Unravelling the Photoprotective Mechanisms of Nature-Inspired Ultraviolet Filters Using Ultrafast Spectroscopy

Abstract

There are several drawbacks with the current commercially available ultraviolet (UV) filters used in sunscreen formulations, namely deleterious human and ecotoxic effects. As a result of the drawbacks, a current research interest is in identifying and designing new UV filters. One approach that has been explored in recent years is to use nature as inspiration, which is the focus of this review. Both plants and microorganisms have adapted to synthesize their own photoprotective molecules to guard their DNA from potentially harmful UV radiation. The relaxation mechanism of a molecule after it has been photoexcited can be unravelled by several techniques, the ones of most interest for this review being ultrafast spectroscopy and computational methods. Within the literature, both techniques have been implemented on plant-, and microbial-inspired UV filters to better understand their photoprotective roles in nature. This review aims to explore these findings for both families of nature-inspired UV filters in the hope of guiding the future design of sunscreens.

A Perspective on Femtosecond Pump–Probe Spectroscopy in the Development of Future Sunscreens

“… Schematic of a typical transient electronic absorption spectroscopy (TEAS) setup. Reprinted with permission from ref ( 38 ). Copyright 2020 MDPI.…”

UV Filters: Challenges and Prospects

“…In fact, most of UV filters are inspired in natural products, specifically of botanical, animal, or mineral origin [ 5 ]. In 1928, benzyl salicylate was discovery for its photoprotective action against UVB radiation, but it was only commercialised in 1935 in the first sunscreen “Ambre Solaire” [ 6 , 7 ]. Later, almost 50 years, avobenzone and its derivatives appeared as the first UV filters that ensure protection against UVA radiation [ 8 ].…”

Unravelling the Photoprotection Properties of Garden Cress Sprout Extract

“…Despite the many sunscreen formulations currently available, certain setbacks such as the potential toxicity to humans and the environment, as well as photo-instability, have resulted in the banning of some UV filters [7][8][9][10]. To this effect, sunscreen scientists have continued to search for safe and efficient UV filters, seeking inspiration from natural sources, including plants and microorganisms [11]. For example, in plants, sinapoyl malate (SM, see Figure 1A), found in the upper layer of Brassicaceous plants such as thale cress (Arabidopsis thaliana), has been reported to be the photoprotective agent [12,13].…”

“…For example, in plants, sinapoyl malate (SM, see Figure 1A), found in the upper layer of Brassicaceous plants such as thale cress (Arabidopsis thaliana), has been reported to be the photoprotective agent [12,13]. In order to elucidate the photoprotection mechanism, the photodynamics of SM and its derivatives have also been studied [11,[14][15][16][17][18][19]. Briefly, these studies have shown that following UV absorption, SM and its derivatives undergo an efficient and ultrafast energy relaxation mechanism, predominantly trans-to-cis photoisomerisation, which accounts for their longterm photostability and photoprotective nature.…”