SINGLET OXYGEN GENERATION BY PORPHYRINS AND THE KINETICS OF 9,10-DIMETHYLANTHRACENE PHOTOSENSITIZATION IN LIPOSOMES

Two new sensitizers are introduced for a potential use in photodynamic therapy: Zn2+- and MG2+-tetrabenzoporphyrin (ZnTBP and MgTBP). A comp arative study of the quantum yields of singlet oxygen generation (PHI( DELTA)) of hematoporphyrin derivative (HpD), Photofrin II (PF-II), Zn2 +-phthalocyanine tetrahydroxyl [ZnPC(OH)4] and the newly introduced se nsitizers ZnTBP and MgTBP in liposomes, as well as the kinetics of a p hotochemical reaction sensitized by them, was made by employing the fl uorescent membrane probe 9,10-dimethylanthracene (DMA). We followed th e photosensitization of DMA in real time by monitoring its fluorescenc e decrease at 457 nm and found that DMA's photosensitization is oxygen mediated. The kinetic traces of the photosensitization reactions were fitted to an analytical function, and the PHI(DELTA) values were eval uated. At 10 muM sensitizer in an aqueous suspension of 2 mg/mL egg ph osphatidylcholine (EPC), HpD was found to have the largest value of PH I(DELTA) (0.215), followed by PF-II (0.191), ZnTBP (0.023), MgTBP (0.0 19) and ZnPC(OH), (0.005). As a test of the method, PHI(DELTA) for met hylene blue in ethanol was measured and found to be 0.45 as compared t o 0.52 reported in the literature. Due to difference in the sensitizer s' absorbances at the laser's wavelength, the reaction photosensitized by ZnTBP was the fastest with a time constant of 6.7 min, followed by MgTBP (8.7), PF-II (11.9), HpD (1 7. 1) and ZnPC(OH)4 (31.2), all at equal sensitizers' concentrations and laser intensities. The binding c onstants of the sensitizers to EPC liposomes are also reported.