Science Concentrates
When ignited, melamine, sugar, iron nitrate, and baking soda produce a snakelike, porous catalyst precursor.
POLLUTION
▸ Mutated enzyme breaks down plastic more efficiently
NANOMATERIALS
▸ Chiral gold nanoparticles The concept of chirality is a central one in chemistry. Chiral chemicals, in which two structures are mirror images that cannot be superimposed, include amino
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C&EN | CEN.ACS.ORG | APRIL 23, 2018
MATERIALS
Ancient reaction inspires method for making porous catalysts A recipe for a new electrocatalyst takes inspiration from an ancient reaction used in fireworks for making the wispy, elongated char known as pharaoh’s snakes. The newly reported version of the reaction converts a simple mix of ingredients to a high-surface-area, nanostructured catalyst for oxygen reduction in fuel cells and zinc-air batteries (ACS Appl. Mater. Interfaces 2018, DOI: 10.1021/acsami.7b16936). The carbon-, nitrogen-, and iron-containing material is much cheaper than the platinum or ruthenium dioxide it would replace. Ying Zhu of Beihang University was inspired by a YouTube video demonstrating the pharaoh’s snake: When a small mound of mercury thiocyanate powder is ignited, a series of reactions releases large amounts of gas, and the material forms long, highly porous, foamy ropes of carbon nitride that rise from the flames like snakes rearing their heads. Applying this principle to electrocatalysts, Zhu, Liming Dai of Case Western Reserve University, and colleagues ignited a combination of melamine (the nitrogen source), iron nitrate, sugar (the carbon source), and baking soda. The material grew into a snaky rope as it burned. After annealing at 1,000 °C, the researchers crushed the catalyst and used it in a methanol fuel cell and a zinc-air battery. The fuel cell operated at 0.9 volts, slightly better than platinum-catalyzed fuel cells. In the zinc-air battery, the new material functioned comparably to the standard, ruthenium dioxide. To be practical for fuel cells, the material must outperform platinum not just in alkaline solutions, as in these experiments, but also in acid. That’s a goal for future work, Dai says.—KATHERINE BOURZAC,
special to C&EN
acids and DNA. But chirality isn’t limited to molecules; chiral structures can exist
These nanoscale, chiral, gold structures were grown with L-cysteine (left) and D-cysteine (right).
on larger scales, such as nanoparticles, snail shells, and even galaxies. In the past, scientists have grown chiral nanoparticles using templates, such as DNA or proteins. Now, researchers led by Seoul National University’s Ki Tae Nam and Pohang Uni-
C R E D I T: ACS A P PL . M AT E R . I NT ER FAC ES ( FL A ME ) ; CO U RTESY O F KI TAE N AM (GO L D S E M )
Poly(ethylene terephthalate), or PET, is widely used in beverage bottles, clothing, packaging, and carpeting. After use, much of the plastic finds its way into landfills or becomes pollution, such as in the Great Pacific garbage patch. Used PET can be broken down chemically and reused, but the process is not widely employed because buying new PET is cheaper. Two years ago, a Japanese group found a bacterium that uses two enzymes to degrade and assimilate PET: PETase converts PET to mono(2-hydroxyethyl) terephthalic acid (MHET), and MHETase breaks down MHET into terephthalic acid and ethylene glycol. H. Lee Woodcock of the University of South Florida, John E. McGeehan O O of the University of Portsmouth, O O Gregg T. Beckham n of the National PET Renewable Energy Laboratory, and coworkers obtained high-resolution X-ray crystal structures of PETase. They also discovered that it degrades the emerging PET replacement polyethylene-2,5-furandicarboxylate (PEF), and they mutated the enzyme into a more efficient version (Proc. Natl. Acad. Sci. USA 2018, DOI: 10.1073/ pnas.1718804115). The native enzyme’s PET-degrading activity is too low for industrial use, but the mutant degrades PET about 20% more efficiently—suggesting that further optimization could lead to a commercial bioremediation system. After further enzyme engineering, the group plans to scale up this process to the pilot scale at NREL and work with industrial partners to take it beyond that point, Beckham says.—STU BORMAN
versity of Science & Technology’s Junsuk Rho report that sulfur-containing chiral molecules, such as cysteine or glutathione, can guide the growth of gold nanoparticles into chiral structures (Nature 2018, DOI: 10.1038/s41586-018-0034-1). The sulfur-containing molecules influence the growth rate of crystal facets within the gold, ultimately producing helicoid twists in the nanoparticles’ structures. The resulting particles are similar in size and can rotate polarized light. The researchers think the strategy could be used to make chiral nanoparticles for various applications, including plasmonic metamaterials, which have exotic optical properties and may be useful for sensing and imaging.—BETHANY HALFORD
