Synthesis and photodynamic activity of zinc(II) phthalocyanine derivatives bearing methoxy and trifluoromethylbenzyloxy substituents in homogeneous and biological media

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.