An AFM image of 8-hydroxyquinoline on a copper surface (left) reveals hydrogenbonding interactions at low temperature. Meanwhile, an AFM image (right) of a bis(p-pyridyl)acetylene tetramer shows what appears to be unexpected electron density (arrow) between pyridyl nitrogens.
Hydrogen Bonds: Real Or Surreal?
The sighting of hydrogen bond interactions in atomic force microscopy (AFM) images, highlighted in C&EN last year, may be an experimental artifact. The images published by a group of researchers in China appear to show electron density where hydrogen bonds would connect 8-hydroxyquinoline
molecules (Science 2013, DOI: 10.1126/ science.1242603). But what the group imaged may have been caused by the interaction of the AFM tip with the potential energy surface between the molecules, according to work published this year by a separate team led by Sampsa Hämäläinen and Peter Liljeroth of Aalto University School of Science, in Finland, and Ingmar Swart of Utrecht University, in the Netherlands (Phys. Rev. Lett. 2014, DOI: 10.1103/ physrevlett.113.186102). “We’re not saying there can be no contribution from hydrogen bonds,” Swart said, “but we show that
MATERIALS SCIENCE
More Graphene Surprises
Mater. 2014, DOI: 10.1021/cm5026552). The team found that surfaces of the photocatalytic nanoparticles generate hydroxyl radicals, which oxidatively attack RGO. The process causes RGO sheets to fragment, forming polyaromatic hydrocarbon compounds. The group reported that continued exposure to UV light eventually decomposes the organic compounds completely, leaving behind CO2 and water. And graphene surprised researchers in another way this year. Andre K. Geim of the University of Manchester, in England, and coworkers demonstrated that pristine single layers of graphene—thought to be impermeable—can conduct protons unexpectedly well (Nature 2014, DOI: 10.1038/nature14015). This finding could make the material attractive for use in fuel cells, which require a thin proton-conducting membrane.—MITCH JACOBY
Researchers are shocked to find that the thin carbon sheet can decompose and can conduct protons
Ultrathin films of carbon known as graphene have generated intense interest because of the potential applications enabled by the material’s outstanding physical and chemical properties. One of those properties, chemical stability, was called into question this year by an investigation showing that the material can decompose when used as a supporting layer in catalysis and in electronic devices. For those applications, researchers typically conduct studies using a solution-phase form OH• of graphene called reduced graphene oxide, or RGO. But RGO may not be as stable as assumed. Prashant V. Kamat of the University of Notre Dame and colleagues demonstrated that aqueUV light initiates an oxidation ous suspensions of process that decomposes a waterdispersible form of graphene, RGO-supported TiO2 as depicted in this cartoon that nanoparticles unexillustrates fragmentation (not pectedly decompose actual bonding) and indicated upon exposure to ulby the gradual lightening of the solutions. traviolet light (Chem. CEN.ACS.ORG
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DECEMBER 22, 2014
OH•
CO2 + H2O
JAMES G. RADICH/AU BURN U
Downloaded by UNIV OF MICHIGAN ANN ARBOR on September 15, 2015 | http://pubs.acs.org Publication Date (Web): March 31, 2015 | doi: 10.1021/cen-09251-cover3
Bonds imaged by AFM last year may be an artifact of the technique, leaving the discovery in question
you can also have contrast when there is no bond at all.” Swart and his colleagues used AFM to study tetramers of bis(p-pyridyl) acetylene molecules. The tetramers are held together by intermolecular C–H···N hydrogen bonds and bring two nitrogen atoms on separate molecules within 3 Å of each other. The nitrogens should have no bonding interaction, yet AFM images appear to show a bond between the atoms. The results emphasize that researchers must be cautious about interpreting highly processed microscopy images, said James K. Gimzewski of the University of California, Los Angeles, and California NanoSystems Institute. “The nano is invisible, and images of it should be treated with care.”—JYLLIAN KEMSLEY
SCIENCE (LEFT)/ PHYS. REV. LETT. (RIGHT)
MICROSCOPY
