Chemistry that delighted us in 2020

Black as the void

In the darkest depths of the ocean, bioluminescence can make a creature stand out like a sore thumb—or tasty snack. This year, researchers discovered that deep-sea fish have evolved a way to blend into the void using ultrablack skin. This skin contains a carefully arranged layer of melanin granules that reflects less than 0.5% of the light that shines on it, according to a study led by Karen Osborn of the Smithsonian National Museum of Natural History (Curr. Biol. 2020, DOI: 10.1016/j.cub.2020.06.044). Ultrablack skin protects fish like the Pacific blackdragon (Idiacanthus antrostomus) not only from being caught in the spotlights of predators but also from being sold out by its own bioluminescent lure. Further, the adaptation may help some fish block the glow of bioluminescent prey they’ve eaten, which might otherwise shine through their bellies. This discovery could help scientists design new, ultrablack materials.

Nanoscale chains

With the precision of a tiny blacksmith, a team led by Shiki Yagai at Chiba University has forged nanoscale chains from a simple monomer using nothing but noncovalent interactions (Nature 2020, DOI: 10.1038/s41586-020-2445-z). This monomer self-assembles through hydrogen bonds to form six-membered, snowflake-like macrocycles. As the snowflakes stack on top of one another, they create twisting coils that can curve into closed rings. The researchers were surprised to find that those rings interlock under the right solvent conditions, forming chains with up to 22 links. This discovery could open the door for new kinds of interlocking supramolecular assemblies.

Gregarious grasshoppers

Swarms of locusts have been known to block the sun when they descend on crops. This year, researchers led by Xianhui Wang and Le Kang of the Chinese Academy of Sciences have discovered the small-molecule signal that tells these insects to flock together (Nature 2020, DOI: 10.1038/s41586-020-2610-4). After analyzing a brew of 35 volatile molecules emitted by Locusta migratoria, the team found that 4-vinylanisole is the pheromone responsible for the swarming behavior. The researchers also identified the olfactory receptor in the insects, called OR35, that recognizes this small molecule. The team hopes that studying this newly discovered pheromone-receptor pair can lead to molecular methods for farmers to lure the ravenous locusts away from their precious harvests.

The world’s brightest fluorescent material

Most fluorescent dyes lose their luster when locked in solid materials. That’s because when the dye molecules are packed together, they prevent one another from emitting photons. This year, a research team led by Amar H. Flood of Indiana University Bloomington and Bo W. Laursen of the University of Copenhagen designed a new material architecture to give these molecules space. Using a neutral macrocycle known as a cyanostar, the team separated cationic fluorescent dye molecules while sequestering their counterions (Chem 2020, DOI: 10.1016/j.chempr.2020.06.029). The cyanostar-fluorophore complex can be crystallized and incorporated into polymers and resins. The team found that this technique works for any cationic fluorophore as long as its counteranion is small. The team’s materials, which are produced by 3-D printing, exhibit the brightest fluorescence reported to date on the basis of volume.

Signals from beyond the grave

When bacteria swarm, they move in collective motion and turn on mechanisms to resist antibiotics. This year, Souvik Bhattacharyya, David M. Walker, and Rasika M. Harshey of the University of Texas at Austin discovered that even dead Escherichia coli participate in the swarm (Nat. Commun. 2020, DOI: 10.1038/s41467-020-17709-0). The team found that dead E. coli release a protein called AcrA, which is part of a TolC pump that the bacteria use to expel antibiotics from the cell. When TolC proteins on the surface of living E. coli cells interact with the AcrA signal from dead E. coli, the swarm takes evasive measures to avoid a potential antibiotic threat. As a result, the death of a subpopulation of bacteria could benefit the swarm as a whole.

Metallic-blue berries

A research team led by Silvia Vignolini at the University of Cambridge discovered a new form of structural color in a metallic-blue berry (Curr. Biol. 2020, DOI: 10.1016/j.cub.2020.07.005). The berries of Viburnum tinus (shown), a popular garden plant in Europe, owe their color to layers of globular lipids that scatter light on the fruit’s surface. This is the first time lipids have been identified as the source of structural color, but the researchers suspect this strategy is more common than previously thought. Although it is unclear what benefit this metallic hue bestows on the plant, the researchers are trying to determine how V. tinus controls the formation and arrangement of these lipid globules in order to design similar structures for new synthetic materials.