The deactivation pathways of the excited-states of the mycosporine-like amino acids shinorine and porphyra-334 in aqueous solution

Abstract

In vitro studies on the structurally related mycosporine-like amino acids (MAAs) porphyra-334 and shinorine in aqueous solutions were carried out aiming at their full photochemical and photophysical characterization and expanding the evidence on the assigned UV-photoprotective role of the molecules in vivo. The experiments on shinorine confirmed a high photostability and a poor fluorescence quantum yield, in concordance with previous results on porphyra-334. The estimation of triplet production quantum yields for both MAAs was achieved by laser-flash photolysis measurements. In particular, photosensitization experiments on porphyra-334 support the participation of the triplet state in the photodecomposition mechanism yielding a more precise value of [capital Phi](T). As well, photoacoustic calorimetry experiments allowed the first direct quantification of the nonradiative relaxation pathways of the excited MAAs in solution, corroborating that the vast majority (ca. 97%) of the absorbed energy is promptly delivered to the surroundings as heat, consistently with the low photodecomposition and emission yields observed.

Characterization of the chemical diversity of glycosylated mycosporine-like amino acids in the terrestrial cyanobacterium Nostoc commune

“…In cyanobacteria, MAAs protect the cells against solar radiation [28,29]. The energy absorbed by MAAs is promptly dispersed into the surroundings as heat [30,31]. Thus, MAAs do not function as accessory pigments in photosynthesis [23].…”

The extraordinary longevity of kleptoplasts derived from the Ross Sea haptophyte Phaeocystis antarctica within dinoflagellate host cells relates to the diminished role of the oxygen-evolving Photosystem II and to supplementary light harvesting by mycosporine-like amino acid/s

“…[36]) only shinorine has been reported to fluoresce; ref. [37,38]). This, perhaps, relates to shinorine being a cyclohexenimine derivative, while the other two MAAs are cyclohexenone derivatives.…”

Photoprotection mechanisms against ultraviolet radiation in Heterocapsa sp. (Dinophyceae) are influenced by nitrogen availability: Mycosporine‐like amino acids vs. xanthophyll cycle

“…Interestingly, it has been shown that these mechanisms are inversely coupled in Heterocapsa sp. Under N-replete conditions, UVR stimulated MAA accumulation, with the consequent energy dissipation as heat (Conde et al 2004). However, under N limitation, MAA content decreased but the deepoxidation degree of the xanthophyll cycle pigments increased.…”

“…The protection from harmful UVR by MAAs is because of their UV-screen properties (Conde et al 2004; Korbee et al 2006) and their antioxidant scavenging capacity (Dunlap and Yamamoto 1995;de la Coba et al 2009). A correlation between MAAs and in situ irradiance levels has been noticed in many locations and in a wide variety of organisms (Korbee et al 2006).…”