DNA ROBOTS DETECT BLOOD CELL TYPES
THE SOUND OF SPECTRA
Different types of immune cells in the blood can be recognized for diagnostic and therapeutic purposes by the glycoprotein markers on their surface. For example, B cells typically express the markers CD45 and CD20, whereas T cells have CD45 and CD3. In a new recognition approach— developed by Sergei Rudchenko of the Hospital for Special Surgery in New York City, Milan N. Stojanovic of Columbia University, and coworkers—a set of molecular robots made of double-stranded DNAantibody conjugates undergo molecular cascades when they bind to particular combinations of cell-surface markers (Nat. Nanotechnol. 2013, DOI: 10.1038/nnano.2013.142). After a combination of robots binds to a cell surface, adding the right single-stranded DNA molecule triggers a cascade of strand displacement reactions. Each reaction starts with an incoming strand binding to a short overhanging sequence and replacing the existing strand to form a new pair of oligonucleotides with a longer complementary sequence than the previous pair. The last reaction in the cascade unveils a molecular label that gives off a fluorescent signal, which is revealed only if the cascade runs to completion. The researchers used the DNA robots to identify groups of cells that express particular combinations of two or three cell markers.—CHA
The marimba is rarely called for when analyzing chemical data. But it is the instrument of choice for a team of educators who have adapted infrared spectra into an audio format for use by visually impaired scientists and students (J. Chem. Educ. 2013, DOI: 10.1021/ed4000124). Florbela Pereira, Joao Aires-de-Sousa, and coworkers at the New University of Lisbon used open-source Transmittance O software—available on O–H C=O 0.8 HO their MOLInsight project page—to convert IR 0.6 data to MIDI format, a type of digital music file. The magnitude of the IR peaks, normally the y axis in spectra, 0.4 is represented by the pitch, with a 0.2 higher note indicating a stronger signal. The frequency, normally the 2,000 1,000 3,000 x axis, is represented by time. After Wavenumber, cm–1 some training, a group of visually Early in the audio version of this spectrum, impaired students were able to corthe O–H stretch of butanoic acid can be rectly identify the main functional heard. A little later, the C=O stretch is groups represented in sample spec- distinguishable, followed by a variety of tra and use that information to iden- peaks in the spectrum’s fingerprint region. tify organic molecules. The software could be easily extended to other types of spectra. One student, Sérgio Neves, says the approach “allows me to summarize the spectral data into a small audio graphic, providing a more global overview of the spectrum.”—CB AUDIO ONLINE
To hear the spectral sound of butanoic acid and other samples, go to http://cenm.ag/sirs.
S HUTTERSTOCK
of the Technical University of Cartagena, in Spain, and her colleagues recruited seven men to participate in an intense stationWATERMELON JUICE ary cycling test on three separate days. Before each test, the participants drank a FOR SORE MUSCLES half-liter of one of three beverages: natural Competitive athletes often swallow amino watermelon juice containing about 1 g of acid supplements to boost their perforl-citrulline, watermelon juice enriched to mance and aid recovery from muscle have 6 g of l-citrulline, or a fruity placebo fatigue. For the amino acid l-citrulline, a drink without watermelon or l-citrulline. better way to reap its benWhen the team monitored O O efits may be to partake of a the athletes’ lactate levels in natural source—watermelblood during exercise, they H2N N OH H ons. A small study shows found no differences due to NH2 that drinking watermelon the beverages they imbibed. L-Citrulline juice before a bout of hard The day after drinking either exercise helps prevent watermelon juice, however, muscle soreness the next day the men reported essentially more effectively than a plano leg soreness. But the day cebo beverage (J. Agric. Food after drinking the placebo, Chem. 2013, DOI: 10.1021/ they reported feeling sore. jf400964r). Encarna Aguayo Aguayo is now determining the optimal concentration of l-citrulline in watermelon Watermelon juice, which juice that might help prevent contains l-citrulline, could be the next trendy sports drink. muscle fatigue.—JNC CEN.ACS.ORG
30
AUGUST 5, 2013
POPPING OFF POLLUTANTS By stitching a cyclic aluminum complex into the framework of a porous organic polymer, called a POP, researchers have created a highly catalytic, recyclable material designed to break down toxic pollutants into innocuous products. The secret to the material’s success is additional processing with supercritical carbon dioxide (J. Am. Chem. Soc. 2013, DOI: 10.1021/ ja405495u). A team of Northwestern University chemists led by Omar K. Farha, Joseph T. Hupp, and SonBinh T. Nguyen used a cobalt-catalyzed cross-coupling polymerization method to link terminal alkyne units on an aluminum porphyrin ring with alkyne units on a tetraphenylmethane building block. The researchers then treated the porphyrin-derived porous organic polymer—a PPOP—with supercritical CO2 to fluff up the flexible framework material and enhance its total porosity. The treatment, in contrast to the vacuum-heating activation process normally carried out for
