Ibrahim Waziri1*, Mercy S. Ogunmodede1,2, Grema A. Mala1, Bala Isa3, Abubakar A. Ahmed1, Hussaini B. Adam3 , and Salihu A. Musa
1Department of Pure and Applied Chemistry, University of Maiduguri, P.M.B. 1069, Maiduguri, Borno State, Nigeria
2Department of Chemistry, Faculty of Natural and Applied Sciences, Nigerian Army University, Biu, P.M.B. 1500, Biu, Borno State, Nigeria
3Department of Chemistry, Borno State University, Maiduguri, Borno state, Nigeria
*Corresponding author’s Email: triumph2236@gmail.com, doi.org/10.55639/607.02010036
ABSTRACT
Metal complexes derived from Schiff bases ligands stand at the forefront of research aiming to develop precise and potent therapeutic agents, owing to their exceptional effectiveness. In this study, naphthaldehyde-derived Schiff base Ligand (HL) was synthesized via a mechanochemical reaction between 2-hydroxy-1-naphthaldehyde and 4-iodoaniline. Subsequently, the ligand was further reacted with Ni(II) and Cu(II) ions using their respective metal salts to obtain homoleptic mononuclear complexes (C1 and C2). The composition of HL, C1, and C2 were determined using 1H and 13C NMR, UV-Vis, FTIR, CHN, and HRMS analyses. The results of these analyses revealed the ligand acted as bidentate mono-negative and chelate the metal ions through oxygen and nitrogen atoms of phenolate and azomethine moieties. Furthermore, the antibacterial potential of HL, C1, and C2 was assessed using in vitro disc diffusion techniques against selected bacteria, including Gram-positive Staphylococcus aureus and Streptococcus pyogenes, and Gram-negative Escherichia coli and Klebsiella pneumoniae, at concentration ranges of 10, 20, and 30 μg/mL, in comparison to the positive control (ciprofloxacin). The antibacterial study demonstrated concentration-dependent activity, with the complexes surpassing the ligand in effectiveness against all tested bacteria at all concentrations. Notably, the Cu(II) complex, C2, exhibited superior activity compared to the Ni(II) complex, C1. C2 recorded higher zone of inhibition of 30.0±0.05 mm and 28.0±0.05 mm on S. aureus and E. coli, respectively. These findings establish a robust foundation for further refining the lead compound to unlock its therapeutic potential in addressing the escalating challenge of bacterial resistance to antibiotics.
Keywords:
Metal complexes,
Schiff base,
Antimicrobial,
Mechanochemical synthesis