Issue Date: March 8, 2004
Nanovalve opens on demand
By tethering a pseudorotaxane to a nanopore, chemists at the University of California, Los Angeles, have created a working supramolecular nanovalve [J. Am. Chem. Soc., published online, Feb. 28, http://dx.doi.org/10.1021/ja039424u]. The group, led by chemistry professors J. Fraser Stoddart and Jeffrey I. Zink, constructs the valves by first preparing 2-nm-diameter nanopores equipped with pseudorotaxane tethers (red rods in the graphic shown) on a thin film and filling the pores with fluorescent molecules (yellow spheres). They then use noncovalent interactions to thread bulky, redox-sensitive cyclobis(paraquat-p-phenylene) moieties (blue squares) over the tethers, effectively capping the tiny containers. Adding a reducing agent disrupts those interactions, unthreading the pseudorotaxane so that the valve opens and releases the pore's contents. The researchers say these molecular devices could be used to dispense drugs and enzymes.
Tabletop fusion bubbles along
Researchers who published a controversial Science paper in 2002 suggesting that nuclear fusion was occurring in an inexpensive tabletop apparatus now report additional evidence for the effect. In work to be published this month in Physical Review E, Purdue University nuclear engineering professor Rusi P. Taleyarkhan and coworkers describe improvements to their experiments and additional data in response to critical comments on the original paper. The researchers bombard deuterated acetone in a liter-sized reaction cell with ultrasound and pulses of 14-MeV neutrons, which generates tiny, vapor-filled bubbles that greatly expand and contract. Upon collapse of the bubbles, extremely high temperature and pressure occurs within them--conditions amenable for fusion. The researchers report expected flashes of light (sonoluminescence) from the bubbles and emission of 2.45-MeV neutrons, tritium, and γ-rays that are telltale signs of deuterium fusion. Taleyarkhan plans to scale up the device, which could be used as a neutron source or to produce tritium. The process still doesn't generate more energy than it consumes, but Taleyarkhan believes that might yet be possible. Several of the original report's critics continue to express concerns about the results.
Grumblings about Gaussian
Bitterness among some chemists who claim the licensing terms of the popular commercial quantum chemistry software Gaussian are unfair has prompted them to post a website, http://www.bannedbygaussian.org, in protest. Scientists who develop competing programs, such as Jaguar or GAMESS, are forbidden to use Gaussian. This makes it difficult for Gaussian users to collaborate with these scientists, particularly in cases where computers are shared by many groups, they say. The license terms also forbid users from publishing data comparing Gaussian performance with other software programs. "This is bad for science," says Mark S. Gordon, chemistry professor at Iowa State University, Ames. Michael J. Frisch, president of Gaussian Inc., which sells the software, calls the website "a collection of half-truths and misstatements." The Gaussian issue has been simmering for years, highlighting a growing conflict between academic freedom and business interests.
Resin scavenges, indicates amines
A novel dual-function resin not only removes amine from solution but also indicates its presence. The polystyrene resin (shown) is bound to bromophenol blue--a dye that is blue in the presence of amines--and two methylisocyanate groups that scavenge amines. Mark Bradley, a chemistry professor at the University of Southampton, in England, and coworkers showed that the self-indicating resin can be used for in situ reaction monitoring and purification during the preparation of a small, solution-phase combinatorial library of ureas [Chem. Commun., 2004, 502]. The team synthesized the array of ureas by the reaction of six amines with three isocyanates and one isothiocyanate. When self-indicating resin is added to the library, its color changes from blue to yellow as it removes excess amine from the solutions. All the reactions give high purities of ureas, even in cases where yields were not so high. "This approach allows the visual inspection of the completeness or otherwise of parallel arrays of reactions in a manner previously impossible," Bradley says.
Boost for membrane protein analysis
Identification and quantification of integral membrane proteins overexpressed in particular diseases could provide new targets for drug design. Unfortunately, proteomic analysis of these proteins, which extend into the cell membrane, is notoriously challenging because of their hydrophobic nature and the difficulty of preparing a clean plasma membrane fraction. Biochemist Yingming Zhao and coworkers at the University of Texas Southwestern Medical Center describe a method to enrich these proteins [Anal. Chem., published online Feb. 28, http://dx.doi.org/10.1021/ac0354037]. They isolate biotinylated plasma membrane sheets using biotin-streptavidin affinity enrichment. Cytosolic proteins are removed by washing the fraction with high-salt and high-pH buffers. The integral membrane proteins are then extracted and resolved by gel electrophoresis and analyzed. Using a 30-mg sample, they identified 898 proteins, 781 of which could be annotated with regard to subcellular localization. Of those, at least 526 were integral membrane proteins. The method can be integrated with a protein quantification method to discover membrane proteins overexpressed in disease cells.
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