MASS SPECTROMETRY
C R E D I T: S CI . A DV./C& E N ( S C R E EN GRA B) ; D. D E D OV E TS A N D S . D EV I L LE/ LSFC (E M U LS I O N )
▸ Measuring protein collision cross sections without ion mobility Because the collision cross section (CCS) of a protein is related to its overall shape, the measurement can provide information about various conformations the molecule adopts. A protein’s CCS, which relates its shape to the probability of interacting with gas molecules, is often determined using ion mobility separation in combination with quadrupole-timeof-flight mass spectrometry. Jennifer S. Brodbelt of the University of Texas, Austin, Alexander A. Makarov of Thermo Fisher Scientific, and coworkers now show that they can calculate protein CCS using an Orbitrap mass spectrometer without the need for extra hardware such as an ion mobility cell (Anal. Chem. 2018, DOI: 10.1021/acs.analchem.8b00724). They calculate the CCS from the decay rate of a particular mass-to-charge ratio (m/z) at a particular pressure. Because ions with different CCSs aren’t physically separated, the method provides an average value for all conformations of a given m/z, which means the method is best suited to protein charge states with just a single conformation. The researchers measured the CCS of multiple charge states of three proteins. CCSs obtained with an Orbitrap differed by less than 7% from those measured via ion mobility. Although the new method doesn’t completely replace ion mobility, it might enable more structural biologists to obtain conformational information.—CELIA
ARNAUD
MATERIALS
Slippery microgrooves help harvest fog Collecting moisture from air is a promising technique for providing water to the world’s arid regions. But the hydrophilic surfaces that are sometimes used for this purpose prefer to hold on to water rather than give it up for consumption. Scientists from Pennsylvania State University and the University of Texas, Dallas, have now developed a lubricated hydrophilic surface that both attracts and sheds water efficiently, thanks to parallel, microscopic grooves etched into the surface that promote drainage (Sci. Adv. 2018, DOI: 10.1126/sciadv. aaq0919). The microgrooves, which also provide increased surface area on which droplets can form, are coated with a thin layer of hydrophilic lubricant that is held in place by nanoscale roughness on the surface. In simulated foggy conditions provided by a conventional room humidifier, the grooved, lubricated surfaces outperformed a variety of other hydrophilic surface structures, as well as water-repellent surfaces, in both droplet formation and shedding. To see the water-harvesting surface in action, watch our video at cenm.ag/waterharvesting.—KERRI JANSEN
IMAGING
▸ Watching emulsions freeze As a liquid turns to a solid, getting a picture of events at the interface between what’s already solid and what’s still liquid
Confocal fluorescence microscopy captures the interface between the frozen (bottom) and not yet frozen parts of an emulsion of oil droplets (blue spheres) in water.
can be difficult. Sylvain Deville and Dmytro Dedovets at the Ceramic Synthesis & Functionalization Laboratory and Cécile Monteux of ESPCI Paris report an imaging approach based on confocal fluorescence microscopy that allows them to watch an emulsion of oil droplets in water as it freezes (Science 2018, DOI: 10.1126/science. aar4503). They use a temperature gradient to control where and how quickly the emulsion freezes and a flow cell to keep the interface within the focal plane of the microscope. Surfactants in the mixture stabilize the oil droplets and the images show that the surfactants help determine the microstructure of the resulting solid. The surfactants induce long-range interactions between the solidifying surface and the droplets that cause the droplets to be redistributed as the emulsion freezes. This redistribution—whether, for instance, the droplets form clumps or are spread out evenly—is what determines the solid’s microstructure. The imaging approach should be useful in many applications, including metal alloy formation, single-crystal growth, and food engineering. Deville plans to use the approach to study problems in cryopreservation of biological cells.—CELIA ARNAUD APRIL 23, 2018 | CEN.ACS.ORG | C&EN
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