Reinvestigating the Photoprotection Properties of a Mycosporine Amino Acid Motif

Abstract

With the growing concern regarding commercially available ultraviolet (UV) filters damaging the environment, there is an urgent need to discover new UV filters. A family of molecules called mycosporines and mycosporine-like amino acids (referred to as MAAs collectively) are synthesized by cyanobacteria, fungi and algae and act as the natural UV filters for these organisms. Mycosporines are formed of a cyclohexenone core structure while mycosporine-like amino acids are formed of a cyclohexenimine core structure. To better understand the photoprotection properties of MAAs, we implement a bottom-up approach by first studying a simple analog of an MAA, 3-aminocyclohex-2-en-1-one (ACyO). Previous experimental studies on ACyO using transient electronic absorption spectroscopy (TEAS) suggest that upon photoexcitation, ACyO becomes trapped in the minimum of an S 1 state, which persists for extended time delays (>2.5 ns). However, these studies were unable to establish the extent of electronic ground state recovery of ACyO within 2.5 ns due to experimental constraints. In the present studies, we have implemented transient vibrational absorption spectroscopy (as well as complementary TEAS) with Fourier transform infrared spectroscopy and density functional theory to establish the extent of electronic ground state recovery of ACyO within this time window. We show that by 1.8 ns, there is >75% electronic ground state recovery of ACyO, with the remaining percentage likely persisting in the electronic excited state. Long-term irradiation studies on ACyO have shown that a small percentage degrades after 2 h of irradiation, plausibly due to some of the aforementioned trapped ACyO going on to form a photoproduct. Collectively, these studies imply that a base building block of MAAs already displays characteristics of an effective UV filter.

Towards developing novel and sustainable molecular light-to-heat converters

“…The TVAS setup and experimental technique employed in this work have also been reported in detail previously 32,58 and, again, only information specific to the current experiments is reported. TVAS measurements of CBA and CDBA were undertaken in DMSO at 30 mM concentration, using the same sample delivery system as for the TEAS studies, but with a 150 µm thick spacer (to achieve a change in optical density ∆OD of 0.002) and a maximum pump-probe delay of 2.5 ns.…”

Exploring the Blueprint of Photoprotection in Mycosporine-like Amino Acids

“…While the above findings imply nonradiative decay to be the dominant relaxation mechanism, tracking this UV-to-heat energy transfer process in real time has remained elusive. Ultrafast spectroscopy can be used to track, and understand in unrivalled detail, energy flow; indeed, such studies have revealed energy transfer processes in MAA motifs − but not for the MAAs themselves. More broadly, an understanding of molecular photon-to-heat conversion impacts environmental, medicinal, and cosmeceutical industries to name a few.…”

Molecular Design Learned from the Natural Product Porphyra-334: Molecular Generation via Chemical Variational Autoencoder versus Database Mining via Similarity Search, A Comparative Study

“…A variety of UV-absorbing molecules, termed mycosporine-like amino acids (MAAs), have been reviewed by several researchers. − ,− The MAAs from a marine organism are imine derivatives of mycosporines, as shown in Figure a. The MAA motif contain an amino-cyclohexen imine ring linked to an amino acid, an amino alcohol, or an amino group, which absorbs UV light from 320 to 362 nm and shows photoprotective and antioxidant functions.…”