Photophysicochemical characterization of mycosporine-like amino acids in micellar solutions

Abstract

The properties and photochemical and photophysical behavior of the mycosporine-like amino acids (MAAs) shinorine and porphyra-334 were experimentally evaluated in solutions of direct ionic micelles as simple biomimicking environments. The preferential partition of the natural molecules in the aqueous phase of sodium dodecyl sulfate (SDS) or cetyltrimethylammonium chloride (CTAC) micellar systems is confirmed. Although the proton dissociation of the carboxylic groups in the MAAs is slightly inhibited in CTAC solutions, the molecules are predicted to be in the form of zwitterions in all the explored media around physiological pH. The increase in the fluorescence quantum yield, emission lifetime and stationary anisotropy in the presence of CTAC micelles suggest electrostatic attractions of the MAAs with the surface of the cationic micelles. Consistently, the triplet-triplet absorption spectra in CTAC solutions reveal the typical environmental features of the micellar interface, while in the presence of SDS they are similar to those determined in neat water. Finally, the photostability of the MAAs increases in the micellar systems, more noticeably in the case of CTAC. It is concluded that the ability of the two MAAs to act as UV screens is susceptible to the influence of electrostatic interactions with organized microheterogeneous environments.

Photochemistry and Photophysics of Shinorine Dimethyl Ester

“…Indeed, the parameters in Table 1 account for relative decreases in the photodecomposition quantum yields by factors of two in water and of six in SDS solution. Thus, the effects in micellar media for SDME are in line with the results for shinorine and porphyra-334: the stronger coulombic attractions with the micellar surface, the better protection toward photodecomposition (18).…”

“…Electrostatic interactions have been already invoked to account for the micellar effects in the photophysics of the MAAs shinorine and porphyra‐334 in SDS and CTAC solutions . The results of that previous study support the preferential solubilization of the MAAs in the aqueous phase outside the direct micelles and, due to the zwitterionic character of the natural compounds under physiologic pH, the possibility of columbic interactions with the charged heads of the surfactants.…”

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

“…Recently, Orallo et al [ 136 , 137 ] have performed studies on the MAAs shinorine, porphyra-334 and shinorine dimethyl ester in micellar solutions to elucidate the photochemistry and photophysics in a closer-to-real sunscreen formulation environment. They found that the fluorescence quantum yield and lifetime were increased in micelle solutions compared to aqueous solutions; however, the main deactivation process remained via non-radiative decay.…”

“…The authors attributed both properties to the electrostatic interactions between MAAs and micelles which hinder molecular movements. Overall, Orallo et al [ 136 , 137 ] demonstrated that MAAs in micellar solutions which mimic a closer-to-real environment, with regards to sunscreen formulation, still perform as efficient UV filters which is promising for commercial applications. However, the electrostatic interactions which influence the decay mechanisms must be taken into account.…”

“…In terms of the future direction for nature-inspired UV filters, the work by Horbury et al [ 115 ] carried out on DES ( Section 2.1.3 ) and Orallo et al [ 136 , 137 ] carried out on MAAs ( Section 2.2.2 ) serve as pertinent examples of the need to study the photodynamics of potential UV filters in a closer-to-real environment. It is important that such work is continued across UV filter research in order to determine any differences between the photodynamics of the targeted molecule in solution and on a skin mimic.…”