Designing, structural elucidation, comparison of DNA cleavage, and antibacterial activity of metal(II) complexes containing tetradentate Schiff base

Macrocyclic complexes of Cu(II), Ni(II), Co(II), and Zn(II)of a tetradentate Schiff base ligand derived from 3-benzalideneacetoacetanilide and N-(2-aminoethyl)-1,3-ropanediamine were synthesized. The nature of the complexes and the geometry have been inferred from their microanalytical data, magnetic susceptibility measurements, IR, UV-Vis, 1H NMR, ESR, and mass spectral techniques. The low electrical conductance of the complexes supports the neutral nature. Monomeric nature of the complexes is assessed from their magnetic susceptibility values.The in vitro biological screening effects of the investigated compounds were tested against the bacteria E. coli, S. aureus, S. typhi, and K. pneumoniae by the well diffusion method using agar nutrient as the medium. A comparative study of minimum inhibitory concentration (MIC) values of the Schiff base and its complexes indicate that the metal complexes exhibit higher antibacterial activity than the free ligand and the control (streptomycin). The cyclic voltammetry method was used to probe the interaction of a Cu(II) complex with pUC18 DNA. Information of the binding ratio and intercalation mode can be obtained from its electrochemical data. Cyclic voltammetric measurements showed that the Cu(II) complex undergoes a reversible reduction at biologically accessible potentials. From the study, it is understood that the copper complex prefers to bind with DNA in Cu(II) rather than Cu(I) oxidation state. The DNA cleavage ability of the complexes was monitored by gel electrophoresis using supercoiled pUC18 DNA in tris-HCl buffer.