Interaction of eosin and its ester derivatives with aqueous biomimetic micelles: Evaluation of photodynamic potentialities

In this paper, the physicochemical and photophysical properties of xanthene dyes interacting with micelles were evaluated. Xanthenes are potential photosensitizers for photodynamic therapy. The dyes were eosin Y and its ester derivatives with methyl, butyl and decyl alkyl groups. eous media at physiological pH eosin is present as dianionic protolytic form while its esters are monoanionic. Analysis of the water/octanol partition coefficient showed that the eosin is the most hydrophilic compound and the hydrophobicity increases as the alkyl chain of the ester increases: eosin < methyl ester < butyl ester < decyl ester. Computational calculations of the dipole moments, molecular volume, charge distribution, solvation energy and molecular orbital performed by the B3LYP/DGDZVP method and IEFPCM solvent model, allowed to justify the electronic absorption properties and its dependence with the dye environment. In order to mimic the interaction of these compounds with membranes, it was used micelles of sodium dodecyl sulfate (SDS), cetyl trimethylammonium bromide (CTAB) and polymeric micelles (Pluronics®) of P-123 and F-127. The binding constant between the xanthenes and micelles increased with the hydrophobicity of the dye in all evaluated systems. Furthermore, we observed the formation of pre-micellar aggregates when using cationic CTAB micelles due to electrostatic attraction. The iodide fluorescence quenching showed that the more hydrophobic photosensitizer were located deeply within the micelles. The fluorescence quantum yield values increased in the presence of surfactants, indicating protection against non-radiative deactivation. The dyes singlet oxygen quantum yield values suffered a small decrease when formulated in micelles, however they are still suitable for photodynamic applications. The results show that eosin and its ester derivatives have favorable characteristics for use in photodynamic therapy, particularly formulated in biocompatible polymeric surfactants such as Pluronics®.