Polypyridyl CoII-Curcumin Complexes as Photoactivated Anticancer and Antibacterial Agents

Four new Co^II complexes, Co(bpy)₂(acac)]Cl ( 1 ), Co(phen)₂(acac)]Cl ( 2 ), Co(bpy)₂(cur)]Cl ( 3 ), Co(phen)₂(cur)]Cl ( 4 ), where bpy=2,2’-bipyridine ( 1 and 3 ), phen=1,10-phenanthroline ( 2 and 4 ), acac = acetylacetonate ( 1 and 2 ), cur=curcumin monoanion ( 3 and 4 ) have been designed, synthesized and fully characterized. The X-ray crystal structures of 1 and 2 indicated that the CoN₄O₂ core has a distorted octahedral geometry. The photoactivity of these complexes was tuned by varying the π conjugation in the ligands. Curcumin complexes 3 and 4 had an intense absorption band near 435 nm, which made them useful as visible-light photodynamic therapy agents; they also showed fluorescence with λ_em≈565 nm. This fluorescence was useful for studying their intracellular uptake and localization in MCF-7 breast cancer cells. The acetylacetonate complexes ( 1 and 2 ) were used as control complexes to understand the role of curcumin. The white-light-triggered anticancer profiles of the cytosol targeting complexes 3 and 4 were investigated in detail. These non-dark toxic complexes displayed significant apoptotic photo-cytotoxicity (under visible light) against MCF-7 cells through ROS generation. The control complexes 1 and 2 did not induce significant cell death in the light or dark. Interestingly, 1-4 produced a remarkable antibacterial response upon light exposure. Overall, the reported results here can increase the boundary of the Co^II-based anticancer and antibacterial drug development.