Science Concentrates ELECTRONIC MATERIALS
▸ Cell-based hormone replacement Women whose ovaries stop functioning because of either menopause or disease can experience health effects that go beyond the loss of fertility, including osteoporosis and obesity. The standard treatment—hormone replacement with estrogen alone or in combination with progestin—can mitigate those problems. But the treatment comes with other risks, including an increased chance of breast cancer and heart disease. A team led by Emmanuel C. Opara of Wake Forest School of Medicine is developing bioengineered polymeric capsules that mimic ovarian follicles for use as a
Electric eel inspires soft power source The knifefish Electrophorus electricus, better known as the electric This soft power source combines four types of hydrogel. eel, can generate electricity to stun its prey thanks to specialized organs that generate power via ion flux—no batteries required. The structure of these organs provided a jolt of inspiration to researchers led by Michael Mayer of the Adolphe Merkle Institute at the University of Fribourg, who wanted to create a soft power source. The electric eel’s organs contain thousands of alternating compartments containing either potassium or sodium ions separated by membranes that keep the ions apart. When the knifefish charges up, the membranes let the ions flow, creating a burst of power. To create ion gradients in their system, Mayer and colleagues used three-dimensional printing to pattern a substrate with alternating spots of hydrogels loaded with either sodium chloride or pure water (shown in red and blue, respectively). On a different substrate, they dotted cation-selective and anion-selective hydrogels (shown in green and yellow, respectively). When overlaid, the system of dots creates a conductive pathway that can generate up to 110 V (Nature 2017, DOI: 10.1038/ nature24670). The researchers note that because the materials are biocompatible, they have the potential to power implantable medical devices, such as pacemakers. “To get there, we are looking for talented Ph.D. students and postdocs,” Mayer says.—BETHANY HALFORD
This ovarian-follicle mimic delivers cellbased hormone replacement therapy that could replace current drug therapies at lower doses and with fewer side effects.
the hormone pellets or in rats whose ovaries were still intact.—CELIA ARNAUD
cell-based method of hormone replacement (Nat. Commun. 2017, DOI: 10.1038/s41467017-01851-3). To make these artificial ovaries, the researchers encapsulate two types of hormone-producing ovarian cells—granulosa and theca cells—in separate layers of cross-linked alginate (a polysaccharide) with layers of poly-l-ornithine between. They tested the capsules by implanting them in rats whose ovaries had been removed and comparing the performance with rats whose ovaries had been removed and treated using hormone-containing pellets at high and low doses of estrogen with or without progestin. After 90 days, rats that received the cell-based therapy had similar body weight, fat percentage, bone mineral density, and uterine morphology as rats with intact ovaries. These positive effects were achieved with hormone levels in the blood that were lower in rats receiving the cell-based therapy than in rats receiving
NUCLEAR CHEMISTRY
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C&EN | CEN.ACS.ORG | DECEMBER 11/18, 2017
▸ Lightning triggers nuclear reactions Nearly 100 years ago, physicists proposed that high-energy processes occurring during thunderstorms might trigger nuclear reactions. But limitations in detector technology and difficulties in making measurements during thunderstorms have prevented researchers from recording direct experimental evidence of such nuclear reactions—until now. On Feb. 6, a team led by Teruaki Enoto of Kyoto University tracked two cloud-to-ground lightning strikes during a thunderstorm over the coast of the Sea of Japan. Using data recorded at monitoring stations near the lightning strikes, which include time- and energy-correlated signals of γ rays, neu-
trons, and positrons, the team concludes that it observed γ-ray-induced photonuclear reactions (Nature 2017, DOI: 10.1038/ nature24630). Specifically, the researchers detected telltale signs that γ rays, which are produced in thunderclouds as intense electric fields drive high-energy electrons into airborne molecules, can knock a neutron out of an 14N nucleus, creating an 13N isotope. That isotope is unstable: It decays into a neutrino, Lightninga positron, and a generated γ rays stable 13C nucleus. can trigger nuclear Upon collision with reactions in an electron in an atmospheric atmospheric molmolecules. ecule, the positron and electron undergo annihilation and produce a pair of γ rays with a characteristic energy of 0.511 MeV. The researchers note that related processes generate 14C and 15N isotopes. These
CR E D I T: T H O MAS S C HRO ED ER /A N I RVAN GU H A (SO F T- P OW E R S O U RCE ); N AT. CO M M U N . (DI AG RA M ); LYO H A1 23/ W I K I M E DI A COM M ON S (LI GH T N I N G)
BIOTECHNOLOGY
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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