Carbohydrate recognition domain
* Label Glycans
2-D MATERIALS
How to make ultrathin materials with liquid metals
Bovine serum albumin Glass slide
Representative glycans from several families (shown here in red and green) found on the TB bacterium’s surface are immobilized on an array via links to bovine serum albumin and screened against fluorescently labeled lectin fragments. the resulting array with a panel of fluorescently labeled carbohydrate-recognition fragments from one cow lectin and several human lectins (ACS Chem. Biol. 2017, DOI: 10.1021/acschembio.7b00797). Among other results, screening revealed binding of the mannose receptor and the protein DC-SIGN to two families of TB glycans, interactions that promote entry of the mycobacteria into immune-system macrophages.—STU BORMAN
C R E D I T: A DA PT ED FRO M ACS C H E M . B I O L . (G L AS S SL I DE )
INORGANIC CHEMISTRY
▸ First triazenyl radicals stabilized and characterized
Over the past decade, researchers have succeeded in making radical compounds of main group elements by stabilizing them with N-heterocyclic carbenes. Nitrogen-containing triazenyl radicals are attractive for their potential reactivity and physical properties. Free triazenyl radicals have previously been detected by electron paramagnetic resonance (EPR) spectroscopy and as ligands in transition-metal complexes, but they’ve been challenging to stabilize and isolate. ReR R searchers led by Eunsung Lee of the Institute N N N for Basic Science and N N Pohang University of N N Science & Technology R R have now synthesized Triazenyl radical and characterized a pair of triazenyl radicals stabilized by N-heterocyclic carbenes (J. R= or Am. Chem. Soc. 2017,
Just as slugs leave behind trails of goo, liquid metals can leave behind atomically thin films. Researchers at the Royal Melbourne Institute of Technology have introduced a new method that uses oozy liquid metals to create solid two-dimensional metal oxides (Science 2017, DOI: 10.1126/ science.aao4249). This approach could create 2-D films from a variety of metals, potentially broadening the range of ultrathin materials with attractive optical and electronic properties, the researchers say. Jonathan N. Coleman, a 2-D materials guru at Trinity College Dublin who was not involved in the project, calls the work “a real breakthrough.” Watch our video describing the technique at cenm.ag/liquidmetals.
DOI: 10.1021/jacs.7b08753). The researchers reacted chloroimidazolium chlorides with azides to form triazenyl cations, which they then reduced to the corresponding triazenyl radicals via one-electron reduction with potassium metal in toluene. The researchers characterized the radicals by single-crystal X-ray diffraction, EPR spectroscopy, and UV-vis absorption spectroscopy. Density functional theory calculations suggest that the unpaired electron in both radicals is strongly delocalized over the entire conjugated π system, which may be how the N-heterocyclic carbenes stabilize the triazenyl radical. The researchers demonstrated a potential application by using one of the triazenyl radicals as a cathode material in a lithium-ion battery.—CELIA ARNAUD
MOLECULAR ELECTRONICS
▸ Antiaromaticity flips single-molecule switch Ultrasmall electronic devices require ultrasmall components. That’s why scientists have been working for the past few decades on electronic circuitry in which function is controlled by just a single molecule. Those molecules nearly always sport conjugated aromatic backbones because aromaticity in those molecules usually goes hand-in-hand with enhanced conductivity. But a team led by Latha Venkataraman and Luis M. Campos of Columbia University and Jeffrey B. Neaton of Lawrence Berkeley National Laboratory has shown that aromatic isn’t the
Pinned between gold electrodes (yellow), TBTP serves as a single-molecule switch as its core undergoes reversible oxidation between a nonconducting neutral state (red) and a conducting antiaromatic dication (green). S
S
TBTP
S
S –2 e– +2 e–
only way to go: The team has demonstrated a highly Off conducting, reversible, single-molecule switch based on antiaromaticity (Sci. Adv. 2017, DOI: 10.1126/sciadv. aao2615). In classical organic chemistry, Hückel’s rule states that conjugated cyclic molecules with 4n+2 π electrons exhibit enhanced stability because they are aromatic. Related molecules with 4n π electrons are comparatively unstable and described as antiaromatic, a concept pioneered by Columbia’s Ronald Breslow, who died Oct. 25. Intrigued by the possibility that a so-called unstable antiaromatic molecule might function as a switch, the team used a scanning tunneling microscope to pin a nonconducting thiophenylidene derivative (TBTP, shown) between gold electrodes. They showed that a quick electrooxidation step reversibly removes two electrons, converting the neutral molecule to a highly conducting antiaromatic dication that works stably and reproducibly as a switch.—MITCH JACOBY NOVEMBER 6, 2017 | CEN.ACS.ORG | C&EN
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