Science Concentrates POLYMERS
▸ Polymeric film mimics skin wrinkling
Like human skin that wrinkles upon prolonged exposure to water, a polymeric material reversibly develops microscopic wrinkles. humidity. To make the materials, Songshan Zeng, Luyi Sun, and coworkers prepared bilayers consisting of a stiff hydrophilic film of polyvinyl alcohol (PVA) tightly bound to a flexible hydrophobic film of polydimethylsiloxane. By varying the degree of PVA cross-linking and the thickness of the layers, the team designed samples that wrinkled in distinct ways because of moisture-induced stiffening and swelling. One of the materials wrinkled in a fully reversible way when humidified and later dried. Another material wrinkled but did not unwrinkle when dried. A third material wrinkled, then unwrinkled when it was dried but did not rewrinkle when humidified.—MITCH JACOBY
BIOCHEMISTRY
▸ Calcium transport enzyme rocks Proteins that pump ions across membranes are essential to proper function of cells. Transmembrane calcium transporters, for
8
C&EN | CEN.ACS.ORG | MAY 8, 2017
At night, the tobacco plant flowers release (E)-α-bergamotene to attract tobacco hawkmoth pollinators. During the day, the plant’s leaves produce the terpene to attract predators for the moth’s larvae that dine on the leaves.
(E)-𝛂-Bergamotene
BIOCHEMISTRY
One compound resolves two-part plant dilemma Relationships are often a complicated mix of good and bad. This reality of life is perfectly exemplified in the liaisons of the tobacco plant and the tobacco hawkmoth. The moth pollinates the plant, which helps the plant thrive. But the moth also lays eggs on the plant leaves, and those eggs produce larvae, which soon devour the plant leaves. To resolve this dilemma in an optimal way, the plant exploits clever chemistry and plant biology, according to a study (Curr. Biol. 2017, DOI: 10.1016/j.cub.2017.03.017). Researchers led by Shuqing Xu of the Max Planck Institute for Chemical Ecology found that the solution comes courtesy of a volatile compound called (E)-α-bergamotene. At night, when the nocturnal moth is out and about, the plant’s flowers release (E)-α-bergamotene. The molecule activates neurons in the insect’s proboscis, inspiring the moth to stay longer at a flower, which increases the likelihood of pollination. During the day, when the adults are resting but the moth’s larvae are actively searching for a hearty meal, production of (E)-α-bergamotene shifts to the plant’s leaves. That switch attracts predators that feed on the larvae and eggs, protecting the plant. By optimally coordinating the timing and location of (E)-α-bergamotene biosynthesis, the plant has evolved a one-compound chemical strategy that improves pollination and defends against herbivores.—SARAH EVERTS
example, are key to muscle contraction, among other activities. But proteins embedded in phospholipid membranes are difficult to crystallize and study structurally. A contrast X-ray technique has now enabled a new view of a Ca2+-ATPase pump, demonstrating that the pump’s reaction cycle involves a rocking motion facilitated by amino acid-phospholipid interactions (Nature 2017, DOI: 10.1038/ nature22357). A team led by the University of Tokyo’s Chikashi Toyoshima studied Ca2+-ATPase, also known as SERCA1, in a phospholipid bilayer by placing crystals in contrast media of different concentrations
Interactions between Ca2+-ATPase arginine and lysine residues and phospholipid head groups help hold the enzyme (green) in the membrane as it tilts back and forth during the pump cycle. and comparing the resulting X-ray diffraction intensities. They found that the protein tilts back and forth as it pumps calcium through the membrane, staying anchored in place through interactions between positively charged arginine and lysine residues and negatively charged phospholipid head groups on either side of the membrane. The interactions allow for
CREDIT: DANNY KESSLER/MPI CHEM. ECOL. (PLANT NIGHT SHOT); ANDRÉ KESSLER/CORNELL U. (PLANT DAY SHOT); A DV. M AT ER . (WRINKLES); YOSHIYUKI NORIMATSU & CHIKASHI TOYOSHIMA/U. TOKYO (RIBBON)
Stay in the bathtub or pool a little too long or keep a water-soaked bandage wrapped on your finger for an extended period, and your skin will look like a shriveled-up prune. That water-induced wrinkling process has inspired materials scientists at the University of Connecticut to design a series of polymeric materials that wrinkle in a controllable way upon exposure to humidity (Adv. Mater. 2017, DOI: 10.1002/ adma.201700828). The advance deepens understanding of wrinkling dynamics and may lead to moisture sensors, optical coatings, light diffusers, and other devices in which functions are triggered by changes in
