Tube hybrids transport electrons
With their extended, delocalized -electron systems, single-walled carbon nanotubes (SWNTs) seem like ideal charge transporters for nanotechnological applications. However, scientists have had to take fairly complicated approaches to exploit the tubes’ charge-transporting abilities. Now, Dirk M. Guldi of the University of Erlangen, in Germany, and coworkers have developed a simple, supramolecular approach that transforms SWNTs into electron donor-acceptor nanohybrids but still leaves the pristine nanotubes intact [Angew. Chem. Int. Ed., 43, 5526 (2004)]. Guldi’s system (shown) works by coordinating pyrene molecules to the SWNT surface through -stacking interactions. The pyrene has a positively charged trimethylammonium acetyl sidearm that coordinates with the system’s third component-a negatively charged porphyrin complex-via electrostatics. When the researchers photoexcite this assembly, they rapidly generate a charge-separated state that has a microsecond lifetime. Guldi believes the approach could have applications in photovoltaics.
Researchers have developed a way to examine the elemental composition of single bacterial cells using high-energy X-ray fluorescence. Kenneth M. Kemner of Argonne National Laboratory and coworkers show that their noninvasive, nondestructive technique can be used to make elemental maps of living cells with spatial resolution of 150 nm [Science, 306, 686 (2004)]. As a demonstration, Kemner’s team mapped the elemental composition of single cells of a type of aquatic bacteria that naturally lives either in water or in complex, surface-adhered communities called biofilms. The researchers show that the elemental composition of bacteria that drift differs markedly from that of bacteria that are adhered to a substrate. In particular, the attached cells boast elevated levels of calcium and phosphate, which Kemner suggests may stem from the apatite-mineral cocoon with which surface-adhered bacteria surround themselves. Kemner says the technique-which can also be used to probe the redox state of specific metals-will prove particularly useful for dissecting the role bacteria play in geology.
Membrane proteins have been difficult to study with electrospray mass spectrometry because protein-lipid interactions are lost under the conditions needed for protein solubility. Carol V. Robinson and her coworkers at the University of Cambridge chemistry department and the MRC Laboratory of Molecular Biology show that they can use electrospray MS of protein-micelle complexes as a model system to study drug binding to membrane proteins [J. Am. Chem. Soc., published online Oct. 14, http://dx.doi.org/10.1021/ja0450307]. They obtain electrospray mass spectra of the small cation tetraphenylphosphonium bound to an Escherichia coli membrane protein involved in multidrug transport that’s been embedded in micelles of the detergent dodecylmaltoside. The resulting mass spectrum contains broad peaks of overlapping species. The researchers extract information with tandem MS by isolating narrow “windows” at high mass-to-charge ratio values and building a complete spectrum of the overlapping species. “This is the first time we are aware of that a protein-micelle complex has been observed to remain intact by mass spectrometry,” Robinson says. “It opens up a new field of research for directly assessing [the binding of] specific drugs” to membrane proteins.
Methane can be converted to higher hydrocarbons at relatively low temperature using a heterogeneous catalyst developed by researchers in France. Jean-Marie Basset, Daravong Soulivong, and Christophe Copéret at the French National Center for Scientific Research (CNRS) and the University of Chemistry, Physics & Electronics in Lyon and their coworkers at BP Chemicals have shown that an electrophilic tantalum hydride catalyst supported on silica facilitates alkane metathesis reactions. Prepared using surface organometallic methods, the new catalyst demonstrated its usefulness in a test reaction in which a mixture of methane and propane was converted to ethane with nearly 100% selectivity at 250 °C [Angew. Chem. Int. Ed., 43, 5366 (2004)]. The study shows that methane can be used in place of hydrogen to cleave carbon-carbon bonds, which may lead to cost savings and environmental benefits. In addition, the new catalyst may provide a long-sought method for direct conversion of methane, which is abundant in natural gas yet relatively unreactive, to more valuable products.
Chemists have packed more punch into a tuberculosis antibacterial by giving it its own drug. Ethionamide (shown) is a prodrug activated by Mycobacterium tuberculosis’ own enzyme, EthA, and transcription of EthA’s gene is repressed by the protein EthR. Because EthR’s activity prevents activation of ethionamide, the antibacterial must be dosed at almost toxic levels. Research scientists Alain R. Baulard and Vincent Villeret at the Pasteur Institute, in Lille, France, and their colleagues crystallized EthR in the presence of an inhibitor [Mol. Cell, 16, 301 (2004)]. Then, they dropped a related inhibitor-benzylacetone-into a mix of bacteria and ethionamide. The EthR inhibitor made ethionamide effective at one-third its normal dose. (Benzylacetone itself is powerless as an antibacterial.) Baulard says that the strategy of using an EthR inhibitor to enhance ethionamide activity may well be used to fight leprosy bacteria, too. Plus, the more general strategy of using one drug to enhance another could be applied to many prodrugs.