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Potential long-lasting UV blocker for sunscreens identified

Photo by: Dr Michael Horbury, University of Warwick

A molecule that protects plants from damage from ultraviolet (UV) light could form the basis of new, longer-lasting sunscreen products for humans due to its ability to absorb the radiation and effectively convert it to heat without breaking down.

The research was conducted by chemists at the University of Warwick, Coventry, U.K., in collaboration with colleagues in France and Spain.

In a paper published in Nature Communications (Oct. 18; 10(1):4748), investigators detailed how they investigated a molecule—diethyl sinapate—a close mimic to a molecule commonly found in the leaves of plants, which protects them from overexposure to UV light.

Researchers first exposed the molecule to a number of different solvents to determine whether that had any impact on its (principally) light absorbing behaviour. They then deposited a sample of the molecule on an industry standard human skin mimic—VITRO-CORNEUM—where it was irradiated with different wavelengths of UV light. They then used ultrafast spectroscopy to take images of the molecule at extremely high speeds, to observe what happens to the light’s energy very shortly after it is absorbed—within trillionths of a second. Other techniques were also used to establish longer term—over many hours—properties of diethyl sinapate, such as endocrine disruption activity and antioxidant potential.

Senior co-author Professor Vasilios Stavros from the University of Warwick, Department of Chemistry, said in a press release: “A really good sunscreen absorbs light and converts it to harmless heat. A bad sunscreen is one that absorbs light and then, for example, breaks down potentially inducing other chemistry that you do not want. Diethyl sinapate generates lots of heat, and that is really crucial.”

When exposed to UV light, the molecule absorbs it and goes into an excited state but that energy then has to be disposed of somehow. The team of researchers observed that it does a kind of molecular ‘dance’ a mere 10 picoseconds long, folding and twisting. That causes it to come back to its original ground state and convert that energy into vibrational energy, or heat.

It is this ‘dance’ that gives the molecule its long-lasting qualities. When the scientists bombarded the molecule with UVA light they found that it degraded only 3% over two hours, compared to the industry requirement of 30% (for UV blocking ingredients in sunscreen).

Dr Michael Horbury, who was a Postgraduate Research Fellow at The University Warwick when he undertook this research, and is now at the University of Leeds, said in the release: “We have shown that by studying the molecular dance on such a short time-scale, the information that you gain can have tremendous repercussions on how you design future sunscreens. Future research would involve testing diethyl sinapate in human skin, and combining it with other ingredients commonly found in sunscreen products.

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