Unravelling photoprotection in microbial natural products

Abstract

Mycosporine-like amino acids have long been known as a natural form of photoprotection for fungi and cyanobacteria. This review will highlight the key time-resolved experimental and theoretical techniques unravelling their photochemistry and photophysics, and directly link this to their use in commercial skin-care products, namely as sunscreen filters. Three case studies have been selected, each having aided advancement in this burgeoning field of research. We discuss these studies in the context of photoprotection and conclude by evaluating the necessary future steps towards translating the photochemistry and photophysics insight of these nature derived sunscreen filters to commercial application.

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

“…We begin the mycosporine discussion by reviewing work conducted by Losantos et al [ 89 ] and Woolley et al [ 85 ] on basic cyclohexenone structures, herein referred to as mycosporine motifs. Further details of these authors’ works can be found in the reviews by Holt and Stavros [ 55 ] and Woolley and Stavros [ 83 ]. As a result, only a brief review will be given here.…”

“…Their findings were that in both solvents, a persistent ESA was present at extended time delays, Δ t > 2.5 ns, and this was attributed to the trapped population of ACyO in the minimum of the S 1 PES [ 85 ]. As the TAS have been reviewed previously [ 55 , 83 ], no further details are given here. In addition to the TEAS experiments, Woolley et al [ 85 ] also conducted complementary CASSCF calculations on ACyO to calculate critical points along the S 1 PES.…”

“…As with the mycosporine discussion in Section 2.2.1 , this section of the review will begin with the MAA motif studies [ 85 , 89 ]. Only a brief overview is required as previous publications have reviewed these studies [ 55 , 83 ] (see Section 2.2.1 for more details). Losantos et al [ 89 ] studied several molecules with a cyclohexenimine core, molecules 4–8 given in Figure 14 , using the same CASPT2//CASSCF methodology [ 119 , 120 ] supra.…”

“…There have been a number of studies on the photochemistry and photophysics of MAAs and these will be explored in some detail in this review [ 66 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 ] (for more detailed reviews on the photochemistry and photophysics of MAAs, the reader is directed to reviews by Losantos et al [ 62 ] and Woolley and Stavros [ 83 ]). To date, there has been no published ultrafast spectroscopy measurements on natural MAAs.…”

“…Ultrafast pulse generation in a TEAS experimental setup is commonly achieved by a Ti:Sapphire oscillator together with regenerative amplification to generate a fundamental 800 nm femtosecond laser pulse with (typically) a pulse energy of a few mJ [ 83 , 95 ]. The laser system output is then split into two beams, allowing for the generation of the pump and probe pulses.…”