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Transparent semiconductor has magnetic appeal
Imagine a material with the semiconducting properties needed for electronic devices, the ferromagnetism useful for information storage, and the transparency essential for fabricating display screens. A team of researchers in Japan has found transition-metal-doped titanium dioxide to be just such a material. "Rather serendipitous" results from combinatorial synthesis experiments led Hideomi Koinuma, professor of materials chemistry at Tokyo Institute of Technology, and coworkers to thin films of cobalt-doped anatase (Ti1- xCoxO2). The films are colorless, transparent semiconductors exhibiting ferromagnetism "even at room temperature" [Science, published Jan. 12, Science Express, http://www.sciencemag.org/sciencexpress/recent.dtl]. The researchers aren't sure what makes the material magnetic, but they argue that X-ray diffraction and transmission electron microscopy studies rule out the possibility that cobalt clusters could be responsible.
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Microchannel fluids moved electrically
Scientists in the Nether-lands have used electrocapillary pressure (ECP) to manipulate fluids in 3-D structures having thousands of microchannels [Science, 291, 277 (2001)]. Physicist Menno W. J. Prins and coworkers at Philips Research, Eindhoven, coated the microchannel walls with an aluminum conducting layer, an insulating layer, and a hydrophobic fluoropolymer top layer. The team filled the microchannels with two immiscible fluids: an electrically conducting aqueous solution and an electrically insulating gas or nonpolar oil. By application of a voltage between the aluminum electrode and the aqueous fluid, the fluids could be reversibly displaced with velocities nearly two orders of magnitude higher than those achieved with other electrofluidic actuation techniques. Microfluidic manipulation by ECP relies on electrostatic control of the solid/fluid interfacial tension that arises from the electrical charge density accumulated at the interface. "In present-day lab-on-a-chip devices, the motion of fluids is controlled by tuning the channel dimensions and by external pumps," Prins explains. "With ECP technology, much more accurate, complex, and flexible chips become feasible. Other potential applications include ink-jet printers, optical switches, and radiation filters."
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| Catalyst for resolving racemic amines |
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The compound shown has just the right reactivity for catalytic kinetic resolution of racemic primary amines. Chemists Shigeru Arai, Stéphane Bellemin-Laponnaz, and Gregory C. Fu at Massachusetts Institute of Technology find that, in the presence of a chiral catalyst derived from 4-pyrrolidinopyridine and this O-acylated azlactone, racemic primary amines are acylated with selectivity factors up to 27. That means the fast-reacting enantiomer is acylated 27 times more rapidly than the slow-reacting one [Angew. Chem. Int. Ed., 40, 234 (2001)]. Fu says previous attempts at nonenzymatic catalytic kinetic resolution of amines have failed because the acylating agents that have been used react directly with the amine without the intervention of the chiral catalyst. This azlactone derivative, however, reacts more rapidly with the catalyst than with the amine, allowing the catalyst to exert its chiral influence before the reaction is completed. |
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Designed protein blocks HIV infection
A small protein designed to bind to a key protein in the virus that causes AIDS potently inhibits the virus's ability to infect cells in test-tube experiments. As such, it may serve as the prototype for a new class of drugs against HIV and perhaps other viruses as well, its developers suggest [Science, published Jan. 12, Science Express, http://www.sciencemag.org/sciencexpress/recent.dtl]. Peter S. Kim and colleagues at the Whitehead Institute for Biomedical Research and MIT designed a protein consisting of five a-helices tightly bundled together, which they anticipated would bind tightly to a sixth helix located at the carboxyl-terminal end of the viral protein gp41. HIV and many other viruses normally form such a six-helix bundle as a preliminary step to fusing with the membrane of a cell to be infected. The researchers reasoned that their five-helix protein would effectively block the virus from forming this bundle and thereby stop it from infecting new cells. The protein is effective against a wide range of HIV-1 strains, the researchers note.
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Bacterial protein interactions
The first large-scale demonstration of a promising technique for mapping interactions among an organism's proteins was reported last week by Pierre Legrain, vice president of science and technology at Paris-based Hybrigenics S.A., and coworkers [Nature, 409, 211 (2001)]. According to the researchers, their "library" method of yeast two-hybrid screening improves on the traditional "matrix" approach by permitting a reliability score to be obtained on every protein-protein interaction, by its ability to dramatically reduce false-positive and false-negative results, and by making it possible to identify the specific protein domain participating in each interaction. By screening only 261 Helicobacter pylori proteins against a library of genomically encoded peptide fragments, Legrain and coworkers identified 1,200 interactions among 47% of the bacterium's complete set of proteins. In all, about 5 billion potential interactions were assessed in the course of the procedure.
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