Tetrakis(thiadiazole)porphyrazines. 8. Singlet oxygen production, fluorescence response and liposomal incorporation of tetrakis(thiadiazole)porphyrazine macrocycles [TTDPzM] (M = MgII(H2O), ZnII, AlIIICl, GaIIICl, CdII, CuII, 2HI)

• Published in: Dalton transactions : an international journal of inorganic chemistry 2012, Vol.41 (2), p.6112-6121
• Main Authors: Pia Donzello, Maria, Viola, Elisa, Giustini, Mauro, Ercolani, Claudio, Monacelli, Fabrizio
• Format: Article
• Language: English
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c2dt12381a

The photoactivity for the generation of singlet oxygen, 1 O 2 , the key cytotoxic agent in the anticancer treatment known as photodynamic therapy (PDT), and the fluorescence response of the highly electron-deficient tetrakis(thiadiazole)porphyrazines of formula [TTDPzM] (M = Mg II (H 2 O), Zn II , Al III Cl, Ga III Cl, Cd II , Cu II , 2H I ) were examined ( c ≅ 10 −5 M) in dimethylformamide (DMF) and/or in DMF preacidified with HCl (DMF/HCl; [HCl] = 1-4 × 10 −4 M). The singlet oxygen quantum yield ( Φ Δ ) of all the compounds was determined by using a widely employed procedure based on the selective oxidation of the 1,3-diphenylisobenzofuran (DPBF), modified in part as reported. The list of the Φ Δ values indicates excellent photosensitizing properties for the series of compounds carrying "closed shell" metal ions, with values measured in DMF/HCl respectful of the "heavy atom effect" for the first four lighter centers, increasing in the order Mg II < Al III < Zn II < Ga III . Data of Φ Δ concerning the unmetalated species [TTDPzH 2 ], present in solution in the form of the corresponding anion [TTDPz] 2− , and the Cd II and Cu II complexes are also presented and discussed. Extensive discussion is also developed on the fluorescence quantum yield values Φ F , with data on the Mg II and Al III compounds in DMF/HCl (0.44 and 0.53, respectively) indicative of promising perspectives for applications in fluorescence imaging techniques. The Φ F data of the studied porphyrazine series, Φ F Pz , correlate linearly with those of the homologous phthalocyaninato complexes, Φ F Pc , suggesting a closely similar behaviour between the two classes of compounds. The incorporation of [TTDPzZn] into liposomes was successfully achieved following the detergent depletion method (DDM) from a mixed micellar solution by means of gel-filtration. Retention of [TTDPzZn] (∼40%) in its photoactive monomeric form into liposomes is proved by absorption and fluorescence spectra, this proposing the Zn II complex as a promising candidate for use in PDT. The present contribution reports on the singlet oxygen production, fluorescence response and liposomal incorporation of tetrakis(thiadiazole)porphyrazine macrocycles of formula [TTDPzM].