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The synthesis of zinc tetranitrophthalocyanine ( T 4 NO 2 ZnPc ) was carried out and two structural isomers ( C 2v and C s) were separated by column chromatography and characterized by 400 MHz proton nuclear resonance spectroscopy and absorption spectroscopy. The photophysical and photobiological parameters for isomers C 2v and C s were determined in solution and in the presence of macrophage cell culture (J774A). The results obtained clearly indicated that the photophysical, photochemical and photobiological properties of the two isomers were different and each isomer showed a different biological behavior.

The photogeneration of nitric oxide (NO) using laser flash photolysis was investigated for S-nitroso-glutathione (GSNO) and S-nitroso-Nacetylcysteine (NacySNO) at pH 6.4 (PBS/HCl) and 7.4 (PBS). Irradiation of S-nitrosothiol with light (l = 355 nm followed by absorption spectroscopy) resulted in the homolytic decomposition of NacySNO and GSNO to generate radicals (GS · and NacyS · ) and NO. The release of NO from donor compounds measured with an ISONometer apparatus was larger at pH 7.4 than pH 6.4. NacySNO was also incorporated into dipalmitoyl-phosphatidylcholine liposomes in the presence and absence of zinc phthalocyanine (ZnPC), a wellknown photosensitizer useful for photodynamic therapy. Liposomes are usually used as carriers for hydrophobic compounds such as ZnPC. Inclusion of ZnPC resulted in a decrease in NO liberation in liposomal medium. However, there was a synergistic action of both photosensitizers and S-nitrosothiols resulting in the formation of other reactive species such as peroxynitrite, which is a potent oxidizing agent. These data show that NO release depends on pH and the medium, as well as on the laser energy applied to the system. Changes in the absorption spectrum were monitored as a function of light exposure. Correspondence