Designing, synthesis, spectral characterization of antimicrobial and DNA active tridentate Schiff base ligands and their complexes

Abstract

New neutral Schiff base tridentate ligand transition metal complexes of the composition, ML2, where M= Cu(II), Ni(II), Co(II) and Zn(II); L= ligands derived from semicarbazide hydrochloride and 2,4pentanedione/methyl acetoacetate/acetoacetanilide, were synthesized and characterized by elemental analyses, magnetic susceptibility, IR, UV-Vis., 1H-NMR, 13C-NMR, CV, ESR, and FAB-mass spectral techniques. Electronic absorption spectra of the complexes indicate an octahedral geometry around the metal ion. The magnetic susceptibility measurements and low conductance data provide evidence for the monomeric and neutral natures of the complexes respectively. The electrochemical behaviour, the anodic and cathodic potential and the number of electron transfer were calculated using cyclic voltammogram. The X-band ESR spectrum of copper complex in DMSO at 300 K and 77 K was recorded and its salient features are reported. The antimicrobial activities of the ligands and their complexes have been studied by screening the compounds against the bacteria E. coli, P.aeruginosa, P.mirabilis, S. typhi, and B.subtilis and also the fungi C.albicans and R. stolonifer and results have been compared with the standard drug, amphicillin. The data indicate that most of the metal complexes have higher antimicrobial activity than the free ligands and the standard. The DNA cleavage experiments, performed using gel electrophoresis with the corresponding metal complexes in the presence of H2O2 showed all the complexes afford a pronounced discernible DNA cleavage evidenced by the disappearance of Form I (supercoiled) of plasmid and the production of Form III (linear).