Synthesis of two new N2O4 macroacyclic Schiff base ligands and their mononuclear complexes: Spectral, X-ray crystal structural, antibacterial and DNA cleavage activity

Abstract

Two new hexadentate N2O4 Schiff base ligands, H2L1 and H2L2, from condensation of 2-(2-((2-aminophenoxy)methyl)benzyloxy)benzenamine with 2-hydroxybenzaldehyde or 2-hydroxy-3-methoxybenzaldehyde, respectively have been prepared. From direct reaction of these ligands and Cu(II), Co(II), Ni(II) and Cd(II) metal salts in methanolic solution, the neutral [CuL1], [CoL1], [NiL1], [CdL1], [ZnL1], [CuL2], [CoL2], [NiL2], [CdL2] and [ZnL2] complexes were synthesized. These ligands and their complexes were characterized by elemental analysis, spectroscopic methods (UV–Vis, 1H, 13C NMR, EI-MS and IR). The conductivity data confirm the non-electrolytic nature of the all complexes. Also the crystal structure of [ZnL1], [NiL2] and [CoL2] complexes have also been determined by X-ray crystallographic technique. The Zn(II), Ni(II) and Co(II) complexes show a distorted octahedral configuration. The synthesized complexes have antibacterial activity against the three Gram-positive bacteria: Staphylococcus aureus, Enterococcus faecalis and Bacillus cereus and against the three Gram-negative bacteria: Escherichia coli, Proteus vulgaris and Pseudomonas aeruginosa and also against two yeast: Candida tropicalis and Candida albicans. The results showed that in some cases the antibacterial activity of complexes were more than Tetracycline and Natamycin as standards. The cleavage of DNA by all synthesized complexes were examined using gel electrophoresis experiments. The results showed that both of the Cu(II) complexes (except for 78μM [CuL1] complex) were completely broken structure of form I and form II DNA at all concentrations tested.