Science Concentrates SYNTHESIS MATERIALS
▸ Octopus-inspired robot skin goes 3-D
Chemists build a triple norbornane
Engineers have used the fluid and flexible nature of the octopus as inspiration for designing soft-bodied robots and artificial skins that change color or glow. Now, researchers have captured another facet of octopus camouflage: three-dimensional skin texturing. Cephalopods such as octopuses and cuttlefish raise specialized bumps on their skin, called papillae, to blend into their surroundings. One papilla can form a variety of shapes, such as a cone or trilobe, depending on how the muscles within it are arranged. To create an artificial skin that mimics this 3-D camouflage strategy, a team led by Robert F. Shepherd of Cornell University embedded laser-cut
As molecular explorers, chemists often venture out into “chemical space” to see what strange new discoveries they can make. To assist in these efforts, researchers have devised algorithms that take a prescribed set of elements and number of atoms and work through all the possible combinations leading to stable molecules that are synthetically feasible. Using the GDB-11 database, which constructs molecules containing C, N, O, or F and containing up to 11 framework atoms, a team led by Marcel Mayor of the University of Basel decided to zoom in on polycyclic hydrocarbons lacking three- or four-membered rings. This structural SO2C6H5 CH3O Cl motif is sometimes O CH3O found in natural + products that have O O potential as drug canOCH CH O 3 3 O didates. Among the 124 molecules that C6H5O2S popped up in the data-
one day make skins that form multiple shapes.—EMMA HIOLSKI
A 22- by 22-cm silicone membrane (top) inflates to form river rock shapes (bottom). fiber mesh into a mold containing a silicone liquid. The mesh—a common nonwoven nylon embroidery stabilizer—provides structural support to cured silicone when the material is inflated and, depending on the laser-cut pattern, helps create a targeted shape (Science 2017, DOI: 10.1126/science. aan5627). The engineers used an algorithm, developed by lead author James H. Pikul, now at the University of Pennsylvania, to determine which pattern to cut in the mesh and created shapes including cones, river rocks, succulent plants, and topographical maps. These skins could help disguise robots or even serve as customizable shipping material. Though each skin can form only one predesigned shape, Shepherd says replacing the mesh with inflatable tubing, or using a voltage gradient instead of air, could
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C&EN | CEN.ACS.ORG | OCTOBER 16, 2017
CHEMICAL SENSING
▸ Electronic ring detects chemical threats The field of wearable sensors is booming. Many people, for example, use Fitbits on their wrists to track their physical activity. Less attention has been devoted to wearables for defense applications, but Joseph Wang and coworkers at the University of California, San Diego, have now taken a step toward addressing that gap (ACS Sens. 2017, DOI: 10.1021/ acssensors.7b00603). The researchers designed,
constructed, and tested a battery-powered ring that monitors for explosives and nerve agents in air and liquids and sends wireless alerts, to a cell phone for instance, when it finds them. The outer surface of the ring has printed electrodes on it. A semisolid agarose hydrogel on the surface promotes analyte diffusion to the electrodes, which are linked to miniaturized electronics inside the device that interpret the electrochemical signals and transmit the data. The ring uses chronoamperometry and fast square-wave voltammetry to monitor nitroaromatic and peroxide explosives and organophosphate nerve agents. The researchers believe the device’s capabilities can be extended to other hazardous agents. “The miniaturization and integration of the electronics and sen-
With this ring, I thee protect: The sensors are capable of monitoring for explosive residues and chemical nerve agents.
