

Semiconductors via combustion

Combustion synthesis is a low-cost, low-tech, and energy-efficient preparation method that can be used to synthesize nanocrystalline tungsten trioxide, an important inorganic oxide semiconductor, according to Krishnan Rajeshwar, Norma R. de Tacconi, and coworkers at the University of Texas, Arlington (J. Am. Chem. Soc., DOI: 10.1021/ja8012402). Inorganic oxides such as WO3 and TiO2 are widely used in photovoltaic devices, in photocatalytic generation of hydrogen from water, and in related applications. Tungsten trioxide typically is synthesized in a variety of forms via chemical vapor deposition, electron-beam evaporation, and other high-tech procedures. Rather than using those methods, the UT Arlington team prepared the oxide by combusting a peroxopolytungstic acid derivative with compounds such as glycine, urea, and thiourea, which function as fuels. The researchers report that the particles of the combustion products tend to be three to four times smaller (10- to 20-nm diameter) and exhibit a lower band gap than commercial samples of WO3. The band gap, an optoelectronic property that depends on "dopant" atoms originating in the fuel, can be tailored to broaden the spectrum of sunlight that can be absorbed by WO3, the team says.

Getting stuffed improves stability of boron fullerenes

Adding to the growing theoretical collection of boron analogs of fullerenes, chemists have postulated that a new family of boron clusters stuffed with a few extra boron atoms should be more stable than the previously hypothesized champion of stability, B80. Because boron in many ways resembles carbon in its properties—except in having one fewer electron—chemists have long been intrigued by the possibilities of creating graphitelike and fullerene-like boron materials. Chemists are still working out how to make the compounds, so most research in the area is done on a computer. Eluvathingal D. Jemmis at the Indian Institute of Science, in Bangalore, India, and colleagues used density functional theory to determine the electronic structure and geometries of buckyball-esque boron clusters (Phys. Rev. Lett. 2008, 100, 165504). Their clusters are built upon a base unit of B84, rather than B80. B84 is a ball-shaped framework with an icosahedral B12 unit inserted in the middle. The B84 model has the same symmetry as the C60 fullerene, but B84 requires 50 more electrons to make it stable. By distributing additional boron atoms at various sites around the B84 molecule, the authors found several configurations—from B98 to B102—that are predicted to have greater stability than B80.

Souped-up nanomotors

Drop a bimetal nanowire, composed of a segment of gold and a segment of platinum, into a solution of aqueous hydrogen peroxide and the tiny rod will chug along at about 8 μm/second. These catalytic nanomotors propel themselves because the platinum segment catalyzes the decomposition of hydrogen peroxide; the resulting oxygen provides thrust to drive the nanowire through the solution. By incorporating carbon nanotubes into the platinum end of the nanowires, Joseph Wang, Rawiwan Laocharoensuk, and Jared Burdick of Arizona State University have managed to get a nanomotor to zip around at about 50 μm/second, a speed that approaches that of biomolecular motors, such as kinesin (ACS Nano, DOI: 10.1021/nn800154g). According to the researchers, the nanotubes enhance the decomposition reaction, generating more oxygen and, consequently, providing a speed boost. Adding hydrazine to the hydrogen peroxide gives the nanomotors even more oomph, making them zoom along at 200 μm/second in some cases. "We expect that the development of highly efficient and controllable nanomotors will open the door to powerful nanovehicle systems performing diverse operations of increasing complexity," the researchers write.

John Boland/Trinity College Dublin
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How to dissolve your carbon nanotubes

Although carbon nanotubes are generally regarded as insoluble in all solvents, a research team led by Jonathan N. Coleman of Trinity College Dublin and James P. Hamilton of the University of Wisconsin, Platteville, has found that carbon nanotubes actually can be dissolved in N-methylpyrrolidone (NMP) and other solvents with a surface energy that matches that of graphitic surfaces (Adv. Mater., DOI: 10.1002/adma.200702451). The investigation may eventually enable researchers to process carbon nanotubes conveniently via ink-jet printing and other procedures suitable for soluble polymers. Because of carbon nanotubes' extreme insolubility, they are typically chemically modified to enable their dispersion in various liquids, including NMP. On the basis of spectroscopy and scanning-probe measurements, the team finds that nanotube bundles in NMP spontaneously exfoliate (unpeel) upon dilution and that NMP molecules adsorb (shown on top) and desorb (bottom) reversibly to the nanotubes—a key step toward dissolution. The scientists also find that the nanotube-NMP interaction is characterized by a negative enthalpy of mixing, which indicates "solubility in the classical thermodynamic sense, like sugar in water or polystyrene in acetone," Hamilton says.

Seawater boosts tomato's antioxidants

Riccardo Izzo

Irrigating cherry tomatoes with diluted seawater produces tastier fruit with increased antioxidant levels, according to a new study (J. Agric. Food Chem., DOI: 10.1021/jf0733012). Numerous studies have linked antioxidants found in tomatoes to health benefits, such as protection against heart disease and some cancers. And although tomatoes grown in saline conditions are known to be smaller, researchers know little about how salt affects a tomato's nutritional content. Riccardo Izzo, Cristina Sgherri, and colleagues at the University of Pisa, in Italy, grew cherry tomatoes in a greenhouse with freshwater or 12% diluted seawater. Using liquid chromatography, the researchers found that the cherry tomato grown with saltwater (shown) contained more sugar (37%) and higher levels of antioxidant compounds such as vitamin C (20%), vitamin E (20%), dihydrolipoic acid (31%), and chlorogenic acids (15%) than the same variety irrigated with freshwater. The ability to grow tomatoes in salty water could be important in arid climates with limited freshwater, the authors note, but they caution that repeated use of even dilute seawater could harm soil quality.

Chemical & Engineering News
ISSN 0009-2347
Copyright © 2008 American Chemical Society


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