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Photodynamic inactivation of microorganisms known as antibacterial photodynamic therapy (APDT) is one of the most promising and innovative approaches for the destruction of pathogenic microorganisms. Among the photosensitizers (PSs), compounds based on cationic porphyrins/metalloporphyrins are most successfully used to inactivate microorganisms. Series of meso-substituted cationic pyridylporphyrins and metalloporphyrins with various peripheral groups in the third and fourth positions of the pyrrole ring have been synthesized in Armenia. The aim of this work was to determine and test the most effective cationic porphyrins and metalloporphyrins with high photoactivity against Gram negative and Gram positive microorganisms. It was shown that the synthesized cationic pyridylporphyrins/metalloporphyrins exhibit a high degree of phototoxicity towards both types of bacteria, including the methicillin-resistant S. aureus strain. Zinc complexes of porphyrins are more phototoxic than metal-free porphyrin analogs. The effectiveness of these Zn–metalloporphyrins on bacteria is consistent with the level of singlet oxygen generation. It was found that the high antibacterial activity of the studied cationic porphyrins/metalloporphyrins depends on four factors: the presence in the porphyrin macrocycle of a positive charge (+4), a central metal atom (Zn[Formula: see text] and hydrophobic peripheral functional groups as well as high values of quantum yields of singlet oxygen. The results indicate that meso-substituted cationic pyridylporphyrins/metalloporphyrins can find wider application in photoinactivation of bacteria than anionic or neutral PSs usually used in APDT.

Photodynamic inactivation of some microorganisms (St. aureus, E.coli) was investigated and their dependence on photo-physical properties of photosensitizers (PS) (cationic porphyrins and metalloporphyrins) was shown. One of the most important criteria for the effectiveness of the PS`s is the quantum yield of singlet oxygen (γ ∆ ). Our investigations were shown that γ ∆ of metalloporphyrins, containing Zn, significantly higher than of metal-free porphyrins (85-97% and 77-79%, respectively). Previousl y experimentally we were found that under the action cationic porphyrins and metalloporphyrins on Gram (+) and Gram (-) microorganisms efficiency of metalloporphyrins Zn-TOEt4PyP and Zn-TBut4PyP in 3-5 times was higher than the metal-free porphyrins. In this study under the action of porphyrins and their Zn-derivatives on microorganism St. aureus such an effect was confirmed. Using the LED with a peak emission of 405 nm and a power density of 70 mW/cm 2 , and irradiation time of microorganisms from 5 to 30 minutes we have found, that at a concentration of 0.1 ug/ml the highest efficiency is observed of metalloporphyrin Zn-TBut3PyP. Upon irradiation of 10 and 15 min his efficiency is 3-5 times higher than the metal-free porphyrin TOEt4PyP, and irradiation for 30 min via Zn-TBut3PyP is practically completely kills microorganisms. These data correlate with the quantum yield of singlet oxygen for photosensitizers. The 30 mindirect sun exposure (power density of 70 mW/cm 2 ) of photosensitizer solutions showed that a significant photobleaching of porphyrins and metalloporphyrins does not occur. Thus, Zn-containing cationic metalloporphyrins are highly efficient photosensitizers for photodynamic inactivation of microorganisms and PDT.

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