Porphyrin-polyethylenimine conjugates as photodynamic polymers to eliminate Staphylococcus aureus and Escherichia coli

Abstract

The increase in bacteria resistant to antibiotics in clinical use has led to the establishment of new treatments for infections. One of the proposed therapies includes photodynamic inactivation (PDI) of microorganisms. In this context, two novel polymeric conjugates, PEI-TPPF10 and PEI-TPPF20, were synthesized by the aromatic nucleophilic substitution reaction between polyethylenimine (PEI) and 5,15-di(4-N,N-dimethylaminophenyl)-10,20-di(pentafluorophenyl)porphyrin (TPPF10) or 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (TPPF20), respectively. The structures of these polymers were characterized by FTIR. UV–visible absorption and fluorescence studies indicated that the porphyrin units maintain their spectroscopic characteristics in the conjugates. The polymeric materials were able to produce singlet molecular oxygen and superoxide anion radical in solution. Furthermore, they were effective photosensitizers to photooxidize L-tryptophan and produce iodine in presence of iodide anions. The ability of these conjugates to photoinactivate bacteria was tested against Staphylococcus aureus and Escherichia coli. A reduction of 7 log (>99.9999 %) in cell survival was found after an irradiation with white light (90 mW/cm2) of 5 min (27 J/cm2) and 15 min (81 J/cm2), respectively. In these conjugates, the remaining amino groups are precursors of positive charges in the biological medium, favoring the interaction with microbial cells, which improves the photokilling activity. The results indicate that both conjugates are promising photosensitizing polymeric materials for the eradication of pathogens.