In vitro photodynamic activity of lipid vesicles with zinc phthalocyanine derivative against Enterococcus faecalis

Zinc(II) phthalocyanine bearing eight non-peripheral 2-propoxy substituents was subjected to physicochemical study and, after incorporation in lipid vesicles, assessed as a potential photosensitizer for antibacterial photodynamic therapy. The phthalocyanine derivative obtained in the macrocyclization reaction was characterized by MS and NMR techniques. Moreover, its chemical purity was confirmed by HPLC analysis. X-ray structural analysis revealed that overcrowding of the phthalocyanine derivative leads to a strong out-of-plane distortion of the π-system of the macrocycle core. In the UV-Vis absorption spectra of zinc(II) phthalocyanine two characteristic bands were found: the Soret (300-450 nm) and the Q band (600-800 nm). Photophysical properties of mono- and diprotonated forms of phthalocyanine derivative were studied with time-resolved fluorescence spectroscopy. Its tri- and tetraprotonated forms could not be obtained, because compound decomposes in higher acid concentrations. The presented zinc(II) phthalocyanine showed values of singlet oxygen generation Φ_Δ = 0.18 and 0.16, the quantum yield of the photodecomposition Φ_P = 3.06∙10^-4 and 1.23∙10^-5 and the quantum yield of fluorescence Φ_FL = 0.005 and 0.004, designated in DMF and DMSO, respectively. For biological studies, phthalocyanine has been incorporated into modified liposome vesicles containing ethanol. In vitro bacteria photoinactivation study revealed no activity against Escherichia coli and 5.7 log reduction of the Enterococcus faecalis growth.