Co(II), Ni(II), Cu(II) and Zn(II) Complexes of 1,8-Naphthalimide-based Ligand: Syntheses, Characterizations and Evaluation of Antibacterial Activities

Mononuclear later first-row transition metal complexes, [M(L)2] (1-4), where M = Co(II) (1), Ni(II) (2), Cu(II) (3), and Zn(II) (4) incorporating 1,8-naphthalimide based ligand were designed. The complex preparation was achieved by reacting metal nitrates with ligand (L) in 1:2 stoichiometry. The ligand and complexes were characterized with analytical and photophysical techniques. Single crystal X-ray diffraction determines that 3 is square planar. The complexes are highly fluorescent compared to the free ligand. The synthesized ligand (L) and complexes (1-4) were screened for their antibacterial activities against gram-positive [Streptococcus mutans (SM), Staphylococcus aureus (SA)] and gram-negative [Escherichia coli (EC), Klebsiella pneumoniae (KL)] bacterial strains. Ni(II) and Cu(II) complexes exhibited good activity against K. pneumonia and S. aureus compared to the free ligand. Particularly effective against gram-negative bacteria (Klebsiella pneumoniae), Ni(II) complex (2) has a MIC value of 6.25 mu M and exhibits similar activity to standard ciprofloxacin. Cu(II) complex (3) is two times more effective than the common antibiotic ciprofloxacin with a MIC value of 3.125 mu M against gram-positive bacteria (S. aureus).