large protein movements while keeping hydrophobic residues within the bilayer. A belt of hydrophobic tryptophan residues may serve to sense the water-lipid boundary, and a trio of two tryptophans and a lysine-phospholipid interaction may serve as a pivot point for tilting.—JYLLIAN KEMSLEY
MATERIALS
▸ Phospholipids self-assemble into cuboid vesicles When lipids self-assemble as vesicles, they typically form spheres because that shape minimizes surface tension. Only a few nonspherical systems have been made to
CREDIT: ANDREAS ZUMBUEHL/U. FRIBOURG (CUBE MODELS); CHEMSUSCHEM (SCHEME)
Cuboid phospholipid vesicles could be used for mechano-responsive drug delivery. date, and many of those systems require templates to scaffold the structure. Now, a team led by Andreas Zumbuehl of the University of Fribourg reports a 1,2-diamidophospholipid that self-assembles into cube-shaped vesicles without a scaffold (Angew. Chem. Int. Ed. 2017, DOI: 10.1002/ anie.201701634). Hydrogen bonding between amide groups in the lipid leads to rigid membranes. Wide-angle X-ray scattering measurements suggest that the membrane packs in a herringbone pattern, the tightest bilayer packing known. Because of their stiffness, the membranes must be heated above their melting temperature, where they are in a fluid state, to form vesicles. When the vesicles are then cooled below their melting temperature, they adopt a cubic shape that maximizes flat surfaces and minimizes edges. The researchers want to use the cubes to help design drug delivery devices that respond to mechanical triggers. “The cubes themselves are probably too frail for this purpose because of their very long defect lines along the edges,” Zumbuehl says. “But they’ve taught us a lot about the physics needed for a next-generation mechano-responsive drug delivery container.”—CELIA ARNAUD
BIOCHEMISTRY
Chemical mimics endurance training in mice “Hitting the wall” is a familiar experience to people who push their bodies to the limit during a marathon or even in an unexpected bout of prolonged exertion. Biochemically speaking, this means the body’s tissues have used up their reserves of glucose. Exercise typically improves performance by teaching F3C the body to oxidize fat for energy and to N preserve glucose. But how that process works has remained unclear. A team S S of researchers led by Michael Downes and Ronald M. Evans of the Salk Institute for Biological Studies has now determined that one of the proteins in muscle that orchestrates this improved endurance is a transcription factor called PPARδ (Cell Metab. 2017, DOI: GW 501516 10.1016/j.cmet.2017.04.006). The team also found that activating PPARδ with a compound called GW501516 enhanced endurance in mice without any training. Even “couch-potato” mice were able to run an additional 100 minutes before they hit the wall if they were given a dose of GW501516. Whether the drug-induced enhancement occurs in humans is still to be determined, but the compound has already been touted on the black market as a performance enhancer and it was banned by the World Anti-Doping Agency in 2013.—SARAH EVERTS
BIOBASED CHEMICALS
▸ Enzymatic sulfation helps solve lignin’s solubility problem Lignin produced by plants is nature’s greatest source of aromatic compounds, and it’s readily available as a by-product of the pulp and paper industry. It seems natural that chemists would want to take advantage of the material as a source of aromatics to reduce reliance on coal, oil, and natural gas. One problem is that lignin’s aromatics are locked up in complex insoluble polymeric chains. Gadi Rothenberg, Ron Wever, and coworkers of the University of Amsterdam have developed an enzymatic process to selectively add hydrophilic sulfate groups to lignin’s many phenol rings to make the
OH Aryl sulfotransferase
+
NO2 Lignin
O
material easier to dissolve for processing (ChemSusChem 2017, DOI: 10.1002/ cssc.201700376). Wever’s group previously found that a bacterial aryl sulfotransferase enzyme can take sulfate groups from p-nitrophenylsulfate and add them to hydroxyl groups of various phenol compounds. The joint team has now extended the chemistry to various types of lignins. The researchers show that the process is selective for phenolic groups, leaving aliphatic hydroxyl groups in lignin side chains untouched. The resulting sulfated lignins dissolve easily in mildly alkaline solutions, with the increase in solubility visible to the naked eye and traceable by UV-Vis and NMR spectroscopy. The researchers note that the new method improves on prior lignin sulfating processes as well as current approaches that use caustic solutions, ionic liquids, or supercritical solvents, which are relatively costly and generate significant waste.—STEVE RITTER
SO3Na +
OH
O
Sulfating agent
NO2 Lignin dissolved in water MAY 8, 2017 | CEN.ACS.ORG | C&EN
9
