Enhanced photoinduced antimicrobial properties of a copper(<scp>ii</scp>) polypyridine naphthalene diimide complex for wound infection treatment and biomolecular interactions

In this study, we synthesised and characterised a copper(II) naphthalenediimide-phenanthroline (NDI-Phen) compound and the corresponding copper complex. The photophysical properties of both the copper complex, Cu(NDI-Phen)Cl₂ (Cu1) and the <i>N</i>-octyl-<i>N</i>-[1,10]phenanthroline-1,4,5,8-naphthalenetetracarboxylic-diimide (NDI-Phen, L1) were probed using laser flash photolysis on the nano to microsecond timescales. The biological properties of the Cu1 complex and L1 were evaluated based on their interactions with DNA, bovine serum albumin (BSA), and their antimicrobial properties against clinically important pathogens were determined. The binding affinity of the Cu1 complex with calf thymus DNA (CT DNA) was evaluated using UV-Vis absorption titrations, and fluorescence quenching measurements. The results indicate a stronger intercalative binding mode for the copper complex, compared to L1, suggesting enhanced stabilisation with the DNA helix. The interaction with BSA was also studied for the Cu1 complex, which exhibited a higher quenching and binding constant compared to L1. This suggests a stronger and more stable interaction with the protein, which may improve its bioavailability and resistance to degradation under physiological conditions. The Cu1 complex demonstrated superior antibacterial activity when compared to L1. These findings suggest that complexation of the NDI-Phen unit with a copper centre significantly improves its potential as an antibacterial agent.