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Issue 20, 2012
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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)

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Abstract

The photoactivity for the generation of singlet oxygen, 1O2, 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 = MgII(H2O), ZnII, AlIIICl, GaIIICl, CdII, CuII, 2HI) 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 (ΦΔ) 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 ΦΔ 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 MgII < AlIII < ZnII < GaIII. Data of ΦΔ concerning the unmetalated species [TTDPzH2], present in solution in the form of the corresponding anion [TTDPz]2−, and the CdII and CuII complexes are also presented and discussed. Extensive discussion is also developed on the fluorescence quantum yield values ΦF, with data on the MgII and AlIII compounds in DMF/HCl (0.44 and 0.53, respectively) indicative of promising perspectives for applications in fluorescence imaging techniques. The ΦF data of the studied porphyrazine series, ΦFPz, correlate linearly with those of the homologous phthalocyaninato complexes, ΦFPc, 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 ZnII complex as a promising candidate for use in PDT.

Graphical abstract: 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)

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Publication details

The article was received on 09 Dec 2011, accepted on 07 Mar 2012 and first published on 05 Apr 2012


Article type: Paper
DOI: 10.1039/C2DT12381A
Citation: Dalton Trans., 2012,41, 6112-6121
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    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)

    M. Pia Donzello, E. Viola, M. Giustini, C. Ercolani and F. Monacelli, Dalton Trans., 2012, 41, 6112
    DOI: 10.1039/C2DT12381A

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