CREDIT: ACS APPL. MATER. INTERFACES (SPHERES); ANGEW. CHEM. INT. ED. (BALL & STICK MODEL)
shallow-water food webs rely primarily on photosynthesis. In fact, chemosynthesis— getting energy from redox reactions instead of light—may play key ecosystem roles well beyond deep-sea communities (Curr. Biol. 2016, DOI: 10.1016/j.cub.2016.10.034). “For a long time, chemosynthesis in shallow waters was seen as an interesting oddity,” says the University of Plymouth’s Nicholas D. Higgs, whose team made the discovery. “We’ve shown it supports a multi-million-dollar lobster industry.” While snorkeling after his wedding in the Bahamas, Higgs noticed broken remnants of clam shells from a species called Codakia orbicularis, which has relatives that live around deep-sea vents, an ecosystem he studies. Knowing that C. orbicularis relies on symbiotic bacteria that generate energy by oxidizing sulfur, Higgs wondered who was eating the clams. His team fingered the spiny lobster using isotope analysis. By measuring sulfur, nitrogen, and carbon isotope ratios in both the clam and the lobster, they discovered that the clams make up 20% of the lobster’s diet.—SARAH EVERTS
NANOMATERIALS
▸ Hairy particles make versatile coatings Nanoparticle-based coatings help researchers tailor the optical and mechanical surface properties of the objects they cover. Creating coatings with different surface properties, however, typically demands that researchers make different suspensions filled with different nanoparticles tailored for each new application. Joseph L. Keddie of the University of Surrey and his colleagues have now developed “hairy” particles that could simplify that process. They created spherical copolymer particles adorned with mops of poly(methacrylic acid) chains. At low pH, the chains are protonated and remain collapsed against a particle’s core. As the pH rises, the chains deprotonate and extend. By mixing these size-shifting particles with larger, fixed-size acrylate
Nanoparticles with growing polymer “hairs” nearly double in diameter—from about 50 nm to more than 90 nm—between pH 3 and pH 10.
SYNTHESIS
Radical route to resveratrol oligomers Resveratrol—made famous by its presence in red wine—has been touted for its health benefits. Oligomers of the compound may have even more promising medicinal properties, as they exhibit anti-inflammatory, immunomodulatory, and cytotoxic activities in cell studies. But O getting enough of these complex poly(CH3)3Si Si(CH3)3 phenols to study their mechanisms of action has been challenging. Chemists RO led by the University of Michigan’s Corey Stephenson and the University of Ottawa’s Derek OR • Pratt now report a stereoconvergent synthesis H of the resveratrol tetramers nepalensinol B and vateriaphenol C in 13 steps (Science 2016, DOI: 10.1126/science.aaj1597). Their stratO H OR RO egy makes use of a persistent radical R = benzyl (shown) that’s derived from the resverPersistent radical atrol dimer, ε-viniferin. “Persistent free radicals have become indispensable in the synthesis of organic materials through living radical polymerization,” the chemists point out in the report. “However, examples of their use in the synthesis of small molecules are rare.” Stephenson and Pratt note that thermodynamic stereocontrol in the dimerization of persistent free radicals plays a critical role in their strategy.—BETHANY HALFORD
particles, the team created a variety of coating motifs (ACS Appl. Mater. Interfaces 2016, DOI: 10.1021/acsami.6b12015). For instance, at acidic pH, these two-particle suspensions dry to form layered coatings with smaller, hairy particles sitting atop the larger ones. But at basic pH values, the colloids dry into homogenous coatings. This variety of coating styles should allow researchers to use a single colloidal suspension to tune surface properties such as hardness, reflectivity, and potentially even stickiness, the Surrey team says.—MATT DAVENPORT
CHEMICAL BONDING
▸ Six bonds to carbon: Confirmed Among chemistry’s most fundamental concepts is that carbon is tetravalent and forms four bonds to other atoms. And when it comes to aromaticity, benzene’s hexagonal planar ring structure is taken as gospel. Chemists have thus been fascinated by finding exceptions to these truths. One example is hexamethylbenzene dication, C6(CH3)62+, a molecule first prepared in 1973 and suspected of not only having a six-coordinate carbon atom but also of being nonplanar.
Pyramidal C6(CH3)62+ contains the first confirmed example of six-coordinate carbon; carbon = gray, hydrogen = white. But the structure has only l been inferred by spectroscopy. Moritz Malischewski and Konrad Seppelt of Free University of Berlin have now reported the first X-ray crystal structure for C6(CH3)62+, confirming it has a pentagonal pyramidal C6 framework with a six-coordinate carbon at the apex of the molecule (Angew. Chem. Int. Ed. 2016, DOI: 10.1002/anie.201608795). Like other nonclassical carbocations, such as CH5+ and the norbornyl cation (C7H11+), experimental proof of the C6(CH3)62+ structure proved challenging. The team first prepared an epoxide of hexamethyl Dewar benzene (a bicyclic benzene isomer) and then dissolved the epoxide in magic acid (HSO3F/SbF5) and added anhydrous HF at low temperature. Under these superacidic conditions, O2- is pulled off to generate C6(CH3)6(SbF6)2•HSO3F. Structural and computational analysis revealed that the molecule retains its aromaticity.—STEVE
RITTER DECEMBER 12/19, 2016 | CEN.ACS.ORG | C&EN
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