Photophysical properties and interaction studies of Rose Bengal derivatives with biomimetic systems based in micellar aqueous solutions

Abstract

Xanthene dyes are compounds extensively used in Photodynamic Therapy against infection caused by microorganisms, cancer and other diseases. In this study, structural changes in Rose Bengal (RBB) xanthene photosensitizer (PS) were performed in order to improve its interaction with biological substrates. In this way, hydrophobic RBB ester derivatives were obtained through insertion of a hydrocarbon chains containing 1, 4 and 10 carbons. The spectroscopic and photophysical properties of these compounds in homogeneous medium (water at physiological pH) and micro-heterogeneous micellar systems formed by sodium dodecyl sulfate (SDS), cetyl trimethylammonium bromide (CTAB) and Pluronic™ P-123 copolymeric surfactant were evaluated. The interaction between the PS and these micelles showed that association and location are significantly dependent on PS and micelle charges, length of the inserted hydrocarbon tail (hydrophobic effects) and the micellar structure. The binding constants (Kb) for the xanthenes in SDS, P-123 and CTAB micelles follow the same trend of the partition coefficients, which reveal the influence of the hydrophobic effects on PS/micelle interaction. Resonance Light Scattering (RLS) and fluorescence anisotropy studies showed the formation of pre-micellar aggregates of PS combined with CTA+ which justifies the high Kb values in this system. Comparative analyses of Stern-Volmer constant (KSV) confirm the pKa results showing that location of each PS into the micelles depends on both, its hydrophobicity and charge. Finally, singlet oxygen quantum yield (ΦΔ1O2) of the ester derivatives presented values from 0.83 to 0.89 such shows that they exhibit high potential to be applied in future photodynamic treatments.