Synthesis, Characterization, Molecular Docking, and Antibacterial Activity of a Novel Pyridine-Based Schiff Base and Its Copper(II), Silver(I), and Gold(III) Complexes

Cu(II), Ag(I), and Au(III) complexes were synthesized from a new organic Schiff base ligand (PMBD),4-(pyridin-3-ylimino)methyl) benzene-1,3-diol, derived from a pyridine heterocycle, and 2,4-dihydroxybenzaldehyde. Spectroscopy techniques, XRD, and SEM data confirmed that the ligand acts as a bidentate mono-deprotonated coordinator, yielding nanoparticle-sized complexes with octahedral, tetrahedral, and square planar structures, respectively. The antibacterial activity in vitro against Escherichia coli and Staphylococcus aureus using the agar well diffusion method, minimum inhibitory concentration (MIC), and minimum microbicidal concentration (MMC) tests was supported by computational work simulating molecular docking against DNA gyrase units (1KZN and 2XCS). The experimental results showed that synthesizing the metal complexes significantly enhanced antibacterial activity compared to the free Schiff base ligand. The Cu(II) complex showed the strongest activity, with the largest inhibition zones measuring 37 mm, followed by the Ag(I) complex (26 mm), and finally the Au(III) complex (14 mm). Computational molecular docking binding studies indicate that the [Cu(L)2(H2O)2] Complex has the highest affinity against E. coli (1KZN) with a binding score of -7.3 kcal/mol and the lowest Ki value (4.42 µM) compared to the free Schiff base ligand (Ki = 12.21 µM). Conversely, the [Au(L)Cl2] complex displayed a lower binding energy of (-5.4 kcal/mol) and a higher Ki (109.43 µM) against 2XCS, aligned with its reduced experimental potency. The synthesized Schiff base ligand and its metal complexes demonstrate promising in vitro and in silico antibacterial activities via potential DNA gyrase inhibition. These findings suggest their high potential for further development in pharmaceutical and industrial antimicrobial applications.