findings broaden understanding of atmospheric electrical phenomena and reveal a previously unrecognized natural source of radioactive isotopes on Earth.—MITCH
JACOBY
CATALYSIS
▸ Uranium doubles up as a catalyst
C R E D I T: COU RTESY O F ST E P H E N L I D D LE ( 3 -D MO D E L) ; A DA PT ED FRO M N AT. CH E M . (M OTO R M O L ECU L ES); CAS E Y K E N N E DY (CRAN B E R R I ES )
Reversible, two-electron redox processes in which a substrate is added and subsequently eliminated from a transition metal are a defining feature of most catalytic cycles. This behavior is typically unheard of, though, when it comes to lanthanide and actinide metals. The f-block metals are used as catalysts, but they tend to exhibit irreversible one- or multielectron oxidation or reduction steps, and the complete redox sequence hasn’t been observed in one re-
MOLECULAR MACHINES
Motor molecules made into muscles Chemists have gotten a lot of mileage out of the Nobel Prize-winning, light-activated motor molecules invented in Ben L. Feringa’s lab at the University of Groningen. Feringa has used them to create molecule-sized cars that scoot along a surface, and others have incorporated them into polymers or used them to drill holes in cancer cells (see page 24). Feringa’s group has now managed to get these molecule-sized machines to flex some muscle. His team created a water-soluble version of the motor that assembles into fibers. In the presence of calcium ions, these fibers organize into macroscale strings made mostly of water that flex in response to ultraviolet light. They can even lift a small weight: a 400-mg piece of paper (Nat. Chem. 2017, DOI: 10.1038/nchem.2887). As with previous versions of Feringa’s motors, these molecules rotate via isomerization around a double bond when hit with UV light. The motor molecules pack closely together in the self-assembled fibers and expand a little bit in the presence of the light, causing the string to bend. “You amplify a tiny motion from the molecular level all the way up to the macroscopic level,” Feringa notes. While others have made artificial muscles using molecular machines covalently linked to polymers, this is the first time that such muscular systems have been assembled entirely from small molecules.—BETHANY HALFORD
but the findings provide a pathway to discovering new lanthanide and actinide catalysts—for example, to synthesize aniline derivatives.—STEVE RITTER
POLLUTION This dimeric uranium(V) complex, joined at the center by azobenzene, provides the best evidence yet for transition-metal redox behavior in an f-block element. action system. Researchers led by Stephen T. Liddle of the University of Manchester and Laurent Maron of the University of Toulouse have now found evidence that a uranium complex can satisfy all the criteria of classical single-metal, two-electron oxidative addition-reductive elimination, and they make a case that uranium can mimic traditional transition-metal catalysis (Nat. Commun. 2017, DOI: 10.1038/s41467-01701363-0). The researchers added azobenzene to a uranium(III) triamide complex they previously reported to form a dimeric uranium(V) imido complex, which readily expels azobenzene back out upon heating. The researchers confirmed the oxidation and reduction steps using a combination of structural, spectroscopic, magnetic, and computational studies. The reaction sequence is not yet optimized, Liddle says,
▸ To trap fertilizer in cranberry bogs, just add salt Phosphorus from fertilizer can readily escape farms by hitching a ride on sediment particles suspended in water runoff. Cranberry bogs, in which farmers use water to help harvest the scarlet berries, are no different. Scientists with USDA and the University of Massachusetts Cranberry Station are working to keep phosphorus in cranberry bogs to reduce the amount of the nutrient in water and limit harmful algal blooms downstream. The team
reports that aluminum sulfate treatment can trap phosphorus in the sediment of irrigation ponds and cranberry bogs, preventing it from draining away (J. Environ. Qual. 2017, DOI: 10.2134/jeq2017.04.0134). The researchers, led by Casey D. Kennedy of USDA’s Agricultural Research Service, tested the ability of various salts to remove phosphorus from pond water. Certain salts can neutralize negative charges on sediment particles, causing them to clump together and settle out of the water. This process locks residual phosphorus away so it’s unavailable to plants and algae. Lab experiments showed that aluminum sulfate, compared with iron and calcium salts, most effectively binds phosphorus at low concentrations (5 to 15 mg/L). To test the feasibility of using aluminum sulfate on cranberry farms, the scientists dispersed 15 mg/L aluminum sulfate into an irrigation pond and a former cranberry bog. Aluminum sulfate treatment worked best in the shallow waters of the former cranberry bog, removing 94% of the phosphorus from the water compared with 78% from the irrigation pond.—EMMA HIOLSKI
Farmers harvest cranberries by flooding fields, but the water can carry excess phosphorus downstream and pollute waterways. DECEMBER 11/18, 2017 | CEN.ACS.ORG | C&EN
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