challenge. An iterative rotaxane synthesis developed by the University of Southampton’s Stephen Goldup and colleagues now allows chemists to fashion such compounds in high yield and with the ability to use different macrocycles in the same polyrotaxane (J. Am. Chem. Soc. 2016, DOI: 10.1021/jacs.6b08958). The method makes use of the copper-mediated alkyne-azide cycloaddition reaction, often referred to as click chemistry. Goldup and coworkers used a templating procedure to click together an alkyne and an azide within the cavity of a macrocycle, creating a triazole at the core of their rotaxane. Because the aromatic ring that contains the starting azide also contains a protected alkyne, the chemists are able to remove the protecting group and repeat the process over and over again. Goldup’s team made a polyrotaxane containing five of the same macrocycle moieties using this procedure, forming each new mechanical bond in 90% yield. They also used the method to thread three different kinds of macrocycle onto the same axle moiety in a specified order.—BETHANY HALFORD
GEOCHEMISTRY
CREDIT: WEIJUN ZHAO (BDBF); NAT. COMMUN. (NANOCRYSTALS)
▸ Microbes turn coal methoxy groups into methane As long as people have been mining coal, they have had to be wary of methane that comes along with it—much to the detriment of canaries prior to the development of modern gas-detection methods. The source of the methane still remains something of a mystery: Scientists believe that methanogenic microbes play a large role, but it’s not clear which compounds serve as the raw material. For at least one strain of archaea, the answer appears to be methoxylated aromatic compounds derived from lignin, reports a team led by Yoichi Kamagata and Susumu Sakata of Japan’s National Institute of Advanced Industrial Science & Technology (Science 2016, DOI: 10.1126/ science.aaf8821). The researchers found that a strain of Methermicoccus shengliensis produces methane in lab tests of more than 30 individual methoxylated compounds, as well as from coal itself. Unlike previously identified methanogenic pathways, the microbe appears to produce methane through demethylation of methoxy groups, somehow coupled to reduction of carbon dioxide and possibly involving acetyl coenzyme A as an intermediate. The microbes may also be producing methane in other subsurface
MATERIALS
Taking on an organic glow Phosphorescent materials, which continue to glow even after the light that put them into an excited state has been removed, have applications in electronics, optics, and biology. But achieving phosphorescence at room temperature and in the presence of oxygen can be tough because the excited O state of such molecules is sensitive to these conditions. To date, most compounds that exhibit O room-temperature phosphoresBDBF cence contain metals, making them more costly and potentially toxic. Chemists in China now report a series of five organic molecules that efficiently and persistently phosphoresce in a range of colors BDBF sets a new in air and at room temperature (Chem 2016, DOI: 10.1016/ precedent by j.chempr.2016.08.010). The team, led by Ben Zhong Tang of phosphorescing Hong Kong University of Science & Technology and Qian under ambient Peng of the Institute of Chemistry, Chinese Academy of conditions, Sciences, designed the aromatic carbonyl compounds so shown here that their excited states have a tunable configuration that 0.2 seconds promotes phosphorescence. The most promising comafter excitation. pound, 1-(dibenzo[b,d]furan-2-yl)phenylmethanone, or BDBF, has a phosphorescence lifetime of 230 milliseconds and an efficiency of 34.5%. The researchers hope the design guidelines they developed will lead to even better organic phosphors.—BETHANY HALFORD
sedimentary organic material, the researchers suggest.—JYLLIAN KEMSLEY
decades whether this industrial reaction for making methanol is sensitive to the structure of the copper catalyst surface or simply requires the presence of the cataCATALYSIS lytic metal. Other industrial-scale catalytic reactions fall squarely into the “structure sensitive” or “insensitive” categories, which is key information for maximizing catalyst performance. To settle the debate, Utrecht University’s Roy van den Berg, Krijn P. de Jong, and coworkers in conjunction with colleagues at catalyst manufacturer Haldor A study of a series of copper nanocrystals Topsoe synthesized 42 batches of supported confirms that their surface structures dicopper catalysts with and without zinc, a catrectly affect how well the crystals catalyze alyst promoter, in the 2- to 15-nm-diameter conversion of synthesis gas (CO + H2) to size range—a range in which crystal surface methanol (Nat. Commun. 2016, DOI: 10.1038/ structure depends strongly on crystal size. ncomms13057). Scientists have debated for The team analyzed the crystals with X-ray diffraction and electron microscopy methods and then ran a series of catalysis tests at conditions similar to those of commercial methanol processes. The group determined that regardless of the presence or absence of zinc, particles 8 nm in diameter and smaller are far less active than larger particles because the smaller Analysis of copper nanocrystals (left) with a colorparticles cannot accommocoded element map (right) indicates that size matters: date the configurations of These 7.4-nm uniformly sized particles are a tad too atoms that are catalytically small to catalyze methanol synthesis. active.—MITCH JACOBY
▸ Methanol synthesis hinges on catalyst structure
OCTOBER 17, 2014 | CEN.ACS.ORG | C&EN
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