INTERACTIONS OF DICARBOXYLIC PORPHYRINS WITH MEMBRANES IN RELATION TOTHEIR IONIZATION STATE

The interactions of dicarboxylic porphyrins with membrane systems are discussed with particular emphasis on the effect of the charge of the porphyrin and the nature of the side-chains. The incorporation of hema toporphyrin or related dicarboxylic porphyrins within small unilamella r vesicles as membrane models is favored by a decrease of the pH in th e range of physiological pH values. This effect might play an importan t role in the retention of porphyrins by tumors, which are more acidic than normal tissues. Kinetics studies also show that the partition of the porphyrin between the lipidic bilayer and the aqueous phase is go verned by its release rate rather than by its incorporation rate.