BODIPYs are versatile dyes never tested before in photodynamic application against prokaryotes. We specifically synthesized two cationic BODIPYs (compounds 3 and 4) with structural features suitable for this pourpose. The novel BODIPYs are both characterized by the presence of one pyridinium cationic group on position 8 and two iodine atoms on 2,6-positions of the dipyrrolylmethene structure, thus ensuring solubility in 1/1 water/organic solvent mixture and a good singlet oxygen formation rate. These two photosensitizers differ only in the moiety linked on pyridine nitrogen atom as 3 and 4 bear a methyl and a benzyl group, respectively. BODIPYs 3 and 4 were tested against two bacterial model strains, the Gram positive Staphylococcus xylosus and the Gram negative Escherichia coli. Despite the small structural modification between 3 and 4, a remarkable difference in photocatalyzed efficacy against the model microorganisms was observed. In particular methylated compound 3 was found much more efficient with respect to the benzylated one (4). As consequence, in-depth examination of the antibacterial activity was performed using the more efficient compound 3. A high degree of phototoxicity (>6 log units) was observed with the photosensitizer 0.5 lM against S. xylosus and 5.0 lM against E. coli, following 5 min irradiation with a green LED device (light dose 1.38 J/cm2). No dark toxicity was observed up to 40 lM. Further studies indicate that the phototoxic efficacy induced by BODIPY 3 depends both on its concentration and on light dose, which can be specifically modulated to achieve the eradication of the tester strains.
Synthesis and antibacterial activity of novel cationic BODIPY photosensitizers
CARUSO, ENRICO;BANFI, STEFANO;BARBIERI, PAOLA;ORLANDI, VIVIANA TERESA
2012-01-01
Abstract
BODIPYs are versatile dyes never tested before in photodynamic application against prokaryotes. We specifically synthesized two cationic BODIPYs (compounds 3 and 4) with structural features suitable for this pourpose. The novel BODIPYs are both characterized by the presence of one pyridinium cationic group on position 8 and two iodine atoms on 2,6-positions of the dipyrrolylmethene structure, thus ensuring solubility in 1/1 water/organic solvent mixture and a good singlet oxygen formation rate. These two photosensitizers differ only in the moiety linked on pyridine nitrogen atom as 3 and 4 bear a methyl and a benzyl group, respectively. BODIPYs 3 and 4 were tested against two bacterial model strains, the Gram positive Staphylococcus xylosus and the Gram negative Escherichia coli. Despite the small structural modification between 3 and 4, a remarkable difference in photocatalyzed efficacy against the model microorganisms was observed. In particular methylated compound 3 was found much more efficient with respect to the benzylated one (4). As consequence, in-depth examination of the antibacterial activity was performed using the more efficient compound 3. A high degree of phototoxicity (>6 log units) was observed with the photosensitizer 0.5 lM against S. xylosus and 5.0 lM against E. coli, following 5 min irradiation with a green LED device (light dose 1.38 J/cm2). No dark toxicity was observed up to 40 lM. Further studies indicate that the phototoxic efficacy induced by BODIPY 3 depends both on its concentration and on light dose, which can be specifically modulated to achieve the eradication of the tester strains.
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