In vitro photodynamic inactivation of B. subtilis and E. coli O157 by a new chalcone conjugate photosensitizer tethered with the NMe 2 group as fluorescence donor auxochrome

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Abstract 4-Azido-2,6-dimethylquinolie 2 was prepared and coupled under the CuAAC conditions with a set of propargylated chalcones 3a-e & 4a,b, and a ferrocene-chalcone conjugate 5. These couplings afforded a new series of tripod and tetrapod 1,4-disubstituted-1,2,3-triazoles 6a-e, 7a,b, and 8 for potential divergent applications. In vitro antimicrobial screening disclosed their negative antifungal activity against A. flavus and C. albicans. Similarly, they were inactive against S. aureus and E. coli except the chalcone 6e which was 39% as active as the antibiotics that target these organisms. Compound 6d displayed fluorescence in DMSO under the influence of 365 nm UV irradiation, absorption at λmax = 421 which falls within the blue range, and fluorescence emission at λmax = 523 nm. As photosensitizer (PS) of ROS in the presence of blue LED irradiation at a dose of 12 J/cm2, it displayed better in vitro photodynamic inactivation than antibiotics against B. subtilis and E. coli O157. The activity against the positive-type bacteria was better than the Gram-negative one due to penetration intolerance by the outer membrane of the negative type as displayed by the confocal microscope images. Therefore, the activity is attributed to intracellular bacterial poisoning by the photo-generated ROS rather than membrane disruption.

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