Interaction of Porphyrins with Micelles

Raymond Wu
San Francisco State University

Due to their ability to localize in membranes or membranous organelles of cells of diseased tissues and their fluorescence properties, porphyrinic pigments are investigated with great interest in photodynamic therapy (PDT) of cancers, age-related macular degeneration (AMD), and other diseases. Since little is known why and how these pigments localize in membranes or membranous structures, it is the objective of this research to determine the characteristics that porphyrins must have to localize with great affinity in membranes and to investigate their membrane affinities and localization properties. To this end two porphyrins bearing two hydroxy- and two fluorophenyl-substituents were synthesized. After through purification, one of these porphyrins, namely the so-called cis-substituted porphyrin, 5,10-(4-difluorophenyl)-15,20-(4-dihydroxyphenyl)porphyrin was allowed to diffuse into cationic, anionic, and non-ionic micelles. The micelles were formed by the surfactants dodecyltrimethylammonium bromide, dodecylbenzenesulfonate, and polyethylene(20)sorbitan monolaureate. Characteristic shifts observed in the 1H NMR spectra indicate that the porphyrin diffused only into cationic and non-ionic micelles under all pH conditions, but not into anionic micelles. The membrane incorporation efficiency of the porphyrin was optimal when the headgroups of the surfactants are non-ionic and when the the pH of the environment was basic. These results indicate that electrostatic interactions and pH are important characteristics for embedding porphyrins into micelles and important considerations when designing clinically useful agents for PDT.