Vitamin B₆ Appended Polypyridyl Co(III) Complexes for Photo‐Triggered Antibacterial Activity

Abstract

Three novel polypyridyl‐Co(III)‐vitamin B6 complexes viz., [Co(CF3‐phtpy)(SBVB6)]Cl (Co1), [Co(anthracene‐tpy)(SBVB6)]Cl (Co2), [Co(NMe2‐phtpy)(SBVB6)]Cl (Co3), where 4’‐(4‐(trifluoromethyl)phenyl)‐2,2’:6’,2’’‐terpyridine=CF3‐phtpy, 4’‐(anthracen‐9‐yl)‐2,2’:6’,2’’‐terpyridine=anthracene‐tpy;, 4‐([2,2’:6’,2’’‐terpyridin]‐4’‐yl)‐N,N‐dimethylaniline=NMe2‐phtpy, (E)‐5‐(hydroxymethyl)‐4‐(((2‐hydroxyphenyl)imino)methyl)‐2‐methylpyridin‐3‐ol=H2SBVB6 were successfully developed for aPDT (antibacterial photodynamic therapy) applications. Co1–Co3 exhibited an intense absorption band at ca. 435–485 nm, which is attributed to ligand‐to‐metal charge transfer and was beneficial for antibacterial photodynamic therapy. The distorted octahedral geometry of the complexes with CoIIIN4O2 core was evident from the DFT study. The visible light absorption ability and good photo‐stability of Co1–Co3 made them good photosensitizers for aPDT. Co1–Co3 displayed significant antibacterial responses against gram‐positive (S. aureus) and gram‐negative (E. coli) bacteria upon light exposure (10 J cm−2, 400–700 nm) and showed MIC values between 0.01–0.005 μg mL−1. The aPDT activities of these complexes were due to their ability to damage bacterial cell membranes via ROS generation. Overall, this study shows the photo‐triggered ROS‐mediated bacteria‐killing potential of Co(III) complexes.