Optical properties of a series of pyrrolyl-substituted porphyrazines and their photoinactivation potential against Enterococcus faecalis after incorporation into liposomes

Abstract

A series of porphyrazines substituted in the periphery with various pyrrolyl groups was studied regarding its optical properties and biological potential for antimicrobial photodynamic therapy towards Enterococcus faecalis. There were studied magnesium(II) porphyrazines with peripheral 2,5-dimethylpyrrol-1-yl, 2-methyl-5-phenylpyrrol-1-yl, 2,5-diphenylpyrrol-1-yl, 2,5-di(4′-chlorophenyl)pyrrol-1-yl, 2,5-di(biphenyl-4'-yl)pyrrol-1-yl, 2,3,5-triphenylpyrrol-1-yl substituents and zinc(II) porphyrazine substituted in the periphery with 2,5-dimethylpyrrol-1-yl groups. The studied photosensitizers revealed singlet oxygen quantum yield values in the range of 0.04–0.25, whereas fluorescence and photodecomposition quantum yield values were found between (0.45–4.55)·10−2 and (0.09–5.10)·10-4 respectively. For the studied group of porphyrazine randomers, it was noticed, that the non-alternating order of peripheral substituents can lead to the dramatic loss of their ability towards singlet oxygen formation and fluorescence emission. Replacing magnesium(II) with zinc(II) cation in the porphyrazine core also resulted in the significant improvement of the photoinactivation against Enterococcus faecalis with the log reduction value of >5.5 log. Magnesium porphyrazines revealed only weak or no activity against the studied bacterium.