Aggregation study of Triarylmethane dyes

Córdoba

Congreso; 3rd International Meeting on Pharmaceutical Sciences; 2014

Photodynamic therapy (PDT) is a non-invasive medical technology that involves three key components: photosensitizer (PS), light and tissue oxygen to generate reactive oxygen species, which cause cells death. Numerous studies in bibliography report that many PS tend to aggregate in aqueous solution. Due to these molecular assemblies present lower photochemical reactivity than the respective monomer, self-aggregation of New Fuchsin (NF) and its di-iodinated derivative (NFI2) were evaluated by UV-Visible Spectroscopy.Dye concentration effect in N,N-Dimethylformamide (DMF), DMF: water mixtures and aqueous solution were compared. UV-Visible spectra obtained for NFI2 in DMF showed a unique band with a maximum absorption at 460 nm. When water proportion was increased, a new band at 574 nm was observed and the dye presented maxima absorption at 558 nm and 525 nm in pure aqueous media. Moreover, absorption spectra of NF in DMF showed a single band with a maximum absorbance at 558 nm, while in aqueous solution an increase in absorbance of shoulder at 495 nm was observed along with increasing dye concentration.Due to DMF is a monomerizing solvent, the unique absorption band observed for NFI2 in this medium could be assigned to monomeric form. When water was added, this species began to form J-aggregates (574 nm). Moreover, high order assemblies were observed in aqueous solution (558 nm and 525 nm). Comparing these results with those obtained for NF, we can conclude that, under the experimental conditions, the monomeric species of NF was not observed.In conclusion, the substitution by iodine in the structure of NF, destabilized the J-aggregate, which allowed identify the monomeric form in DMF as well as to larger aggregates in aqueous solution. Due to NFI2 presented lower tendency to J-Aggregates formation than NF, it could present higher photochemical reactivity than its precursor and could be good candidate for use in PDT.