SCIENCE & TECHNOLOGY CONCENTRATES
WATER SPLITTING: ADVANCING OXIDATION ... Solar fuels can be made by splitting water into H2 and O2 with the help of sunlight. Most photosynthetic organisms use a manganese-centered structure known as photosystem II for the O2 evolution portion of that process. But the most active synthetic mimics of that system break down quickly under catalytic conditions as the catalyst molecules react with one another to form a variety of inert species. Siddhartha Das and Binod Nepal of Utah State University have now found a way to keep the catalyst molecules apart by assembling them inside the pores of a metal-organic framework (MOF), like a ship in a bottle (Angew. Chem. Int. Ed. 2013, DOI: 10.1002/anie.201301327). The team prepared the system by floating the reactants into the MOF sequentially. Their assembled Mn unit is too large to diffuse out the way its components came in, or to diffuse between neighboring chambers. The resulting MOF-catalyst system, constructed entirely from Earth-abundant elements, sustains water oxidation for more than seven hours with no signs of slowing. The same catalyst without the MOF cage produces O2 twice as fast but lasts less than seven minutes. The group now hopes to develop a photoactive MOF to make the reaction self-contained and solar-driven.—CB
... AND HYDROGEN EVOLUTION
J. AM. CHEM. SOC.
Hydrogen’s appeal as an environmentally friendly fuel and energy carrier is heightened by the tantalizing possibility of obtaining the lightweight gas by splitting water. The final step in that process, the hydrogen evolution reaction (HER), reduces and combines hydrogen ions to form H2. Platinum is a top-notch HER catalyst, but it is expensive. The search for low-cost alternatives recently turned up MoS2, an unexpected but promising candidate. Now, chemists at the University of Wisconsin, Madison, report a simple chemical process that transforms MoS2 from a semiconduct-
BPA THROUGH ORAL ROUTE REMAINS ACTIVE Experiments with dogs have found that the controversial chemical bisphenol A (BPA) can be absorbed under the tongue and pass directly into the bloodstream. Proof of this exposure route, not shown conclusively until now, suggests that higher levels of BPA may persist in the body than previously thought and be available to do harm (Environ. Health Perspect. 2013, DOI: 10.1289/ehp.1206339). BPA is a synthetic building block used to make the polycarbonate plastics and epoxy resins used in food containers and a host of other products. Animal studies have shown that BPA mimics the action of hormones and that the trace amounts that people are exposed to may be contributing to health problems such as diabetes and heart disease. But the human health risk from BPA exposure remains murky because of uncertainty in how it enters the bloodstream. During digestion, BPA passes through the gastrointestinal tract and is metabolized in the liver. Via that route, most BPA is conjugated to glucuronic acid to create an inactive species that is excreted. Animal studies to test BPA and other chemicals tend to use feeding tubes or other methods to control the dose, an approach that bypasses direct absorption through the mouth. A research team led by Pierre-Louis Toutain at Toxalim Research Centre in Food Toxicology, in Toulouse, France, administered BPA to dogs by mouth, by feeding tube, and intravenously and found that BPA absorption under the tongue leads to the highest levels of unmetabolized BPA in the blood. The researchers believe their findings will have “major implications” in interpreting human biomonitoring data and making chemical risk assessments.—SR
ing phase to a metallic one and significantly enhances its performance as an HER catalyst (J. Am. Chem. Soc. 2013, DOI: 10.1021/ ja404523s). Mark A. Lukowski, Song Jin, and coworkers used standard chemical vapor deposition methods to grow semiconducting MoS2 on graphite. By treating the product with n-butyllithium and water, they produced A simple chemical exfoliated metallic method exfoliates MoS nanosheets. 2 MoS2, as seen in Electrocatalysis and this SEM image, other tests show that, and boosts its catalytic activity. compared with the starting material, the nanosheets expose a higher density of HER active sites, mediate faster electrode kinetics, and enhance electronic conductivity. This simple method of altering nanostructures may be useful in modifying other layered materials to enhance their properties, the team suggests.—MJ CEN.ACS.ORG
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ANTHRAX SLAYER FROM THE DEEP To fight anthrax infections, patients must often endure a prolonged course of antibiotics, with treatment lasting up H to six months. Because the H bacterium that causes this infection, Bacillus anH H thracis, has been used O O as a bioterrorism agent, scientists O O H have been vigilant about seeking betAnthracimycin ter anthrax antibiotics. Now, chemists led by William Fenical of the University of California, San Diego, and Scripps Institution of Oceanography have found one. In marine sediments off the California coast, Fenical’s team identified a bacterium and extracted compounds from it. One proved to be a potent killer of both B. anthracis and methicillin-resistant Staphylococcus aureus, another deadly bacterium (Angew. Chem. Int. Ed. 2013, DOI: 10.1002/anie.201302749). The researchers isolated and determined the structure of the compound responsible for the antibiotic activity, naming it anthracimycin.
