Science Concentrates SOLAR POWER ANALYTICAL CHEMISTRY
CREDIT: SCI. ADV. (SPIRO-OMETAD); SHUTTERSTOCK (HONEY)
▸ Identifying honey’s floral origins Honey is big business, and often a dodgy one: It’s one of the foods most often affected by fraud. Honeys derived from a single type of flower command a higher price than polyfloral ones, creating an incentive for unscrupulous producers to dilute the golden syrup with cheap knockoffs. New research shows that NMR spectroscopy can distinguish chemical signatures of different flowers in honey, which could help snag honey cheaters (J. Agric. Food Chem. 2016, DOI: 10.1021/acs. jafc.6b00619). Honey’s floral origins are typically determined by studying pollen grains in honey samples under a microscope—a labor-intensive process. Elisabetta Schievano of the University of Padova and colleagues instead used chloroform to extract compounds from almost 1,000 samples representing 16 Italian monofloral honeys. NMR examination of the extracts revealed a spectral fingerprint for Honey fraud is each type of flower. sticky business. The researchers used more than 700 of these spectra to create a model that classified test samples according to their floral origin. Testing the model with the remaining spectra showed that they could determine not just the main floral component of each sample but secondary ones as well. The method provided 90% agreement with a pollen analysis.—ALLA KATSNELSON, special to
Holey conduction with single crystals Emerging solar-cell technologies got a boost last year thanks in part to Osman M. Bakr and his team at King Abdullah University of Science & Technology when the researchers developed single crystals of light-harvesting materials. The researchers are now double-dipping in their single-crystal strategy to try and further improve photovoltaics by turning their attention to a different component of the solar-cell anatomy: hole-transport materials. These materials conduct electrically positive charge carriers, known as holes, in both perovskite and dye-sensitized solar cells (see Note: Hydrogen not shown. page 30). The most popular hole-transSingle crystals of spiro-OMeTAD could enhance port materials are charge-carrier mobility in solar cells. amorphous thin films prepared from a polyaromatic molecule called spiro-OMeTAD, Bakr says. His team created single crystals of spiro-OMeTAD by dissolving it in dimethyl sulfoxide and then slowly exposing the solution to vapors of an antisolvent, methanol, to coax crystallization (Sci. Adv. 2016, DOI: 10.1126/sciadv.1501491). This approach allowed the researchers to report the crystal structure of spiro-OMeTAD for the first time, they say. The team further showed that the molecular packaging within a crystal allows the material to conduct holes far better than amorphous thin films currently in use.—MATT DAVENPORT
isolable version of the next heaviest group 15 analog, 2-arsaethynolate, As≤C–O–. Like its nitrogen and phosphorus analogs, 2-arsaethynolate could be a useful reagent
C&EN
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INORGANIC CHEMISTRY
▸ Arsenic joins the cyanate family Oxford University chemists who have been exploring the similarities between cyanate, N≤C–O–, and 2-phosphaethynolate, P≤C–O–, have now made the first
Ketene + –As C O 2-Arsaethynolate
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in organic synthesis or as a precursor for making electronic materials. Alexander Hinz and Jose M. Goicoechea prepared the arsenic anion by first reacting elemental
sodium and arsenic with catalytic amounts of naphthalene to make Na3As, which they protonated with tert-butyl alcohol to make NaAsH2. The researchers then treated NaAsH2 with diethylcarbonate to form As≤C–O–, isolating it as a crown ether salt (Angew. Chem. Int. Ed. 2016, DOI: 10.1002/ anie.201602310). The Oxford team found that the arsenic anion readily undergoes [2+2] cycloadditions with ketenes (shown) and carbodiimides to form four-membered arsenic-containing heterocyclic anions. With isocyanates, As≤C–O– forms five-membered heterocycles. The researchers also discovered that As≤C–O– is susceptible to decarbonylation to form arsenic clusters, including never-before-seen As102– and As124–.—STEVE RITTER MAY 2, 2016 | CEN.ACS.ORG | C&EN
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SYNTHESIS
CHEMICAL BONDING
▸ Metathesis method makes E-alkenyl halides
Delocalized form of water identified
