Halogenated Vitamin B 6 -Attached Co(III) Photosensitizers on Polypyridyl Scaffold for Light-Induced Antibacterial Activities

High Resolution Image Download MS PowerPoint Slide Four novel halogenated vitamin B 6 -derived Co(III) complexes viz., [Co(thio-tpy)(SBVB 6 )]Cl ( Co1 ), [Co(thio-tpy)(BrSBVB 6 )]Cl ( Co2 ), [Co(thio-tpy)(ClSBVB 6 )]Cl ( Co3 ), and [Co(thio-tpy)(FSBVB 6 )]Cl ( Co4 ), where 4′-(thiophen-2-yl)-2,2′:6′,2″-terpyridine = thio-tpy, ( E )-5-(hydroxymethyl)-4-(((2-hydroxyphenyl)imino)methyl)-2-methylpyridin-3-ol = H 2 SBVB 6, ( E )-4-(((5-bromo-2-hydroxyphenyl)imino)methyl)-5-(hydroxymethyl)-2-methylpyridin-3-ol = H 2 BrSBVB 6, ( E )-4-(((5-chloro-2-hydroxyphenyl)imino)methyl)-5-(hydroxymethyl)-2-methylpyridin-3-ol = H 2 ClSBVB 6, and ( E )-4-(((5-fluoro-2-hydroxyphenyl)imino)methyl)-5-(hydroxymethyl)-2-methylpyridin-3-ol = H 2 FSBVB 6 were developed successfully as potential photosensitizers for aPDT (antibacterial photodynamic therapy). The pronounced visible light absorption ( ca . 440–490 nm) and excellent stability under visible light render them suitable for aPDT applications. X-ray diffraction data of Co4 revealed a distorted octahedral Co III N 4 O 2 coordination core. Further, DFT and TD-DFT calculations provided insights into the electronic structure and HOMO–LUMO energy gaps. Interestingly, all complexes showed good 1 O 2 and • OH generation potential in a DMSO:H 2 O (1:99, v/v) under light. Under dark conditions, no notable antibacterial activity was observed; however, the activity was significantly enhanced upon exposure to 400–700 nm (10 J cm –2 ) light, particularly against Gram-positive bacteria ( Staphylococcus aureus ), with MIC values lying between 0.09 to 0.46 μg/mL, while no such effect was observed against the Gram-negative ( Escherichia coli ) bacteria. The light-activated antibacterial activity of Co1 – Co4 is likely attributed to their ability to disrupt bacterial cell membranes through reactive oxygen species (ROS)-mediated oxidative stress. Additionally, in silico molecular docking studies help to predict the possible mode of action, binding pattern, and interaction affinities between PBP2a and Co2 . Overall, these findings highlight the potential of halogenated vitamin B 6 -derived Co(III) complexes as promising next-generation photoresponsive antibacterial agents.