Chlorophylls B formulated in nanostructured colloidal solutions: Interaction, spectroscopic, and photophysical studies

Abstract

Chlorophylls (Chls) are natural pigments essential to photosynthesis that have been shown to act as photosensitizers for Photodynamic Therapy (PDT). Many studies have used Chls A and its colloidal formulations in the PDT field but little is known about the potential of Chls B for this application. Here we have detailed the interaction, spectroscopic, and photophysical properties of Chlorophyll b (Mg-Chl b), Pheophytin b (Pheo b), and its formulations with nonionic surfactants aiming photodynamic applications. Both pigments were formulated in some suitably nanostructured drug delivery systems based on aqueous solutions of Pluronics triblock copolymers and Tweens surfactants. High binding constants have evidenced that Chls B interact strongly with these micelles, and the results are correlated with logP, zeta potential, and hydrodynamic diameter. Spectroscopic studies showed high molar absorption coefficients in the therapeutic window (600–800 nm), significant fluorescence quantum yields, and solubilization of Chls B as monomers, especially for Pluronics systems. Pheo b is completely photostable in all investigated micellar systems, whereas Mg-Chl b is photobleached with a rate constant correlated with the interaction and relative location in these micelles. High singlet oxygen quantum yields identify these chlorophylls B as possible Type II photosensitizers for PDT. Mg-Chl b in particular is almost twice as effective as Mg-Chl a, which makes it one of the most potent generators of singlet oxygen in nature.