Chemical equilibria of Eosin Y and its synthetic ester derivatives in non-ionic and ionic micellar environments

Eosin (EOS) and its synthetic ester derivatives have adequate properties to be employed as histologicalmarkers for and as drugs for photodynamic therapy. However, they present a very complex protolytic and tautomeric equilibrium that reflects on their photophysical properties. Hence their biomedical applications are strongly affected by the medium's pH, charge and hydrophobicity. In this study, we evaluated the effects of two neutral (Pluronic (R) F-127 and P-123) and two ionic (anionic SDS and cationic CTAB) surfactant micelles as a simplemembranemodel on the protolytic/tautomeric equilibrium of EOS and its ester derivative dyes. Multivariate analysis based on Q-Imbrie's factor and the K-matrix method on the electronic absorption spectroscopy data in different pHconditions allowed for the understanding of the complex protolytic/tautomeric equilibrium, and the influence of medium microenvironment on the EOS dyes at each pH. Our results demonstrated that, when close to physiological pH (similar to 7.4), and electrostatic attraction towards cationic surfaces favor dyes locating close to themicelle's (biomembrane model) interface, where their biomedical applications are favored. Therefore, the analysis in different environments shows that the interactions of EOS and its derivativeswith biomembranes can bemodulated based on the hydrophobicity of the xanthene derivative and the cell membrane charge. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study evaluated the effects of surfactant micelles on the protolytic/tautomeric equilibrium of Eosin and its ester derivative dyes, showing that electrostatic attraction towards cationic surfaces favored the dyes locating close to the micelle interface near physiological pH, enhancing their biomedical applications.