Synthesis, structural characterization, DNA cleavage studies, antimicrobial activities, and time‐killing kinetics of tetranuclear Cu (II) with partial cubane Cu4O4 cores and mononuclear Co (II) and Ni (II) complexes of a new acylhydrazone ligand

Abstract

In the present study, a new acyl hydrazone N′‐(3‐ethoxy‐2‐hydroxybenzylidene)isobutyrohydrazide (ehbbhH2) and its metal complexes [Co (ehbbhH)2] (1), [Ni (ehbbhH)2] (2), and [Cu4(ehbbh)4]·4H2O (3) were prepared. The structure of the ligand was characterized using elemental analysis, GC‐MS, electronic, IR, 1H, and 13C NMR spectra. The structure of the prepared complexes was investigated by spectral, analytical, thermal, and magnetic susceptibility measurements. The results revealed that complexes 1 and 2 were formed in a 1 M:2 L mole ratio, whereas Complex 3 was formed in a 1:1 mole ratio. Spectral studies showed that the ligand in complexes 1 and 2 bonded to the metal ion in a monoanionic tridentate fashion through the azomethine nitrogen atom, carbonyl, and phenolic oxygen atoms. In Complex 3, ligand acted as dianionic tetradentate through the azomethine nitrogen atom, enolic, phenolic, and ethoxy oxygen atoms. The molecular structures of the ligand and Complex 3 were also established using single‐crystal X‐ray diffraction. The X‐ray structures of Complex 3 revealed that they contained a distorted Cu4O4 cubane core. The present study investigated the cleavage activities of the ligand and its complexes on supercoiled pBR322 DNA. Complex 3 was determined to be the most effective compound on pBR322 plasmid DNA in the presence of hydrogen peroxide. The antimicrobial activities of all compounds were investigated against two Gram‐positive bacteria, two Gram‐negative bacteria, and one eukaryote. The results showed that Complex 3 exhibited better antimicrobial activity than other complexes. Finally, time‐killing assays of Complex 3, which was the most effective complex, were carried out.