ANALYTICAL CHEMISTRY
Hybrid method sequences carbohydrates Combination of mass spec and IR spectroscopy identifies stereochemistry of bond between sugars Methods for routine sequencing of carbohydrates lag behind those for sequencing nucleic acids and proteins. The lack of such methods makes fully characterizing carbohydrates difficult. Sequencing a carbohydrate is a challenge because many of the sugar building blocks are isomers of one another, making it hard to distinguish between them, and the stereochemistry of glycosidic bonds connecting the sugars must be characterized to fully analyze the carbohydrate’s structure. Reseachers led by Isabelle Compagnon of the University of Lyon report a hybrid method that allows them to sequence carbohydrates by combining infrared laser spectroscopy with mass spectrometry (Nat. Commun. 2017, DOI: 10.1038/s41467-01701179-y). They break carbohydrates into monosaccharide fragments in the mass spectrometer with gas collisions. Those
Y HO
O HO
Z
OH
OH O
O HO
HO
NH
OH
B C O When a disaccharide dissociates at its glycosidic oxygen, IR signatures of C fragments contain stereochemical memory of the glycosidic bond. B, Y, and Z refer to the other possible fragments. fragments are then further dissociated with IR photons from a tunable light source to record the IR spectra of the fragments. The researchers first used the method to analyze disaccharides. They showed that the IR fingerprints of a particular type of monosaccharide fragment—the socalled C fragment—can be used to identify
the monosaccharide content and can contain stereochemical information about the glycosidic bond between the sugars. The team then applied the sequencing approach to longer oligosaccharides. “The key insight that this study provides is that the chirality of the glycosidic bond oxygen is not altered even when the glycosidic bond is cleaved,” says Nicolas C. Polfer of the University of Florida, who also combines mass spectrometry with IR spectroscopy. “This observation has important ramifications for carbohydrate sequencing, as the glycosidic bond is generally the most labile bond in larger saccharides.” Nicola Pohl, a chemistry professor at Indiana University, Bloomington, who also develops analytical methods for carbohydrates, wonders how well the method will translate to a wide range of monosaccharides. “Will this IR technique produce enough distinct signatures to be diagnostic for all possible sugars?” she asks.—CELIA ARNAUD
CONSUMER PRODUCTS
Triclosan lingers in toothbrushes
C R E D I T: S H U TT E RSTO CK
Bristles and tongue cleaners accumulate toothpaste compounds take up some compounds, including triNew research shows that compounds in closan, researchers led by Baoshan Xing of toothpaste, including the antimicrobial agent triclosan, can build up in toothbrush the University of Massachusetts, Amherst, set out to determine the fate of chemiheads and leach back out over time (Encals in toothpaste. They simulated three viron. Sci. Technol. 2017, DOI: 10.1021/acs. months of toothbrushing in the lab with est.7b02839). 22 types of manual toothbrushes, artificial Triclosan was once a common composaliva, and six best-selling nent of antibacterial soaps Cl OH antibacterial toothpastes and body washes in the U.S. containing 0.3% triclosan Last year, the U.S. Food O (3 mg/g of toothpaste). & Drug Administration Triclosan and other toothgave companies a deadline Cl Cl paste chemicals accumulated of Sept. 6, 2017, by which Triclosan in elastomeric toothbrush to stop marketing those head components such as cheek and products, citing concerns about triclosan tongue cleaners, as well as nylon bristles. causing antibiotic resistance and a lack of More than half the toothbrushes accumuevidence that triclosan-containing soaps lated at least 10 mg of triclosan over the were more effective than soap and water simulated three-month brushing. When alone. The compound’s use in toothpaste the researchers switched some of those is still approved, though, because of retoothbrushes to non-triclosan toothpastes ports that it reduces gum inflammation, for two weeks of simulated brushing, trigingivitis, and plaque. closan leached out of the toothbrushes. Because some nylons—materials comAlthough triclosan uptake and release monly used in toothbrush bristles—can
did not reach harmful levels—the U.S. Environmental Protection Agency’s limit for chronic dietary exposure is 0.3 mg of triclosan per kg of body weight per day— the authors point out that this represents previously unrecognized sources of exposure to both humans and the environment, including transport to landfills through discarded toothbrushes. “This study really highlights how little we know about the fate of antimicrobial chemicals,” says Erica Hartmann, a civil engineer at Northwestern University who studies antimicrobial resistance. “Every time one of these chemicals winds up in a new context, that’s another opportunity for it to have unintended consequences.”—EMMA HIOLSKI OCTOBER 30, 2017 | CEN.ACS.ORG | C&EN
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