The distribution of the charges on the sensitizer is another fact

The distribution of the charges on the sensitizer is another factor that influences

the efficiency of the PI process. In this study, the pattern Nepicastat manufacturer of inactivation by symmetric and asymmetric dicationic porphyrins was significantly different, although they both have a similar capaCity of producing singlet oxygen. Di-Py+-Me-Di-CO2H adj showed a higher efficiency on the photoinactivation of E. coli than Di-Py+-Me-Di-CO2H opp at the lower (0.5 μM) and highest (5.0 μM) concentrations. On E. faecalis, Di-Py+-Me-Di-CO2H adj it is also significantly different from Di-Py+-Me-Di-CO2H opp only when the lower concentration (0.5 μM) is used (p = 0.000, ANOVA). These results are in accordance with Kessel el al. (2003) studies that reported the cell localization and photodynamic efficacy of two dicationic porphyrins on Murine L 1210 cells. The PS with the two charges in adjacent positions was five-fold more efficient than the one with the charges in opposite positions [37]. The two adjacent positive charges in the porphyrin macrocycle should result in a molecular distortion due to electrostatic repulsion. In contrast, the porphyrin with the two opposite positive charges is a much more symmetric molecule. The affinity of these asymmetric cationic molecules with cell structures has yet to be established, but it is thought to be a function

of hydrophobiCity factors, charge distribution or both [37]. The Mono-Py+-Me-Tri-CO2H was the most inefficient PS against E. coli, causing a 3.28 log reduction on this strain and only after a total light dose of 64.8 J cm-2 (5.0 μM). This result is in agreement with previous studies where monocationic sensitizers were tested against Gram Metalloexopeptidase (-) bacteria [23, 24]. Conclusion The results obtained in this study show that the cationic porphyrins having three and four charges are highly efficient PS against both bacterial strains. The distinct meso-substituent groups in the porphyrin structure seem

to have different effects on PI. The Tri-Py+-Me-PF porphyrin provides the highest log reduction on cell survival using lower light doses. From this study and bearing in mind the development of efficient PS able to photoinactivate a large spectrum of environmental microorganisms, the Tri-Py+-Me-PF is the most promising PS. In addition, the PI of Gram (+) and also of Gram (-) bacteria using a higher bacterial density (107 CFU mL-1) than the levels present in wastewater (104–105 CFU mL-1) ensures its efficiency. Since this technology is to be used in the real context of a flow system and under solar light which is much more intense than the white light used in our studies (on average 456 W m-2 considering winter and summer periods in the City of Aveiro), the time needed for the photodynamic inactivation to occur would be substantially shorter. Therefore, this photodynamic approach applied to wastewater treatment under natural light conditions makes this technology cheap and feasible in terms of light source.

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