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Cinnarizine derivative ple E-dihaloalkene, uses kinetic control to guide formation of the thermodynamically less-stable E-isomer. Hoveyda’s team used the reaction to prepare derivatives of medicinally important compounds, such as the motion-sickness drug cinnarizine (shown). Alois Fürstner, a metathesis expert at the Max Planck Institute for Coal Research, who was not involved in the research, comments that the work marks a breakthrough even though the scope of the method is currently limited to specific alkenyl halides as the products. “The results show that there is light at the end of the tunnel, which in turn will inspire future catalyst design,” Fürstner says.—BETHANY HALFORD
BIOLOGICAL CHEMISTRY
▸ Chemical cocktail induces fibroblasts to become heart cells Researchers have found that giving fibroblasts a bath in a mixture of nine chemicals can convert the collagen-producing skin cells into cardiac-like cells. A long-held
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C&EN | CEN.ACS.ORG | MAY 2, 2016
A multidisciplinary research team has found that a solitary, confined water molecule can exist in a previously unidentified state in which protons and electrons form a delocalized ring around the oxygen atom (Phys. Rev. Lett. 2016, DOI: 10.1103/physrevlett.116.167802). Alexander I. Kolesnikov of Oak Ridge National Laboratory and coworkers used neutron scattering to study water molecules trapped in cavities of the mineral beryl. These crystal lattice cavities are just large enough to fit one water molecule, with no hydrogen
A water molecule trapped in a beryl crystal cavity takes on multiple simultaneous orientations—it appears to have a central oxygen atom surrounded by an array of hydrogen atoms. bonds to other water molecules or to the beryl cavity atoms. In a classical view, the water molecule sits with the oxygen atom roughly in the center of the cavity and its two hydrogens pointing toward one of the faces, held in place by an energy barrier to rotation. Taking a quantum mechanical view, the researchers found that the water molecule can “tunnel” through the barrier and exist in multiple orientations simultaneously. The resulting structure has the centrally located oxygen surrounded by concentric rings of delocalized electrons and protons. The symmetry of this form means that the water molecule has zero electric dipole moment. The team suggests this newfound state of water could also occur in other confined spaces, such as cell membranes.—JYLLIAN KEMSLEY
group selected 83 comgoal, this type of cellular pounds, which included manipulation could give enzyme inhibitors and surgeons a source of tisepigenetic modulators sue to help repair damage after a heart attack. known to help reproA team led by Sheng gram cell growth and Ding of the University development, to steer of California, San Franthe cells toward cardiac cisco, developed the function. The researchmethod and has shown ers exposed human that the new cardiomyoforeskin fibroblasts to cytes, which are muscle various combinations cells that help the heart This immunofluorescence of the compounds, beat, can repair cardiac image shows chemical markers finding that one set of damage in mice (Science identifying a fibroblast that has nine compounds accom2016, DOI: 10.1126/ been converted to a cardiac-like plished the conversion science.aaf1502). Recell. The inset shows areas at to cardiac-like cells with searchers have been higher magnification. beating behavior. They attempting to accomthen transplanted the plish this fibroblast-to-cardiomyocyte cells into mice with cardiac damage similar conversion by a variety of methods, most to that caused by heart attacks. Two weeks notably through genetic manipulation. later, the rodent’s heart function had imHowever, the yields have been poor. Ding’s proved.—ELIZABETH WILSON
CREDIT: SCIENCE (MICROGRAPH); P HYS . REV. L E T T. ( BERY L )
When it comes to making 1,2-disubstituted olefins with metathesis chemistry, most synthetic chemists have taken sides. That is to say, they’ve tended to produce Z-olefins, in which the substituents are oriented to the same side of the double bond. Chemists led by Boston College’s Amir H. Hoveyda have now switched sides by developing a cross-metathesis route to E-alkenyl chlorides and fluorides. Selective synthesis of the E-isomers, in which the substituents are oriented to opposite sides of the double bond, had previously proven challenging via metathesis (Science 2016, DOI: 10.1126/ science.aaf4622). The new transformation, which uses a molybdenum catalyst to swap the C=C bonds between an olefin and a sim-
