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  • SCH 58261 br Results and Discussion br Spectral Properties o


    3. Results and Discussion
    3.1. Spectral Properties of ZnPcOC Complex in DMSO
    Metallophthalocyanine (MPc) complexes tend to aggregate in solu-tion and aggregation diminishes the photosensitising ability of MPc complexes. The association of these complexes could be reduced in such solvents as DMF, DMSO or ethyl alcohol [28]. Replacement of water  Journal of Photochemistry & Photobiology, B: Biology 190 (2019) 146–153
    molecules by organic solvent seems advantageous in such situation, because water strongly quenches singlet oxygen. The UV–Vis SCH 58261 spectra of the studied ZnPcOC showed a single and intense band at λmax = 692 nm accompanied by a next band of lower intensity at λmax = 620 nm (Fig. 1) in DMSO, while the B band was observed at 353 nm.
    In this solvent we observed a typical spectrum of a monomeric form of phthalocyanine, which is required for the use of this compounds in PDT. The ZnPcOC dissolved in DMSO fulfils the Lambert-Beer law in the range from 1⋅10−6 to 10⋅10−6 mol/l (Fig. 1). Determined value of the molar absorption coefficient in DMSO is 5,13 (log ε) and it is in the range typical for these kind of compounds.
    3.2. Photostability of ZnPcOC in DMSO
    Phthalocyanine compounds are usually thermally stable, chemically and light-resistant, however some of them are sensitive of UV light [29]. The photodegradation of phthalocyanine molecules can be ob-served by recording changes in Q and B bands. During the exposure of ZnPcOC in DMSO (685 nm visible light), slight changes of absorbance
    in time for Q band (λmax = 692 nm) was observed. However, the po-sition of Q and B bands did not change (Fig. 2). Moreover, the use of different radiation doses did not influence the photodegradation of zinc octacarboxyphthalocyanine. Regardless of the radiation dose (2.5; 4.5 and 7.5 J/cm2), the zinc octakarbox-yphthalocyanine photodegradation was approximately 2% over its in-itial value (Table 1).
    3.3. Luminescence Spectra
    The fluorescence properties of the studied phthalocyanine com-pound was examined in DMSO solution. The studied ZnPcOC exhibited a strong red fluorescence of 706 nm and the fluorescent form of the examined compound was the monomer of ZnPcOC. The Stokes shifts of the zinc octacarboxyphthalocyanine was estimated of 14 nm, as typi-cally observed for the phthalocyanine compounds. The absorption spectra were mirror images of the fluorescence spectra in DMSO solu-tion.
    The fluorescence intensity in DMSO strongly depended on the concentration of ZnPcOC and for concentrations ranging from 5.0⋅10−6 to 2.0⋅10−5 mol/l the dependence was nonlinear (Fig. 3). The maximal intensity was usually observed at concentration of about 1.0⋅10−5 mol/ l. For higher concentrations, the emission intensity decreased as the
    Fig. 2. UV–Vis spectra of ZnPcOC in DMSO before (−–) and after irradiation Fig. 3. Influence of ZnPcOC concentration on the fluorescence intensity in (···) (concentration of 5·10−6 mol/l, light intensity of 7.5 J/cm2, and tempera- DMSO. ture of 37 °C).
    ZnPcOC concentration increased and the curve slightly decreased. We concluded that the fluorescent form of ZnPcOC was the monomer, the association of which resulted in the observed luminescence decay. The dimer form and higher aggregates (multimers) of MPcOC were probably nonfluorescent [28].
    3.4. Biological Evaluation
    The obtained results showed intracellular accumulation of ZnPcOC after first 4 h of incubation with HaCaT, NHDF and Me45 cells, when final concentration in wells was 30 μM, whereas the second maximum of accumulation seemed to be after 72 h (Fig. 4). The absorbance at 690 nm, measured from washed with PBS cells, in each hour of ob-servation in 96 h assay, confirmed phthalocyanines accumulation. Spectra for visible light showed maximum at 690 nm, typically for ZnPcOC (Fig. 4; right), whereas empty control cells did not.