PERSISTENT POLLUTANTS
▸ POPs persist in the deep blue sea An alphabet soup of persistent organic pollutants—including polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and polycyclic aromatic hydrocarbons (PAHs)—is carried by the wind and rivers into the ocean. A new study bolsters findings from scant prior sampling showing that these compounds riding on ocean currents have penetrated as far as 2,500 meters deep in the Atlantic Ocean (Environ. Sci. Technol. 2016, DOI: 10.1021/acs.est.5b05891). Rainer Lohmann
REAGENTS
Stable phosphorus carbene analog debuts
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Carbenes were once thought to be transient species featuring a neutral carbon with a pair of unshared electrons that formed during chemical reactions. Given the instability, the best chemists could do was invoke them by proposed reaction mechanisms. With time, researchers designed molecular frameworks to house carbenes so that they were persistent enough to be isolated, namely N-heterocyclic carbenes and cyclic alkyl-amino carbenes. These molecules now serve as ligands to bind and stabilize metals and as organocatalysts. Phosphinidenes, the Ar phosphorus anaN •• •• logs of carbenes, P P are now following Ar = N a similar course of development. Ar After years of A (phosphino)phosphinidene, working with a stable carbene analog transient phosphinidenes, a team led by Guy Bertrand of the UCSD-CNRS Joint Research Chemistry Laboratory at the University of California, San Diego, has prepared the first phosphinidene that’s stable for weeks at room temperature (Chem 2016, DOI: 10.1016/j.chempr.2016.04.001). As with carbenes, the secret to making a stable phosphinidene has been finding just the right combination of substituents––a π-donating phosphorus substituent and superbulky aryl groups. Without the steric protection, the phosphinidene dimerizes and extinguishes itself. In preliminary reactions, the team found that the electron lone pair enables the phosphinidene to undergo addition reactions with alkenes and isonitriles.—STEVE RITTER
CREDIT: SHUTTERSTOCK (WINE); THOMAS SOLTWEDEL (OCEANOGRAPHERS)
Oceanographers prepare to lower a polyethylene sampler (enclosed in a metal cage) into the North Atlantic. With the samplers, the scientists have confirmed the presence of persistent organic pollutants in the deep ocean. of the University of Rhode Island and colleagues deployed samplers at various depths at mooring sites in the North Atlantic and in the tropical Atlantic to measure organic pollutants dissolved in the water. The samplers contained polyethylene films that sorb dissolved organic contaminants. After a year, the researchers collected the films, extracted the compounds, and analyzed them using gas chromatography-mass spectrometry, searching for 78 target pollutants that included PCBs, PBDEs, and PAHs. The deep ocean is “clearly not highly polluted” with these compounds, Lohmann says, but they are surprisingly prevalent “for what we thought of as being a fairly pristine body of water.”—DEIRDRE LOCKWOOD,
special to C&EN
FOOD
▸ Sensing technique identifies white wine
Fluorescence quenching of PPE 1 and PPE 2 (shown) can help distinguish several white wine varietals, including Riesling, Chardonnay, and Sauvignon Blanc. R´
When you buy a bottle of white wine, how do you know that the liquid inside corresponds to the Riesling, Chardonnay, or Sauvignon Blanc varietal written on the label? Variations in weather, geography, and pruning can impact a given year’s complex chemical makeup, even PPE 1 among wines PPE 2 from the same grape variety, making it difficult to develop analytical techniques for wine fingerprinting. Researchers led by Uwe H. F. Bunz of Heidelberg University have reported a new telltale sensing technique based on fluorescence quenching of wine alcohols, sugars, and natural colorants by two oppositely charged poly(p-phenyleneethynylene)s called PPE 1 and PPE 2 (Angew. Chem. Int. Ed. 2016, DOI: 10.1002/
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R´= –CH2COO– R´= –(CH2)3N(CH3)3+
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anie.201602385). Using an array of anionic PPE 1 and cationic PPE 2 at different pH levels, the team found that it could distinguish an assortment of white wines according to their type of grape. Although researchers have been developing wine-sensing methods based on mass spectrometry, colorimetric assays, and other techniques, “we don’t have the magic bullet yet,” comments Susan E. Ebeler, a wine chemist at the University of California, Davis. The new work is a promising first step, she adds.—SARAH EVERTS JUNE 27, 2016 | CEN.ACS.ORG | C&EN
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