SCIENCE & TECHNOLOGY CONCENTRATES
NITROPRUSSIDE COLOR MYSTERY RESOLVED A 170-year-old chemical color mystery has been solved with 17O NMR spectroscopy and other analytical techniques. The Gmelin reaction, first observed in the 1840s by German chemist Leopold Gmelin, is considered one of the most intense colorforming reactions. When nitroprusside ([Fe(CN)5NO]2–) and sulfide combine they produce a brilliant red-violet intermediate that converts rapidly to a deep-blue intermediate. The red-violet intermediate has been proposed to be [Fe(CN)5(HSNO)]3– or [Fe(CN)5(SNO)]4–, but its structure was never confirmed. The identity of the blue intermediate has remained unknown, as has that of its decomposition products. Gang Wu and coworkers at Queen’s University, in Ontario, have now used 17O, 15N, and 13C NMR along with UV-visible and infrared spectroscopy and quantum chemical computations to show that the red-violet intermediate is [Fe(CN)5N(O)S]4– and the blue molecule is [Fe(CN)5N(O)SS)]4– (Chem. Eur. J. 2015, DOI: 10.1002/chem.201503353). Nitroprusside is used to treat hypertension, and the new findings could aid understanding of its mode of action, Wu says.—SB
STRESSED PLANTS NIX BAD CHLOROPLASTS In stressful conditions such as drought and high temperature, a plant cell’s chloroplasts can become damaged and produce harmful reactive oxygen species (ROS). Researchers
SALK INSTITUTE
This TEM image reveals a damaged chloroplast (white arrow) with its contents leaking out.
at the Salk Institute have uncovered that plants produce an enzyme to signal cells to degrade ROS-produc5 µm ing chloroplasts before they do too much damage (Science 2015, DOI: 10.1126/science. aac7444). The team led by Jesse D. Woodson and Joanne Chory first created a strain of Arabidopsis thaliana sensitive to photooxidative stress. With transmission electron microscopy the researchers observed cells degrading damaged chloroplasts, which leak out their contents. With these green organ-
AN ALKENE CARBOAMINATION Looking to turn simple alkenes into more complex molecules, chemists at Colorado State University report a stereospecific carboamination of C=C bonds. The reaction provides a new way to synthesize functionalized amines, which are often O components of biologiO N cally important molecules. CO2CH3 O The rhodium-catalyzed Rh catalyst, CO2CH3 O reaction (example shown), methanol Enoxyphthalimide developed by Tomislav Rovis N O O + and Tiffany Piou, adds a C–C bond and a C–N bond across H3CO2C CO2CH3 an alkene’s double bond Alkene (Nature 2015, DOI: 10.1038/ nature15691). Enoxyphthalimides serve as both the carbon and the nitrogen source in the intermolecular transformation. The reaction takes place in a syn fashion with both new bonds forming on the same side of the alkene. Developing a bulky cyclopentadienyl ligand for rhodium and using methanol as a solvent proved critical to getting the reaction to work. The team now has its sights set on an asymmetric version of the reaction.—BH
elles destroyed, young plants never became green. The researchers then bred a second mutant plant that also underwent photooxidative stress but did turn green, indicating that chloroplasts were damaged but not destroyed. A genetic screen of these plants revealed a mutation disabling an enzyme called plant U-box 4 E3 ubiquitin ligase, suggesting that chloroplast degradation depends on that enzyme acting as a stress signal. Understanding this mechanism may help scientists create better drought- or temperature-resistant plants.—JL
IONIZATION CHARGE DYNAMICS TRACKED In a step toward steering electrons inside molecules to control chemical reactivity, researchers report following electron-hole migration in iodoacetylene (H–C≡C–I) with 100-attosecond resolution after ionizing the molecule with a laser (Science 2015, DOI: 10.1126/science.aab2160). How the electron hole migrates depends on the orientation of the molecule relative to the direction the laser light is polarized. Led by ETH Zurich’s Hans Jakob Wörner, the researchers used a technique called high harmonic generation in which a laser pulse causes an electron to tunnel out and away from an atom—in this case, primarily the iodine of iodoacetylene. When the electron and hole recombine, the process releases a burst of attosecondCEN.ACS.ORG
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duration X-rays. If the molecule is perpendicular to the laser polarization field when it is ionized, the hole initially localizes on the iodine. The hole then delocalizes over the molecule before localizing on the carbons. If the molecule is parallel to the laser polarization field, the hole localizes mostly on the carbons.—JK
PRECISE DNA ORIGAMI Nanotechnology researchers face an unending chorus of questions about how they will scale their work up. But Jonas J. Funke and Hendrik Dietz at the Technical University of Munich have been more curious if they could shrink the scales instead. The duo has developed DNA origami scaffolds that can control the position of molecules down to a precision of 0.04 nm (Nat. Nanotechnol. 2015, DOI: 10.1038/nnano.2015.240). These scaffolds set a spatial resolution record and could be used as rulers to probe chemical interactions or to help build synthetic enzymes, Dietz tells C&EN. Each DNA scaffold is a triangle with two rigid, intersecting legs that anchor different compounds. The third leg is an “adjuster helix” that allows the researchers to control the angle between the two rigid sides. By using different adjuster helices, the German team can finely tune the distance between the compounds on the rigid legs from 1.5 to 9 nm with more than 120 discrete spacing steps in between.—MD
