Science Concentrates MATERIALS
▸ Nonlinear optical laser material avoids beryllium
Li2B6O9F2 offers deep-ultraviolet nonlinear optical properties without beryllium and debilitating layering. materials currently used (Angew. Chem. Int. Ed. 2017, DOI: 10.1002/ anie.201700540). DUV NLO materials are increasingly being used in the semiconductor industry and are crucial in producing solid-state lasers with wide frequency ranges. The fluorooxoborate KBe2BO3F2, which is the only practical laser material for generating light below 200 nm, has had researchers scrambling for alternatives to avoid further use of toxic beryllium. It also grows in layers, which can reduce its optical properties. Now, a team led by Shilie Pan, vice director of the Chinese Academy of Science’s Xinjiang Technical Institute of Physics & Chemistry, has prepared a class of beryllium-free fluorooxoborate crystals that don’t layer. The team’s strategy involved inserting (BO3F)4−, (BO2F2)3−, or (BOF3)2− groups into three-dimensional boron-oxygen networks. The material works as needed without beryllium, and the synthesis method avoids the formation of terminal oxygen atoms—the existence of which leads to layer formation. One compound in particular, Li2B6O9F2, promises to further “break down the DUV wall for NLO materials,” the researchers report.—ELIZABETH WILSON
BIOCATALYSIS
▸ Indole alkaloid biosynthetic pathways unraveled Indole-based alkaloid natural products such as fischerindoles and hapalindoles have
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C&EN | CEN.ACS.ORG | MARCH 13, 2017
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Sweetener tracks tinkling in the pool
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O S
N– K + O
Acesulfame potassium
Researchers estimate that swimming pools contain 30 to 80 mL of urine for each person who’s jumped in. The problem, aside from the ick factor, is that urine reacts with chemical disinfectants in the water to form potentially harmful by-products. To track the safety of pools and hot tubs, scientists would like to find a chemical marker of how much urine is actually in the water. Xing-Fang Li and coworkers at the University of Alberta propose that the artificial sweetener acesulfame potassium—used in products such as beverages and baked goods, often in combination with other sweeteners—could be that marker. Humans don’t metabolize the sweetener, so it’s excreted intact in urine. Li and coworkers used liquid chromatography and tandem mass spectrometry to measure acesulfame in 250 samples from 31 pools and hot tubs in two Canadian cities. They also sampled the corresponding input tap water for comparison (Environ. Sci. Technol. Lett. 2017, DOI: 10.1021/acs. estlett.7b00043). The team found the sweetener in all pool and hot-tub samples at concentrations from 30 to 7,110 ng/L, compared with 15 ng/L or less in the tap water samples. Using the average amount of acesulfame in a human urine sample, the researchers then estimated that urine can account for up to 30 L of the volume in a standard 420,000-L community pool. The ubiquity of acesulfame suggests that it could indeed be used as a urinary marker for tracking water quality, the researchers note.—CELIA ARNAUD
The enzymes AmbU4, WelU1, promising antimicrobial and antitumor activities, and WelU3 use cascade but they are difficult to make synthetically. New reactions to convert a common findings on how cyanobacteria biosynthesize them indolenine precursor into three could help guide future synthetic efforts. Xinyu Liu natural products. and Qin Zhu at the University of Pittsburgh have discovered that U-protein enzymes catalyze cascade reactions that H structurally diversify a common precursor into NC H WelU3 NC different indole alkaloids N (Chem. Commun. 2017, N DOI: 10.1039/c7cc00782e). Indolenine precursor H For example, three of the 12-epi-Hapalindole C AmbU4 enzymes—WelU1, WelU3, WelU1 and AmbU4—convert a single indolenine into a tetracyclic fischerindole, a CN H tricyclic hapalindole, and a H NC tetracyclic hapalindole, reH spectively. Each enzyme’s H cascade reaction includes N N a Cope rearrangement, an H H aza-Prins cyclization, and 12-epi-Hapalindole U 12-epi-Fischerindole U a carbocation-deposition
CREDIT: SHUTTERSTOCK (POOL); ANGEW. CHEM. INT. ED. (CRYSTAL STRUCTURE DIAGRAM)
Materials scientists have developed a new class of deep-ultraviolet nonlinear optical (DUV NLO) crystals that promise to be less toxic and have better performance than the
ENVIRONMENT
step. The indolenine precursor and its derivatives are structural isomers, so the cascades in effect are multistep rearrangements. With U-protein enzymes now in hand—they can be isolated from cyanobacteria—Liu believes it will be easier to synthesize diverse members of this family of bioactive natural products in the laboratory.—STU BORMAN
CHEMICAL COMMUNICATION
