Polypyridyl-based Co(III) complexes of vitamin B Schiff base for photoactivated antibacterial therapy.

Herein, five novel polypyridyl-based Co(III) complexes of Schiff bases, , [Co(dpa)(L)]Cl (1), [Co(dpa)(L)]Cl (2), [Co(L)(L)]Cl (3), [Co(L)(L)]Cl (4), and [Co(L)(L)]Cl (5), where dpa (dipicolylamine) = bis(2-pyridylmethyl)amine; HL = ()-2-((2-hydroxybenzylidene)amino)phenol; HL = ()-5-(hydroxymethyl)-4-(((2-hydroxyphenyl)imino)methyl)-2-methylpyridin-3-ol; L = 4'-phenyl-2,2':6',2''-terpyridine (ph-tpy); and L = 4'-ferrocenyl-2,2':6',2''-terpyridine (Fc-tpy), were synthesized and characterized. Complexes 1, 3, and 4 were structurally characterized by single-crystal XRD, indicating an octahedral CoNO coordination core. The absorption bands of these complexes were observed in the visible range with a at ∼430-485 nm. Complex 5 displayed an extra absorption band near 545 nm because of a ferrocene moiety. These absorptions in the visible region reflect the potential of the complexes to act as visible-light antimicrobial photodynamic therapy (aPDT) agents. All of these complexes showed reactive oxygen species (ROS)-mediated antibacterial effects against (Gram-positive) and (Gram-negative bacteria) upon low-energy visible light (0.5 J cm, 400-700 nm) exposure. Additionally, 1-5 did not show any toxicity toward A549 (Human Lung adenocarcinoma) cells, reflecting their selective bacteria-killing abilities.