Abstract
The utilization of three methylene blue analogues containing hydroxyl functionalized auxochrome units (MBA) and their corresponding novel folic acid esters (FAE) as singlet-oxygen photosensitizers for antimicrobial photodynamic therapy (aPDT) was investigated. A new environmentally friendly ultrasoundassisted procedure for the synthesis of MBA and an optimized protocol for folic acid esterification are reported. Binding of folic acid to MBA did not alter the optical absorption/emission properties of the dyes, the folates exhibiting higher or at least equal fluorescence quantum yields when compared to those of the parent dyes. The photodynamic effect of MBA and FAE was evaluated based on their singlet oxygen generation capacity. The 1O2 quantum yields, determined by the indirect detection technique using 1,3-diphenylisobenzofuran (DPBF) as a sensor, appeared to be ∼ 50 % for MBA and decreased to ∼ 20 % in the case of FAE. The antimicrobial efficacy of the new FAE on four bacterial strains (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Deinococcus radiodurans) showed remarkable results especially when combined with photodynamic therapy.
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