Science Concentrates INORGANIC CHEMISTRY
▸ All-nitrogen ring crystallized
SPECTROSCOPY
▸ STM measures vibrations between two molecules Forces between closely spaced molecules can cause them to undergo various types of concerted motions or intermolecular vibrations. This kind of molecular group dance can alter vibrations within individual molecules and influence chemical reactivity. Yet details of these collective molecular motions remain unknown because the coupled vibrations of a single pair of molecules have not been measured—until now, that is. Zhumin Han and Wilson Ho of the University of California, Irvine, and coworkers used a specially designed scanning tunneling microscope to probe the coupled vibra-
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C&EN | CEN.ACS.ORG | JANUARY 30, 2017
Using nanoparticulate red phosphorus (photo of 0.5 g of powder and micrograph) to make battery anodes boosts charge storage capacity.
ENERGY STORAGE
Phosphorus boosts lithiumion battery charge capacity Using a solution-phase process to prepare red phosphorus in nanoparticle form, researchers in Taiwan have converted the inexpensive phosphorus allotrope from an electrochemically weak material to a highly promising one (Nano Lett. 2017, DOI: 10.1021/acs.nanolett.6b05081). The team, led by Hsing-Yu Tuan of National Tsing Hua University, demonstrated that the nanomaterial can be used to make lithium-ion-battery anodes with higher charge storage capacity than the graphite ones used commercially. Battery researchers have tried previously to take advantage of red phosphorus’s large theoretical charge capacity, which is roughly seven times as high as graphite’s. But phosphorus is a poor electrical conductor and swells drastically during lithiation cycles, causing anodes to crack. Blending phosphorus with carbon, which is a common approach, improves conductivity but dilutes the phosphorus, limiting the boost in charge capacity. So Tuan’s group formed iodine-doped red phosphorus nanoparticles by reacting PI3 with ethylene glycol and cetyltrimethylammonium bromide. Pellets formed from the nanoparticles exhibit conductivities more than 10 billion times as high as that of commercial red phosphorus. Anodes made from the new material show an initial charge capacity that reaches red phosphorus’s theoretical value and falls slowly over hundreds of charge cycles.—MITCH JACOBY
tions of two CO molecules—one on the STM tip and one on a silver surface (Phys. Rev. Lett. 2017, DOI: 10.1103/physrevlett.118.036801). The vibrations are induced by
The close proximity of two CO molecules (black and red)—one on an STM tip and one on a surface—induces vibrations. In the mode shown here, the molecules move in opposite directions, with the oxygens moving more than the carbon atoms (arrows).
CREDIT: NANO LETT. (MICROGRAPH, POWDER); WILSON HO & ZHUMIN HAN/UC IRVINE (STM)
Molecules packed with nitrogen are known for their explosive properties, which are prized for applications such as weapons and propellants. One long-desired synthesis target, an all-nitrogen aromatic ring, was prepared as the cyclopentazolate anion in tetrahydrofuran solution last year (C&EN, July 18, 2016, page 8). Now, researchers have N N managed to isolate N N N and characterize Cyclopentazolate it in the solid state (Science 2017, DOI: anion 10.1126/science. aah3840). After “hundreds of experiments,” a team led by Bingcheng Hu of Nanjing University of Science & Technology prepared the compound through oxidative dearylation to cleave the C–N bond in 3,5-dimethyl-4-hydroxyphenylpentazole, yielding cyclo-N5– in the form of (N5)6(H3O)3(NH4)4Cl. The pentazolate anion is stabilized by hydrogen bonds from the ammonium and hydronium cations. The white salt is stable in air at room temperature and doesn’t begin to decompose until 117 °C, although a crystal stored at ambient temperature in ethyl acetate slowly decomposed over six months, forming NH4N3, the researchers report.—JYLLIAN KEMSLEY
short-range CO-CO repulsion. The team tuned the distance between the two molecules while measuring inelastic electron tunneling, which is the basis of a highly sensitive vibrational spectroscopy method, and analyzed the results with quantum calculations. The analysis revealed various molecular subtleties, including an antisymmetric vibrational mode corresponding to a type of hindered translational motion. The team explains that these vibrational features, which can be used to deduce chemical information, result from the complex interplay between tip-sample distance and the tilting and orbital alignment of the pair of CO molecules.—MITCH JACOBY
