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Biological Chemistry

Chemistry that delighted us in 2019

C&EN’s editors were entertained and amused this year by these discoveries

by Laura Howes
December 10, 2019 | A version of this story appeared in Volume 97, Issue 48


Electronic Jell-O

A round puck of Jell-O with a metal circuit on top.
Credit: Adv. Funct. Mater.
This Jell-O puck sports a complex, millimeter-sized pattern printed with a liquid-metal ink.

This wobbly Jell-O puck has a metallic circuit printed on it, thanks to a quirky metal developed by Andrew Martin, Martin Thuo, and coworkers at Iowa State University in 2019 (Adv. Funct. Mater. DOI: 10.1002/adfm.201903687). The bismuth-indium-tin alloy melts at 62 °C, but if made into droplets, it doesn’t completely solidify as it cools to room temperature. Instead, the droplets develop protective shells made of solid oxide that enable their metal centers to remain liquid at room temperature.

In some fun demonstrations, the team used these droplets to make an ink and then printed circuits on traditional and not-so-traditional surfaces, including rose petals and Jell-O. A quick tippety tap breaks the droplets’ oxide skins, allowing the metal to flow and solidify to form flexible circuits.


Revealing the tooth

Transparent pointy teeth protude from the mouth of a fish.
Credit: Matter
Dragonfish teeth are transparent in the deep sea.

The secrets of the dragonfish’s transparent teeth were revealed this year by a team led by Marc A. Meyers of the University of California San Diego (Matter 2019, DOI: 10.1016/j.matt.2019.05.010). A species of dragonfish, Aristostomias scintillans, lives around 500 m below the surface of the ocean and uses bioluminescence to lure its prey toward its spiky teeth. Unlucky prey don’t see the danger until it is too late because dragonfish teeth are transparent, thanks to nanoscale structures that don’t reflect or scatter light underwater.

Now that Meyers’s team knows the stealthy critter’s secret, the researchers plan to use the information to make new materials that we hope will be less terrifying.


Fungal fix for skunk stink

The chemical structure of pericosine.

Tomato juice, commercial treatments . . . you name it: nothing seems to get rid of that nasty skunk smell. But help may be on the way because of a discovery reported in 2019. Robert H. Cichewicz and colleagues at the University of Oklahoma found the secret to fighting skunk stink in the Alaskan soil (J. Nat. Prod. 2019, DOI: 10.1021/acs.jnatprod.9b00415).

Photograph of a skunk with its tail raised facing the camera. Overlaid is the structure of pericosine A.
Credit: Skeeze/Wikimedia Commons
Pericosine A neutralizes persistent, foul odors in skunk spray.

After a citizen science project identified the odd-looking natural product pericosine A a few years ago, Cichewicz’s team realized the compound might be able to break down the sulfur-containing compounds that give skunk spray its persistent stink. The researchers reacted pericosine A with various skunk thiols and found that it could convert the smelly compounds to odorless ones, resulting in thiol levels below human detection.

It’s just as well. Cichewicz, who once wafted his hand over a sample of pure skunk anal gland secretions, says that it was “the nasal equivalent of staring at the sun.”


Prehistoric parenting practices

A ceramic feeding vessel shaped like an animal.
Credit: Katharina Rebay-Salisbury
Analysis of adorable bottles like this one suggests they were used to wean babies in Europe long ago.

In 2019, 3,000-year-old pottery bottles provided chemical evidence for how parents weaned babies in prehistoric Europe. Julie Dunne at the University of Bristol took samples from small drinking bottles studied by Katharina Rebay-Salisbury’s team at the Institute for Oriental and European Archaeology. Dunne used gas chromatography and isotope analysis on the samples she collected and found evidence of animal milk still stored in the ancient pottery (Nature 2019, DOI: 10.1038/s41586-019-1572-x).

The advent of farming in Europe helped lead to a baby boom, and it was the bottles found in children’s graves that helped Dunne and Rebay-Salisbury bring ancient parenting back to life and find the first direct evidence that these long-ago parents fed their children ruminant milk.


A plate of sauerkraut a day . . .

The chemical structure of D-phenyllactic.

Savory sauerkraut, a traditional fermented cabbage dish, is not new, but in 2019, Claudia Stäubert’s group at Leipzig University found out what happened to students when they ate a large portion of the slightly sour stuff (PLOS Genet. 2019, DOI: 10.1371/journal.pgen.1008145).

A bowl of sauerkraut with the structure of D-phenyllactic acid.
Credit: C&EN/Shutterstock
D-phenyllactic acid, a molecule produced by sauerkraut bacteria, can affect people's immune systems.

By taking blood samples from the students after the meal, the researchers found that a metabolite, D-phenyllactic acid, produced by the bacteria that ferment the cabbage can activate the immune system. This is the first sign that sauerkraut might have a health role beyond nutrition. Bioinformatic analyses suggest that the receptor that D-phenyllactic acid binds to entered the ape genome around the same time that the enzyme that helps us metabolize alcohol, another product of fermentation, entered.

Millions of years ago, experts say, our ancestors started to eat fermented foods, and their bodies adapted to the new diet in ways that are still useful today.


A bug’s white

A close-up of a beetle with bright-white scales.
Credit: Andrew Parnell
The scales of the Cyphochilus beetle are inspiring next-generation white paints.

Cyphochilus beetle scales inspired a new white pigment this year. People usually use titanium dioxide nanoparticles to produce white paints, but Cyphochilus relies on nanostructuring to make its scales one of the brightest whites in nature. The beetle’s method for producing its scales is also more energy efficient than the one humans use to manufacture titanium dioxide. So Stephanie Burg, a PhD student at the University of Sheffield, looked at the beetle scales for inspiration for a new, environmentally friendly white pigment.

Burg mapped the structures of the little bug’s scales using 3-D X-ray nanotomography and then produced films from cellulose acetate that mimicked them. The result was an even brighter white than the beetle’s shade (Commun. Chem. 2019, DOI: 10.1038/s42004-019-0202-8). Now Burg is looking for an industrial partner to scale up her new idea.


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