Long summer days are here, and that means more chances for exposure to the sun’s harmful ultraviolet rays. Melanin pigments that give our skin, hair, and eyes colour are our best natural defense; they absorb and dissipate UV light to protect our cells from damage. If we can figure out how they work, we could create compounds for a nature-inspired sunscreen.
But despite centuries of study, scientists still don’t understand their molecular structure. They are complex and too unstable to isolate and study down to an atomic level.
Indole-5,6-quinone (IQ) is an intermediate molecule that is a building block of eumelanin — the most common type of melanin found in skin. Researchers at McGill University, Ohio State University, and the University of Girona figured out a way to synthesize a stabilized version of IQ to study its structure. Their study was published in Nature Chemistry.
The stabilized IQ had several unexpected properties that give it improved function over previous attempts to make compounds that mimic eumelanin.
“When we made this molecule, we anticipated that it would be like all other quinones that had been previously studied and that it would absorb and then emit light,” said co-principal investigator Jean-Philip Lumb, associate professor of chemistry at McGill University, in a press release.
“But we found that this deceptively simple molecule does something extraordinary: it takes all of the energy that it absorbs from light and converts it into heat.”
That’s important because the conversion of light into another form of energy is exactly what sunscreens are meant to do. Today, that is achieved using minerals or chemicals.
The stabilized IQ works across a broad spectrum of light, covering ultraviolet and near-infrared wavelengths. It’s the smallest known molecule to do this. Instead of the billions of atoms found in melanin granules, it has only a few dozen. That makes it easier to synthesize and tailor for new applications.
It was a surprise finding that only a single building block was needed to achieve the properties they observed. Natural melanin has long chains of its building blocks, and it was assumed that interactions between blocks would be essential to function.
Because the team’s approach was to create a synthetic melanin, they know precisely where every atom is located. That knowledge helps them understand how properties emerge as a result of these atomic configurations.
Melanin still has more secrets to unlock, such as how it gets its brown colour (the stabilized IQ used in the study is a bright green!), but this work illuminates the structure behind its UV-blocking properties.