Abstract
Two zinc(II) phthalocyanines bearing either four methoxy (ZnPc 3) or trifluoromethylbenzyloxy (ZnPc 4) substituents have been synthesized by a two-step procedure starting from 4-nitrophthalonitrile. Absorption and fluorescence spectroscopic studies were analyzed in different media. These compounds are essentially non-aggregated in the organic solvent. Fluorescence quantum yields ( ϕ F) of 0.26 for ZnPc 3 and 0.25 for ZnPc 4 were calculated in tetrahydrofuran (THF). The photodynamic activity of these compounds was compared in both THF containing photooxidizable substrates and in vitro on Hep-2 human larynx-carcinoma cell line. The production of singlet molecular oxygen, O 2( 1Δ g), was determined using 9,10-dimethylanthracene yielding values of ∼0.56 for both sensitizers. Under these conditions, the addition of β-carotene (Car) suppresses the O 2( 1Δ g)-mediated photooxidation. In biological medium, no dark cytotoxicity was found for cells incubated with 0.1 μM of phthalocyanines 3 and 4 for 24 h. However, under similar conditions 0.5 μM of ZnPc 4 was toxic (70% cell survival). The uptake into Hep-2 cells was evaluated using 0.1 μM of sensitizer, reaching values of ∼0.05 nmol/10 6 cells after 3 h of incubation at 37 °C. The cell survival after irradiation of the cultures with visible light was dependent upon both light exposure level and intracellular sensitizer concentration. A higher photocytotoxic effect was found for ZnPc 3 with respect to 4 (32%/70% cell survival after 15 min of irradiation). Also, these studies were performed treating the cells with 0.5 μM of ZnPc 3. In this case, an increase in the uptake (∼0.28 nmol/10 6 cells) was observed, which is accompanied by a higher photocytotoxic activity (20% cell survival). These results show that even though both sensitizer present similar photophysical properties in homogeneous medium, the photodynamic behavior in cellular media can significantly be changed.
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