J. C HE M. E DUC.
SCIENCE & TECHNOLOGY CONCENTRATES
SCIENCE & TECHNOLOGY CONCENTRATES R NR
porous materials such as POPs and zeolites, increased the catalytic activity of the material by nearly an order of magnitude. The researchers successfully tested the material by oxidizing an organic phosphate nerve agent simulant, but they assume PPOPs will be effective against other toxic industrial chemicals, especially as part of an air filter in protective masks.—SR
could have come from natural sources or drilling fluids, but the researchers lack predrilling data for those substances for comparison.—PK
INCAS DOPED THEIR SACRIFICE VICTIMS
CH3 N+ N+
2 CF3SO3–
F
CF3
In 1999, archaeologists discovered the mummies of three Inca human sacrifice WATER CONTAMINATION victims near the 22,000-foot summit of Llullaillaco volcano in the Andes MounRISES IN TEXAS AFTER tains. The 500-year-old remains were so reNATURAL GAS DRILLING markably preserved in the cold, arid climate Determining whether shale gas production that medical researchers have been able to leads to tainted groundwater is tough, in detect molecular evidence of tuberculosis part because predrilling water quality meaand other diseases in the remaining body surements are usually lacking. But thanks fluids (C&EN, May 20, page 32). A team of to tests done in the 1990s by the Texas scientists led by Andrew S. Wilson of the Water Development Board, some predrillUniversity of Bradford, in England, now ing data are available for aquifers atop the reports that the 13-year-old female mummy Barnett Shale in northern Texas. Researchfound at the site was doped with cocaine and ers comparing samples from Barnett water alcohol (Proc. Natl. Acad. Sci. USA 2013, DOI: wells with those predrilling data report 10.1073/pnas.1305117110). Using mass specthat wells near natural gas production sites trometry to analyze segments of the Llullaillaco maiden’s hair nearest her scalp, the team DRINKING-WATER DATA discovered that, in the PREDRILLING POSTDRILLING year prior to her death, WELLS NEAR the girl had consumed CONCENTRATION, GAS EXTRACTION REFERENCE µg/L SITES WELLS an increasing amount of Arsenic 2.8 12.6 6.9 coca leaves and alcohol, Selenium 3.9 33.3 nd as revealed by increased Strontium 1,029 2,320 1,610 levels of cocaine and Barium 57.2 32.3 22.4 the cocaine metabolites Methanol na 33,600 27,400 benzoylecgonine and Ethanol na 4,500 6,800 cocaethylene, the latter na = not available. nd = not detected. SOURCE: Environ. Sci. Technol. of which is produced in the presence of alcohol. have elevated levels of arsenic, selenium, The researchers argue that the doping may and strontium (Environ. Sci. Technol. 2013, have facilitated consent or compliance of DOI: 10.1021/es4011724). Brian E. Fontenot the children chosen for sacrifice.—SE of the University of Texas, Arlington, and coworkers sampled 91 water wells in the NEW TWIST ON CHIRAL current drilling area and analyzed them with mass spectrometry and gas chromaFLUORINATION tography methods. The average arsenic, selenium, and strontium concentrations Recent advances in organofluorine chemin wells within 5 km of gas production sites istry have made fluorinated compounds— significantly exceed predrilling values widely sought as pharmaceuticals and agfrom the area, with some wells exceeding rochemicals—more readily available than U.S. drinking-water standards for the toxic ever before. One of the final frontiers is substances. Barium concentrations, meandeveloping general methods for selectively while, fell. It’s unclear whether gas producmaking compounds with chiral C–F bonds. tion activities caused these trends, the A European research team has now develresearchers say, but the trends were less oped a chiral version of a popular fluorinatremarkable or absent in reference water ing reagent that could help streamline such wells far from gas production sites. Some efforts (Angew. Chem. Int. Ed. 2013, DOI: wells also had methanol and ethanol, which 10.1002/anie.201304845). Véronique E. CEN.ACS.ORG
31
AUGUST 5, 20 13
R R
CF3
Chiral Selectfluor
NaHCO3 1,4-dioxane, room temperature
R H NR
R = various groups
R R
F
Gouverneur of Oxford University, Graham Sandford of Durham University, Peter R. Moore of AstraZeneca, and their coworkers were developing a tandem fluorinationcyclization process to make fluorinated tetracyclic compounds containing a quaternary C–F stereocenter. Such compounds could be used as intermediates for making fluorinated steroids, for example. Along the way, the researchers found that an efficient way to enantioselectively make the tetracyclic compounds was by using a chiral derivative of Selectfluor. They prepared the reagent by adding phenyl groups to Selectfluor’s framework.—SR
SMALL GOLD CLUSTERS MEAN BIG ACTIVITY Once thought inert, gold has been recognized during the past decade as a powerful catalyst for oxidations and other reactions. Calculations and experiments have indicated that the catalytic activity of nanosized gold clusters containing only a few atoms of the precious metal should be extremely high. But scientists haven’t had an optimal way to prepare and study them, until now. Avelino Corma of the Institute of Chemical Technology at Polytechnic University of Valencia, in Spain, and colleagues have developed a simple way to attach gold atoms or clusters of atoms to carbon nanotubes. Using the O2 oxidation of thiophenol as an example, they showed that a single gold atom has no catalytic activity, but clusters with five to 10 atoms are highly catalytic (Nat. Chem. 2013, DOI: 10.1038/ nchem.1721). When the clusters reach a diameter greater than 1 nm, which is about 13 atoms, the catalytic activity drops to zero. The findings suggest that only the tiny clusters can adsorb and activate thiophenol and O2 simultaneously.—EKW
