Synthesis, spectroscopic properties and interaction with a liposomal membrane of a novel iodinated magnesium phthalocyanine

• Mg tetraiodophthalocyanine is described with the purpose of applying it as a photosensitizer to eradicate cancerous cells.
• Magnesium phthalocyanine produces singlet oxygen and other reactive oxygen species with an excellent quantum yield of 0.95.
• It possesses the ability to penetrate lipid membranes of liposomes with binding constant equal Kb = 40.5 ± 6.4 (mg/mL)−1.
• Limited photostability of the dye is advantageous for the PDT to promote rapid breakdown and clearance after treatment.

Phthalocyanines are applied as effective photosensitizers in photodynamic therapy of cancer and some other diseases. In this study, the synthesis of magnesium 2,9(10),16(17),23(24)-tetraiodophthalocyanine (2) is described. The spectroscopic, photophysical and photochemical parameters of phthalocyanine 2 are discussed, including the ability of this novel photosensitizer to generate singlet oxygen (1O2). The quantum yield of singlet oxygen formation (ΦΔ) was determined by two methods, viz. by measuring time-resolved phosphorescence at 1270 nm and by using 1,3-diphenylisobenzofuran and 9,10-dimethylanthracene, the well-known chemical acceptors. Applying the first method, the value of ΦΔ in N,N-dimethylformamide was found to be 0.70 ± 0.02, while using the second method the quantum yield of singlet oxygen formation was found to be 0.95 ± 0.01. This discrepancy lead to the conclusion that the photooxidation process with phthalocyanine 2 as the photosensitizer proceeds via a mixed mechanism, viz. Type II and Type I and/or Type III. The fluorescence quantum yield of 2 in N,N-dimethylformamide is 0.063 ± 0.004. The interaction between photosensitizer 2 and liposomes in an aqueous suspension was studied using a laser scanning confocal microscopy and the fluorescence technique. It was found that the binding constant of phthalocyanine 2 to liposomes was equal Kb = 40.5 ± 6.4 (mg/mL)−1. This implies, that the studied photosensitizer can readily penetrate cell or lipid membranes.

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