▸ Bumblebees leave foot odor on flowers Not only do bumblebees have smelly feet, but the insects also leave an imprint of their foot odor on flowers they visit. In fact, the hydrocarbon chemical signature is so strong that it can be detected for about 24 hours after being deposited. A team of researchers led by Richard F. Pearce of the University of Bristol reports that bumblebees visiting flowers can also decipher whether the left-
NANOMATERIALS
Nanostructures lift the fog To state the obvious, water makes things wet. What may not be so obvious, however, is that even superhydrophobic surfaces can succumb to water’s propensity to moisten. Researchers often fashion tiny hydrophobic bumps, pillars, and protrusions on these surfaces to help keep water away. But they’ve found that fine fog droplets can still slip into the spaces between nanostructures and accumulate into larger drops to wet surfaces. So researchers led by David Quéré of ESPCI Paris launched a systematic 200 nm investigation into the design of nanotextured hydrophobic surfaces that get around the fogging problem (Nat. Mater. 2017, DOI: 10.1038/ nmat4868). By plasma etching self-assembled Hydrophobic nanocones pinch the bottom of fog thin films of a polystydroplets, creating enough pressure to eject the rene-poly(methyl methwater from the surface and prevent fogging. acrylate) block copolymer, the team created arrays of rods or cones, depending on the etching conditions. The researchers then coated the arrays with hydrophobic fluorinated chlorosilane groups. Water droplets initially grew on all the textured surfaces, but substrates with tightly packed cones eventually kicked the droplets off. The shape and proximity of the cones caused growing droplets to contort dramatically, which generated enough pressure to expel water from the surface with unprecedented efficiency, Quéré explains. He adds that such droplet departure has been observed previously, but “what seems unique with nanocones is the rate of departure is much, much larger than previously reported.” Understanding this behavior could help scientists design better antifogging windshields, mirrors, and solar cells, the researchers say.—MATT DAVENPORT
have been able to show that bumblebees can distinguish their odor from that of their nest mates, Pearce notes.—SARAH EVERTS
CREDIT: NAT. MAT E R. (CONES); SHUTTERSTOCK (BEE)
When bumblebees land on a flower, they leave behind their foot odor, which stems in part from (Z)-9-tricosene (shown). over foot funk is their own, a nest mate’s, or that of an entirely unknown bumblebee. The researchers think being able to distinguish these odor prints could prevent bees from making redundant visits to the same nectar source (Sci. Rep. 2017, DOI: 10.1038/srep43872). Bumblebees aren’t the only insects to leave behind smelly foot residues as they go about their day: Wasps, termites, and ants also secrete mixtures of hydrocarbons from their feet that give each individual its own personal aroma. The secretions also help with adhesion and with avoiding desiccation. For bumblebees, their signatures often include (Z)-9-tricosene and other long-chain hydrocarbons, and the relative concentration of these components uniquely identifies an individual. The new findings represent the first time researchers
acid (J. Am. Chem. Soc. 2017, DOI: 10.1021/ jacs.6b12360). Gandelman’s group had previously studied a triazolium salt and found it to be an analog of imidazole-based N-heterocyclic carbenes, including the ability to CHEMICAL BONDING serve as a ligand for transition metals. The central nitrogen of the saturated N–N–N triazolium unit in the molecule can accept electron density from a metal into a vacant p orbital, even though it weakly donates its lone pair of electrons residing in an sp2-type Lewis acids and bases are one of chemistry’s orbital to the metal. With that information fundamental concepts, depicting a molein hand, the team decided to treat various cule’s ability to accept an electron pair from triazolium compounds with different Lewis a partner molecule or to donate an electron bases such as phosphides, phosphines, and pair to a partner, respectively. For example, carbanions and found that the nitrogen-cenelectron-rich nitrogen-centered moletered molecules functioned as the Lewis acid cules such as ammonia function as Lewis partner. Gandelman and coworkers think bases. Mark Gandelman of these new nitrogen-based CH3 Technion—Israel Institute of Lewis acids could join other : Base Technology and his group have well-established Lewis acids N found a situation in which they based on boron, phosphorus, N+ : can turn that donor-acceptor aluminum, and tin and serve in N reactivity around, so that reactive frustrated Lewis pairs CH3 a nitrogen-centered molor other types of catalysts.— ecule functions as a Lewis Triazolium Lewis acid STEVE RITTER
▸ Nitrogen Lewis acids unveiled
MARCH 13, 2017 | CEN.ACS.ORG | C&EN
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