PHOTOSENSITIZERS IN ORGANIZED MEDIA: SINGLET OXYGEN PRODUCTION AND SPECTRAL PROPERTIES

Abstract— Measurement of singlet oxygen production by porphyrin-type photosensitizers in simple buffer solutions show that TPPS is more efficient than PII (Photofrin II) or than hematoporphyrin. This behavior was observed using three independent analytical detection methods for ¹O₂: RNO bleaching, tryptophan degradation, and oxygen consumption. Similar results were obtained when irradiating with a classical light source or with a pulsed dye laser. Addition of EPC liposomes to the buffer solution caused a decrease of efficiency for TPPS and an increase for PII. Addition of BSA shows the same relative pattern: a small increase of efficiency for TPPS and a tenfold increase for PII. These changes can be ascribed to specific interactions between the sensitizer molecules and the organized medium. Since changes in the fluorescence properties are also due to interactions with the medium, we monitored the emission of the sensitizers as a function of the environment. The fluorescence peak positions (at 648, 705 nm for TPPS and at 615, 677 nm for PII) were all red shifted. The intensities show an increase, particularly for PII in liposomes, due to a marked change in the microviscosity.