SCIENCE & TECHNOLOGY CONCENTRATES
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EASY ROUTE TO CONDUCTIVE NANOSHEETS The class of materials called metal dichalcogenides—which includes compounds such as MoS2, WSe2, and TaS2—finds use in numerous high-tech applications. Examples include transistors, capacitors, batteries, catalysts, and hydrogen storage materials. Nanostructured versions of these compounds can be more stable chemically and exhibit better electronic properties than their bulk counterparts. They might find even broader applications if they weren’t typically prepared via laborious methods such as sputtering, chemical vapor deposition, and electrodeposition. University of Southern California chemists may have come up with an attractive solution. Priscilla D. Antunez, A simple solutionDavid H. Webber, phase method and Richard L. yields high-quality Brutchey have dem- nanosheets of WSe2 onstrated a simple (W is white; Se is solution-phase yellow) method to prepare highly conductive WSe2 nanosheets (Chem. Mater. 2013, DOI: 10.1021/cm400790z). The team reacted di-tert-butyl diselenide with WCl4 in dodecylamine and treated the product with a surfactant to prevent the crystallites from agglomerating. The group reports that the high-yield method produces “phase pure” samples that exhibit conductivity values typical of samples prepared by painstaking methods.—MJ
COPPER ENABLES DIRECT AROMATIC FLUORINATIONS Using a copper catalyst and directing groups, chemists have devised a versatile reaction that adds one or two fluorine
N HN
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P. McElroy of the University of Dundee, F F in Scotland, and coworkers find that the assay used to identify ataluren as a readthrough agent gave a false-positive indication, because it interacts with CO2CH3 CO2CH3 the assay’s luciferase reporter enzyme atoms to selected positions on aromatic instead of the protein translation prorings (J. Am. Chem. Soc. 2013, DOI: 10.1021/ cess (PLoS Biol. 2013, DOI: 10.1371/journal. ja4047125). The development adds to repbio.1001593). McElroy’s team used cent advances in organofluorine chemistry other assays to show that ataluren has no that are making it easier for chemists to readthrough activity, suggesting that any synthesize pharmaceuticals, agrochemiefficacy it has is the result of some other cals, and radiolabeled agents for medical bioactivity. PTC Therapeutics maintains imaging applications. Thanh Truong, that ataluren readthrough has also been Kristine Klimovica, and Olafs Daugulis confirmed in nonluciferase assays and of the University of Houston developed that it shows activity in cells, animals, and the procedure by building on earlier work people.—SB by the Daugulis group for palladium- and copper-catalyzed ortho C–H activation A POTENT STEP TOWARD and functionalization of aromatic rings. Key to those selective reactions was using BANISHING HIV bidentate aminoquinoline or picolinamide directing groups on the arBy subtly tweaking the structure of the omatic substrate. Daugulis natural product prostratin, chemists have and coworkers reasoned come up with molecules that could help that similar chemistry eradicate AIDS (Proc. Natl. Acad. should work for directed Sci. USA 2013, DOI: 10.1073/ O fluorinations. They show pnas.1302634110). The curthat selective fluorination rent antiretroviral cocktail O of benzamides (shown) used to treat HIV and benzylamides can be only attacks active H accomplished by using virus. People copper iodide as the catamust take OH lyst and silver fluoride as these drugs OH the fluorine source under for life because O OH oxidizing conditions. The the virus also Prostratin analog ability to add one or two fluorine atoms adopts a dormant to the aromatic ring can be controlled by provirus form, which hides in immune altering the amount of catalyst and the recells and can emerge as active virus. Ceragent ratios.—SR tain natural products, such as prostratin, can coax dormant provirus out of hiding. By using such compounds, doctors could DRUG CANDIDATE’S flush HIV from a patient’s system and efMECHANISM IN QUESTION fectively cure the disease. Paul A. Wender of Stanford University, Tae-Wook Chun An experimental drug in human cliniof the National Institutes of Health, and cal trials for muscular dystrophy doesn’t Jerome A. Zack of the University of Caliwork in the way scientists had originally fornia, Los Angeles, have come up with proposed, a study finds. In 2007, PTC prostratin analogs that are more potent Therapeutics developed the small molthan the parent compound. The molecules ecule ataluren as a readthrough agent, a can be made in seven steps from phorbol, molecule that restores protein levels in a component of croton oil, which comes cells with mutations that block production from the seeds of a tropical shrub. At of those proteins. In cells and in mice with nanomolar concentrations, one of the a muscular dystrophy mutation, ataluren compounds (shown) ferreted the virus boosts levels of the disease-related protein out of immune cells from HIV-positive and improves muscle function, respecpatients taking the antriretroviral cocktail. tively. Ataluren is in a Phase III trial for It took 100 times as much prostratin, curmuscular dystrophy, and a cystic fibrosis rently a preclinical drug candidate, to do trial is planned. In the new study, Stuart the same job.—BH CuI, AgF, oxidant
CHEM. MATER.
Anthracimycin has an unusual structure, with a fused ring system and an enolized β-diketone. The researchers believe that the anthracimycin structure may represent an important new class of bacteria-fighting compounds.—BH
CEN.ACS.ORG
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