Synthesis, photophysicochemical and photodynamic antimicrobial chemotherapy studies of indium pyridyl phthalocyanines: Charge versus bridging atom

2(3), 9(10), 16(17), 23(24)-Octapyridylsulfanyl phthalocyaninato chloroindium(III) (complex 1a) and its quaternized derivative 2(3), 9(10), 16(17), 23(24)-octamethylpyridylsulfanyl phthalocyaninato chloroindium (III) (complex 1b) were synthesised. The triplet quantum yields were 0.53 and 0.48 while the singlet oxygen quantum yields were 0.46 and 0.33 in DMF for 1a and 1b, respectively. The photodynamic antimicrobial chemotherapy (PACT) activity of 1b (containing 8 positive charges) was compared to those of 9(10),16(17),23(24)-tri-N-methyl-4-pyridylsulfanyl-2(3)-(4-aminophenoxy) phthalocyaninato chloro indium(III) triiodide (2) (containing 3 positive charges) and 2-[4-(N-Methylpyridyloxy) phthalocyaninato] chloroindium (III) iodide (3) (containing 4 positive charges). Complex 1b gave log reductions of 4.21, 8.30 and 3.21 for Gram(−) E. coli, Gram(+) S. aureus and C. albicans, respectively. When comparing 1b, 2 and 3, the largest log reductions for E. coli were obtained for complex 3 containing four positive charges hence showing it is not always the charge that determines the PACT activity, but the bridging atom in the phthalocyanine plays a role