Photodynamic antimicrobial chemotherapy activity studies of 3-pyridyl substituted tetraarylchlorins and tetraarylbacteriochlorins

The photodynamic antimicrobial chemotherapy activity (PACT) properties of 3-pyridyl substituted tetraarylchlorin ( Chl1 ) and tetraarylbacteriochlorin ( BChl1 ) have been assessed against Gram-(+) S. aureus and Gram-(−) E. coli strains. The pyridyl nitrogens were quaternized with methyl iodide to form water-soluble tetracationic species ( Chl1-Q and BChl1-Q ) that are more suitable for use against Gram-(−) bacteria. Metal insertion reactions with a main-group heavy-atom ion, Sn(IV), were attempted to assess whether the singlet oxygen quantum yield and the PACT activity properties could be enhanced in this manner. This proved successful with the chlorin ligand ( Sn IV Chl1 ), but purification and characterization was problematic in the context of the bacteriochlorin. Upon photoirradiation with Thorlabs LEDs, Chl1 and Chl1-Q exhibited high Log 10 reduction values of 8.98 against S. aureus , while Sn IV Chl1 exhibited Log 10 reduction of 8.96 and 8.98 against both S. aureus and E. coli . This is noteworthy since neutral photosensitizers are normally ineffective against Gram-(−) strains. The cationic BChl1-Q species exhibits favorable photocytotoxicity towards S. aureus with a Log 10 reduction value of 6.61.