C R E D I T: S CI E NC E ( RO CKS ) ; COU RTESY OF JO S EP H WA NG ( R I N G )
base search, only three had no real-world Trinorbornane counterparts. One of these 9 steps compounds, an intricate symmetrical saturated C11H16 7% overall yield molecule, was “particularly appealing and eye catching,” so the researchers decided to try to make it (Chem. Commun. 2017, DOI: 10.1039/c7cc06273g). The compound’s scaffold consists of two norbornane units that share a pair of neighboring edges, an arrangement that coincidentally results in a third norbornane subunit. Using a total synthesis strategy similar to the way chemists go about preparing natural products, the researchers succeeded in making a racemic mixture of the chiral compound, which they have named trinorbornane, in nine steps with 7% overall yield.—STEVE RITTER
sors in a simple, compact, autonomous, and wirelessly connected unit is, from my perspective, the most remarkable aspect of the study,” comments nanosensors group leader Francisco Andrade of Rovira i Virgili University. “The device could also be attached to a wristband or hat or Velcroed to a garment,” he suggests.—STU BORMAN
TISSUE ENGINEERING
▸ Intestinal grafts grown from stem cells Gastrointestinal disorders such as Crohn’s disease can lead to a condition known as short bowel syndrome (SBS) in which a significant portion of a person’s small intestine is no longer capable of absorbing nutrients. Intestinal grafts to supplement the remaining small intestine could help restore this lost function. A team led by Harald C. Ott of Massachusetts General Hospital has grown functional intestinal tissue by seeding scaf-
C R E D I T: NAT. M AT E R . ( MO F) ; K E NTA RO KI TA N O ( IN TEST I N E) ; S C I . ADV ( CATALYST)
A small-intestine scaffold with the original cells removed has been repopulated with human-stem-cellderived endothelial cells (green) and with blood vessel cells (red). The overall length of the segment is 4 cm. folds formed from rat small intestines with human pluripotent stem cells (Nat. Commun. 2017, DOI: 10.1038/s41467-017-00779-y). The researchers remove all cells from a segment of rat small intestine to form a scaffold that retains the extracellular architecture of the original tissue. They direct the human stem cells to differentiate into intestinal progenitor cells and then use them to seed the scaffold. After two weeks in culture, the progenitor cells produce many of the cell types usually found in intestinal tissue. The researchers also add human umbilical cells to regrow blood vessels. The regenerated tissue is able to take up and transport glucose and fatty acids through the vasculature, with grafts transplanted into immunodeficient rats surviving and functioning for at least four weeks. Adding “bioengineered constructs as small segments of additional absorptive surface area could become a treatment option for nutrient intake in SBS in the future,” the researchers write.—CELIA ARNAUD
METAL-ORGANIC FRAMEWORKS
Liquid MOFs debut Metal-organic framework (MOF) compounds are a large family of porous crystalline materials composed of metal ions joined by organic linkers. Because of their extreme porosity, which can be tailored via A framework compound synthesis, MOFs are widely touted for their known as ZIF-4 (ball and stick) retains its structure and usefulness in gas separation, gas storage, porosity (yellow indicates void and catalysis. Liquid versions of these mavolume) in the liquid state. terials could be especially useful because liquids are often more robust and easier to process than crystalline powders. But porous liquids with molecular orderliness are almost unheard of. So a team led by Thomas D. Bennett of the University of Cambridge and François-Xavier Coudert of the French National Center for Scientific Research (who is a C&EN advisory board member) decided to try to make a liquid version of a MOF. They succeeded (Nat. Mater. 2017, DOI: 10.1038/nmat4998). On the basis of X-ray and neutron-scattering methods and various computational techniques, the researchers conclude that heating ZIF-4, which is composed of zinc imidazolate units, to 856 K causes the solid to melt but the high temperature does not cause bond cleavage and decomposition. The data indicate instead that the hot liquid retains the chemical configuration, coordinative bonding, and porosity of the crystal state. The liquid’s properties and structure differ from those of the glassy state obtained upon cooling the material. The team suggests that this type of processing might be used to shape MOFs at the macroscale by using the liquid as a transient state en route to forming a glass or recrystallized product.—MITCH JACOBY
CATALYSIS
▸ Bimetallic catalyst selectively converts CO2 to methanol Capturing CO2 from the air or from power-plant emissions and converting it to methanol sounds like a winning approach to curbing climate change. This strategy has the further benefit of being a potentially inexpensive way to make methanol, which is used as an industrial solvent and can double as a fuel or chemical reagent. But progress in driving CO2 hydrogenation to methanol has been slow going. Some of the proposed methods are energy intensive and costly. Others produce a low concentration of methanol mixed with by-products. One of the leading catalyst candidates, a copper-zinc oxide system, generates methanol with low selectivity, and more importantly, it fails quickly because catalyst particles coalesce and block access to catalytically active sites. A team led by Jijie Wang, Guanna Li, and Can Li of the Dalian Institute of
Chemical Physics reports that a “solid solution” of zinc oxide dispersed in a zirconium-oxide lattice is a more promising methanol synthesis catalyst (Sci. Adv. This bimetallic 2017, DOI: 10.1126/ catalyst sciadv.1701290). selectively The researchers find that ZnO-ZrO2, converts CO2 to methanol; Zr is which they prepare gray, Zn is blue, O by reacting zinc nitrate and zirconium is red. nitrate, generates methanol with up to 91% selectivity and retains its activity for more than 550 hours of reaction time, even in the presence of sulfur, a contaminant known to poison many solid catalysts. Computations indicate that the catalytic performance of the solid solution, which exceeds that of the individual components and physical mixtures of them, arises from the proximity of zinc and zirconium sites, which work in tandem to activate hydrogen.—MITCH JACOBY OCTOBER 16, 2017 | CEN.ACS.ORG | C&EN
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