A quaternary ammonium modified coumarin derivative for antimicrobial photodynamic therapy

A new cationic modified coumarin derivative, 7-diethylamino-3-(3-(4-(trimethylbenzenaminium iodide) phenyl) acryloyl)-2H-chromen-2-one ( 1 ), was synthesized and characterized by 1 H NMR and mass spectra. It had a strong intramolecular charge transfer absorption band around 460 nm with large molar extinction coefficients of 3.94 × 10 4 M -1 cm -1 in DMF and 3.86 × 10 4 M -1 cm -1 in PBS, respectively. Moreover, a moderate singlet oxygen quantum yield of 0.16 was obtained for 1 in DMF. Using methylene blue (MB) under a 630 nm laser as reference, the in vitro antimicrobial photodynamic therapy (aPDT) activity of 1 against three strains, gram positive bacteria methicillin-resistant staphylococcus aureus ( MRSA ), negative bacteria acinetobacter baumannii (A. baumannii ) and fungus Candida albicans (C. albicans ), was carried out by irradiation with a 457 nm laser. It was shown that 1 had no dark toxicity to these bacteria when its concentration was up to 100 μM, while under the 457 nm laser it could kill them effectively with an over 3 log CFU/ml decrease of the bacterial viability with its concentration up to 5 μM. The aPDT capability of 1 against MRSA and A. baumannii was equivalent to that of MB. For C. albicans , 1 exhibited much better aPDT effect than MB.