Fluorescence Analysis of Meta-Tetra(Hydroxyphenyl)Chlorine Complexation with Monomeric and Polymeric Cyclodextrins

Spectral methods have been developed for analyzing the equilibrium and kinetics of the complexation process of the known photosensitizer, meta-tetrakis(hydroxyphenyl)chlorine (mTHPC), with monomeric and polymeric derivatives of β-cyclodextrin (β-CD). The study of the binding isotherms showed that mTHPC has a higher affinity for the polymeric derivatives of β-CD studied, namely, carboxymethyl-β-cyclodextrin polymer (CM-β-CDPD) and β-cyclodextrin polymer (β-CDPD), than for monomeric methyl-β-cyclodextrin (M-β-CDMD). Profiles for the change in the relative content of mTHPC inclusion complexes with β-CDs in solution with and without the presence of lipid vesicles were obtained and the dissociation constants of the photosensitizer (PS) molecules were calculated from the content of the inclusion complexes with cyclodextrins. The dissociation of mTHPC from the inclusion complexes with M-β-CDMD takes 1–2 min, while this process takes more than one hour with polymeric CDs, (CM-β-CDPD and β-CDPD). These findings suggest that the complexation of the title chlorine with polymeric and monomeric cyclodextrins may play an essential role in the delivery of photosensitizer to cellular/tissue structures.