Science Concentrates SYNTHETIC BIOLOGY NANOMATERIALS
CREDIT: NAT. CHEM. BIOL. (PLATE OF BACTERIA); SCI. ADV. ( F LOW ER )
▸ Protected carbon dots keep on fluorescing A new material composed of carbon dots embedded in zeolites, with the muchsought-after property of delayed fluorescence, fluoresces longer at ambient temperature and pressure than any such material, scientists report (Sci. Adv. 2017, DOI: 10.1126/sciadv.1603171). So-called thermally activated delayed fluorescence (TADF) materials have gained popularity in recent years, as their high quantum efficiency makes them useful for numerous applications, such as sensors and flat-panel displays. Carbon dots, which are less than 10 nm in size, are popular candidates for TADF materials because they are nontoxic, biocompatible, and stable. Blue flower petals made Light excites from carbon dots in a electrons in zeolite matrix fluoresce the carbon substantially longer dots to tripthan a green stem made let states, from a benzyl dye. with delayed fluorescence occurring as electrons cross over to the singlet state. However, outside influences such as atmospheric oxygen can absorb the electrons’ energy before they have a chance to emit photons. So Jiyang Li, Jihong Yu, Jiancong Liu, and their colleagues at Jilin University protected the carbon dots by embedding them in a zeolite matrix. The result was a material with a fluorescence lifetime of up to 350 milliseconds, which far exceeds the several-millisecond maximum lifetimes of other materials.—ELIZABETH WILSON
CATALYSIS
▸ Antimony ligand helps turn on platinum reactive site Homogeneous transition-metal complexes typically need a jump start to become catalytically active. One strategy chemists employ is to use a silver salt or a Lewis acid activator such as a boron compound to pull
Paint by microbe If this image (shown) hung in an art gallery, the plaque describing it wouldn’t read “paint on canvas.” Instead, it would say, “Escherichia coli on agar plate.” Synthetic biologists engineered these bacteria such that when the scientists projected a red, green, and blue image onto a mat of the microbes, the cells produced red, green, and blue pigments in the pattern of the original image (Nat. Chem. Biol. 2017, DOI: 10.1038/ nchembio.2390). This bacterial artwork serves as a demonstration of a genetic circuit the researchers designed to enable them to use various wavelengths of light to control the expression of multiple genes in the microbes. Such a circuit could allow researchers better control over the Researchers projected an image (inset) onto production of complex a plate of engineered bacteria, which then molecules or materials recreated the image with red, green, and blue with engineered bactepigments. ria, says Christopher A. Voigt of Massachusetts Institute of Technology, who led the work. The circuit consists of 18 genes, including those for the protein sensors of the three colors of light, a biological circuit breaker that ensures none of the signals in the circuit overwhelms the cell, and enzymes to produce the three pigments. Voigt’s team designed a similar circuit to use the three light wavelengths to control three enzymes in a metabolic pathway in E. coli.—MICHAEL TORRICE
off and sequester an anionic ligand from the complexes, the researchers found that ancatalyst metal. Di You and François P. Gabtimony’s ability to adopt variable coordinabaï of Texas A&M University have designed a tion numbers, a property the Gabbaï group new strategy for ligand abstraction by buildcalls coordination noninnocence, enables ing an antimony Lewis acidic site directly antimony to shed loosely bound anionic into a platinum catalyst’s architecture, form- ligands such as triflate and add stronger ing a self-activating catalyst system (J. Am. coordinating anions such as chloride. In Chem. Soc. 2017, DOI: 10.1021/jacs.7b03287). the new antimony-platinum complex, this Gabbaï’s group is known for synthesizing ability is triggered when a nucleophilic subelectron-deficient main-group compounds strate approaches the electrophilic platinum and studying their reactive site. Subseanion-binding and When approached by a nucleophilic quent spontaneous redox properties. substrate such as an alkyne, antimony chloride migration from While investigating abstracts a chloride ligand to platinum to antimony antimony-platinum unmask platinum so that it becomes unmasks platinum, catalytically active (Ph = phenyl, leaving it exposed and OTf = triflate ). catalytically active. The Lewis researchers found that acidic site the antimony-platinum Cl OTf 2+ complex can mediate Sb Sb enyne cyclization and hydroarylation of propTfO argyl aryl ethers without Ph2P Pt PPh2 Ph2P Pt PPh2 the need for adding a Cl chloride abstracting reSubstrate Substrate agent.—STEVE RITTER MAY 29, 2017 | CEN.ACS.ORG | C&EN
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