Laser Flash Photolysis Of Tetrapyrrole Compounds

ABSTRACTPhotodynamic therapy (PDT) is a new promising treatment modality with many advantages such as good treatment efficiency, minor side effects, simple conditions for treatment, et al.It needs undergo the following procedure. Firstly, A suitable photosensitizer for pathological tissues is chosen. Then, the photosensitizer is directed into the body, usually by the intravenous injection, and subdivided in the tissues of nidus. Finally, when the concentration ratio of photosensitizer between the target tissues and normal tissues reached a peak , the photosensitizer is irradiated with the matched laser and excited to the excited singlet-state (S) which can be converted to the excited triplet-state (T) by intersystem crossing. Then the excited tripet-state (T) directly damage the target tissue or indirectly damage the target tissue through the reactive oxygenic spices generated by reacting with O.According to those mentioned above, we know that choosing a right photosensitizer is crucial to the PDT.Most of the chlorophyl derivatives and tetraphenyl porphyrin derivatives have great photosensitivity, their prime cost is relativly cheap, and they are both tetrapyrrole compounds. So we decide to study the laser flash photolysis of these two tetrapyrrole compounds and expect to know the photosensitic property of tetrapyrrole compounds so as to search and choose the cyclic tetrapyrrole photosensitizer more exactly.Our major research is consisted with the followings:(1) Mg-purpurin-18 was synthesized from Chl a.(2) Tetra (meso-chlorophenyl) porphyrin was synthesized.(3) The laser flash photolysis of Mg-purpurin-18, tetra (meso-chlorophe nyl) porphyrin and 2, 7, 12, 18-tetramethyl-3, 8-bis (1-iso-butoxyl) eth-yl-13, 17-bis[3-bis (2-chloroethyl) amino]-propylporphy rin(porphyrin-nitrogen mustards) were studied and the products of photoactivation were determined.(4) The decay mechanisms and decay coefficient under the O saturated condition and the N saturated condition were determined.From the experiment we found that after irradiated by 355nm laser, tetra-(meso-chlorophenyl)-porphyrin was photoionazed but Mg-purpurin-18 and porphyrin nitrogen mustards produced the excited triplet-state. By comparing the structures of the three compounds, we had an opinion that the photoionazation of tetra-(meso-chlorophenyl)-porphyrin was caused by the strong electron donating of meso-chlorophenyl.The excited triplet-state can react with O which showes that Mg-purpurin-18 and porphyrin nitrogen mustards are able to become new photodynamic drugs.According to the mechanism of UV spectrum and the structures of the three compounds, the occurrence of two extra absorption bands of Mg-purpurin-18 was due to two extra conjugated carbonyl groups. The two extra absorption bands suggest that Mg-purpurin-18 will have more suitable light sources in PDT.In short, we studied the photolysis property of three tetrapyrrole compounds. By comparing their structures and photosensitive properties, we provided some information for searching and choosing suitable tetrapyrrole photosensitizers.