ELECTRONIC MATERIALS
▸ Health trackers on the cheap
CREDIT: INTEGRATED NANOTECHNOLOGY LABORATORY/KAUST
Muhammad M. Hussain and his team at King Abdullah University of Science &
A 3-D-printed wearable device features a pulse tracker (left), temperature monitor (center), and moisture sensor (right), all made from inexpensive materials. Technology are on a path paved with sticky notes and silicon to make wearable health trackers more affordable for everyone. Using sticky notes, silver ink, aluminum foil, and clean-room wipes, Hussain’s team created low-cost pressure, moisture, and temperature sensors connected to flexible silicon circuits for data handling and transmission. The team’s work has been accepted and will be published soon in Adv. Mater. Technol. By printing silver ink coils and capacitors on cellulose sticky note substrates, the team created simple temperature and moisture sensors, respectively. Changing temperatures are
BIOBASED MATERIALS
Epoxy resins without BPA A biobased bisphenol can be used to prepare renewable epoxy-amine resins, eliminating the need to use potenially-toxic bisphenol A, chemists report (ChemSusChem 2017, DOI: 10.1002/cssc.20d1601595). BPA is a petroleum-based endocrine disruptor and has been banned by the Food & Drug Administration for use in children’s product packaging. Epoxies, with their hardy chemical and thermal properties, are ubiquitous, used in materials OH HO such as electronics and insuBisphenol A lators. Scientists have been avidly looking for substitutes CH3O for BPA in epoxies. A team led by OCH3 HO Florent Allais of AgroParisTech O has found that syringaresinol, a naturally occurring, non-enOH CH3O docrine-disrupting bisphenol O found in plants such as Syringa OCH3 patula and Magnolia thailandSyringaresinol ica, can be used to produce epoxy-amine resins. The researchers developed a synthesis of syringaresinol via a chemo-enzymatic pathway. Though the epoxy-amine resins based on syringaresinol have mechanical and thermal stabilities that are close to that of BPA-produced resins, the authors say, “the search for a biobased bisphenol able to compete with BPA is not over yet.”—ELIZABETH WILSON
detected as changes in the ink’s electrical resistance, whereas the paper’s dielectric permittivity responds to moisture introduced by sweat, measurably altering the sensor’s electronic profile. To track a person’s pulse, the team built pressure sensors with clean-room wipes sandwiched between strips of aluminum foil. A wipe’s microfibers compress and relax along with the staccato blood flow through the wrist’s radial artery, causing the sandwich sensor’s capacitance to fluctuate with the heartbeat. Each sensor is mounted to a 3-D-printed wristband, resulting in a device that costs about $25 to make, the team reports.—MATT DAVENPORT
MASS SPECTROMETRY
▸ Extending the capabilities of mass spectrometry Mass spectrometry can provide information about the composition of large biomolecular machines, but only if the instrument can handle high mass-to-charge ratios (m/z) with good resolution. That
becomes even harder with complexes that include both proteins and nucleic acids because the nucleic acids don’t acquire enough charge to bring the complexes within the mass range of most instruments. A team led by Albert J. R. Heck of Utrecht University has now modified an Orbitrap mass spectrometer so that it has an ultrahigh mass range, more than twice that of the commercially available Orbitrap extended mass range instrument (Nat. Methods 2017, DOI: 10.1038/nmeth.4147). The researchers achieved this improvement with modifications that increased the transmission and resolution of ions with greater than 20,000 m/z. To demonstrate the instrument’s performance, the researchers analyzed intact bacterial ribosomes and their subunits. The improvements enabled the researchers to resolve relatively small mass differences associated with heterogeneity in the subunits and with the binding of a small ribosomal-associated protein. The researchers also showed that the instrument could analyze a 9-megadalton virus. They propose that such high mass capabilities could make mass spectrometry useful as a quality-control tool for large biological complexes prior to analysis by electron microscopy or crystallography.—CELIA ARNAUD JANUARY 30, 2017 | CEN.ACS.ORG | C&EN
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