The naturally occurring photosensitizer curcumin has excellent biocompatibility, but its antimicrobial photodynamic efficacy is limited by (i) weak adherence to Gram(-) bacteria cell walls, (ii) low (photo-)stability and (iii) limited solubility in water. In this study novel curcuminoids bearing cationic substituents were prepared by different synthetic routes. The derivatives exhibit excellent water solubility, improved photostability and low aggregation. All novel curcuminoids showed antibacterial photodynamic effects (>3 log10 reduction of CFU) against Escherichia coli and Staphylococcus aureus upon blue light illumination. In contrast to natural curcumin, effective photokilling of E. coli was possible without the addition of permeabilizing agents. Ten micromolar of the most active compound (8) achieved a 7 log10 decrease of E. coli after light activation with a fluence of 33.8 J/cm2, whereas S. aureus was inactivated by more than 4 log10 at a fluence of 5.3 J/cm2. Overall the reduction in bacterial count was at least 100-fold more effective with these new curcuminoids in comparison to natural curcumin.
Keywords: Antimicrobial; Cationic photosensitizer; Curcumin; Diferoylmethane; Escherichia coli; Photodynamic Inactivation.
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