Abstract
It has been said that singlet oxygen (1O2) has an important role on killing tumor cells in the photodynamic therapy using laser and hematoporyphyrin (Hp) or hematoporphyrin derivative (HpD). To evaluate the effect of the rate equation of 1O2 during the photodynamic reaction, the lifetime of excited triplet state of Hp was determined using CCl4, C2 H5OH and water as the solvent. The rate equation of 1O2 was very low due to the short lifetime of excited triplet state of Hp. Those was 480ns in CCl4, 280ns in C2H5OH and unmeasurable in water. It was suggested that the lifetime of excited triplet state of Hp was based on dye triplet-triplet absorption induced by Nd-YAG or N2 dye laser, and the difference in the lifetime was due to the radiationless energy transfer rate of the solvent by molecular vibration.
Additionally, the optical density of Hp was determined in various concentration under O2 bubbling using the solvents described above. The increased absorption was found at 502nm under O2 bubbling, and the increased optical density was correlated with the O2 and Hp concentrations. The energy level in wave length of 502nm was thought to be the sum of the energy levels of O2 and of excited triplet state of Hp. These results suggest that the increased absorption was produced by “cooperative absorption” of Hp-O2 complex.
Thus the elevation of the rate equation of 1O2 by the irradiation of a specific wave length of laser under high concentration of O2 circumstance will improve the efficiency of the photodynamic therapy on cancer.
