The New York Times (EUA) online

How Do You Make a Less Toxic Blue Dye? Start With Red Beets

Publicado em 03 abril 2020

Por Joanna Klein | The New York Times


Usually these root vegetables cause pink stains, but with a little bit of chemistry, Brazilian researchers found they could produce another hue.

Blue is the color of clear skies and open water. It conjures calm. But it’s not easy being blue. It’s not the easiest color to make, either.

You can make a nice blue by mixing certain minerals with elements like mercury or lead. But they are toxic. Other methods of producing blue dyes can also be harmful to humans and the environment.

What if there was another way to make things blue, using something that is usually red? That’s what an organic chemist in Brazil tried.

“I like to think I’m kind of a molecular psychiatrist,” said Erick Bastos, who studies the chemistry of natural pigments at Universidade de São Paulo. “I check the structure of a molecule, and I try to imagine what kind of modification I can do in order to make the molecule obey me. It doesn’t always happen. It’s very difficult.”

By extracting a pigment from beets and tweaking its molecular pattern, Dr. Bastos transformed the pigment’s bashful blush to a brilliant blue. He calls it BeetBlue, and so far it appears to be nontoxic. The chemical reaction he and his colleagues demonstrated Friday in Science Advances brings us a natural blue, unpatented and free for all to modify.

Dr. Bastos became interested in making blue from beets because he had been working with betalains, rare pigments found in beet roots, dragon fruit and the fly agaric fungus (a typical red and white magic mushroom). Just a tiny amount of beetroot juice can render a lot of dye. It was natural and efficient.

He began with beets harvested from a farm near his lab.

“I’d get a truck with zillions of kilograms of beets and my students would want to kill me,” Dr. Bastos said.

It ended up being more practical to simply create his own betalains. He mixed these pigments with a couple ingredients, and a chemical reaction occurred, altering how atoms bound together to form the pigment molecules. Within seconds, the color transformed from red, to yellow, then green and blue.

Some of the most important advances in science — like the notion that individual neurons exist and communicate — came with the help of natural dyes, like silver golgi stain and green fluorescent protein. Inspired by the scientific heroes who discovered these, Dr. Bastos had originally intended to use BeetBlue for biomedical imaging.

But it didn’t work.

“I’m in the business of putting things inside the cell,” he said. “But BeetBlue is not good at doing this.”

He asked Barbara Freitas-Dörr, a graduate student he works with, to try using the dye for something else.

Much to his surprise, she returned after five minutes holding a tube of blue. After further processing, the pigment was scentless and felt like powdered sugar. It successfully dyed maltodextrin, a starchy food preservative, as well as yogurt, silk, cotton and samples of human hair.

And when tested on human liver cells, retinal cells and developing zebrafish, BeetBlue passed all tests for toxicity. These results suggest BeetBlue is safe, although Dr. Bastos stressed that “hyping it can be dangerous.” More tests are needed to know if it is truly safe and whether it will last in the wash.

For now, Dr. Bastos likes the romantic notion that everyone can take their shot at making their own BeetBlue

“I want people to use it, and play with it and make it better,” he said.