Photophysical properties and efficiency of singlet oxygen formation by a pH-sensitive sensitizer based on meso-tetrakis(4-N-methylpyridyl)porphyrin and hydroxyapatite nanoparticles

Abstract

The photophysical properties and efficiency of photosensitized singlet oxygen formation by meso-tetrakis(4- N-methylpyridyl)porphyrin in a complex with hydroxyapatite nanoparticles were studied. At least three types of complexes characterized by different access of oxygen to porphyrin molecules were shown to form on the surface of the hydroxyapatite nanoparticles. Rotation of the pyridyl substituents of porphyrin in the complex with hydroxyapatite nanoparticles was found to be significantly hindered, while porphyrin molecules on the surface of the nanoparticles were in a less polar environment than in water. The quantum yield of photosensitized singlet oxygen formation was observed to decrease by at least nine times for porphyrin in the complex with hydroxyapatite nanoparticles. Porphyrin was released from hydroxyapatite nanoparticles and the efficiency of singlet oxygen formation increased although it did not reach the values characteristic for free porphyrin if the pH decreased to less than 5.0 (pH < 5.0).