“On-Demand” Antimicrobial Photodynamic Activity through Supramolecular Photosensitizers Built with Rose Bengal and (p-Vinylbenzyl)triethylammomium Polycation Derivatives

Abstract

The antimicrobial photodynamic activity (aPDA) in fungal and bacterial strains of supramolecular adducts formed between the anionic photosensitizer (PS) Rose Bengal (RB 2− ) and aromatic polycations derived from (p-vinylbenzyl)triethylammonium chloride was evaluated. Stable supramolecular adducts with dissociation constants K d ≈ 5 μM showed photosensitizing properties suitable for generating singlet oxygen (Φ Δ = 0.5 ± 0.1) with the added advantage of improving the photostability of the xanthenic dye. However, the aPDA of both free and supramolecular RB 2− was highly dependent on the type of microorganism treated, indicating the importance of specific interactions between the different cell wall structures of the microbe and the PSs. Indeed, in the case of Gram-positive Staphylococcus aureus, the aPDA of molecular and supramolecular PSs was highly effective. Instead, in the case of Gram-negative Escherichia coli, only the RB 2− :polycation adducts showed aPDA, while RB 2− alone was inefficient, but in the case of Candida tropicalis, the opposite behavior was observed. Therefore, the present results indicate the potential of supramolecular chemistry to obtain aPDA àla carte depending on the target microbe and the PS properties.

Managing Corneal Infections: Out with the old, in with the new?

“…Green light with a peak absorption of 500–551 nm has been studied for its efficacy in aPDT along with the chemical substrate rose bengal (4,5,6,7-tetrachloro 2′,4′,5′,7′-tetraiodo). Rose bengal is a fluorescein derivative that absorbs light within the green spectral region (550 nm peak absorption) [ 92 ] and has been tested as a photosensitizer to eliminate cancer cells and for its anti-infective properties against numerous infectious agents [ 93 , 94 , 95 ], including those responsible for ocular infections [ 96 , 97 , 98 ]. Like many photosensitizers, it shows an affinity to Gram-positive bacteria, likely due to the lack of outer membrane that is characteristic of Gram-negative bacteria.…”