DNA binding studies and antibacterial properties of a new Schiff base ligand containing homopiperazine and products of its reaction with Zn(II), Cu(II) and Co(II) metal ions: X-ray crystal structure of Cu(II) and Zn(II) complexes

In this paper, a new symmetrical, potentially hexadentate N4O2, macroacyclic Schiff base ligand (H2L) was derived from the condensation of a polyamine, 2,2'-((1,4-diazepane-1,4-diyl)bis(methylene))dianiline (A), with 2-hydroxybenzaldehyde. Three Schiff base complexes were prepared by direct reaction of H2L with Cu(II), Zn(II) and Co(II) ions in equimolar ratios. For Co(II), the metal was oxidized to Co(III), forming the six-coordinate complex with the desired Schiff base ligand [CoL]ClO4, however with Cu(II) and Zn(II) ions, the hydrolysis of the ligand occurred with the loss of one benzaldehyde group, resulting in the formation of the five-coordinate mono Schiff base ligand (HL'), with a N4O donor set. The products were characterized by several physicochemical measurements with the structures of the Cu(II) and Zn(II) complexes confirmed by single crystal X-ray structural analyses. As well, the DNA binding of H2L ligand and macroacyclic Schiff base complexes using UV-Vis absorption spectroscopy, competitive fluorescence, viscosity and gel electrophoresis measurements were studied. The UV-Vis spectra clearly indicated that all above compounds interact with calf thymus DNA (ct-DNA). Also, viscosity measurements and competitive fluorescence studies confirmed that they bind to ct-DNA via an inter-action mode. Also, the interaction of the ligand and its metal complexes with calf thymus DNA was explored using gel electrophoresis. The antibacterial activity of all synthesized compounds was tested against Gram-positive and Gram-negative bacteria. All synthesized compound showed an antibacterial activity against all bacterial species except Bacillus subtilis. (C) 2019 Elsevier Ltd. All rights reserved.