Non-enolisable Knoevenagel condensate appended Schiff bases-metal (II) complexes: Spectral characteristics, DNA-binding and nuclease activities

Abstract

New Schiff base complexes [Cu(L1)Cl] (1), [Ni(L1)Cl] (2), [Zn(L1)Cl] (3), and [Fe(L2)H2OCl] (4) {L1=(4E)-3-(2-hydroxybenzylidene)-4-(2-hydroxyphenylimino)pentan-2-one, L2=2,2′-(1E,1′E)-(3-(2-hydroxybenzylidene)-pentane-2,4-diylidene)bis(azan-1-yl-1 idene)diphenol} have been synthesized and characterized by elemental analysis, UV–Vis, IR, FAB-mass, EPR, spectral studies and electrochemical studies, the ligands L1 &L2 were characterized by 1H and 13C NMR spectra. Complex 1 show a visible spectral d-d band near 600nm and display cyclic voltammetric quasireversible response for the Cu(II)/Cu(I) couple vs Ag/AgCl in DMSO. The EPR spectrum of 1 show g‖>g⊥ suggesting a square planar geometry around copper with dx2−y2 as the ground state. The mass spectral results have confirmed the proposed structure for complexes 1–4. DNA binding properties of these complexes 1–4 have been investigated by absorption titrations, cyclic voltammetric studies and circular dichroism studies. On titration with DNA, the complexes 1–4 show hypochromism at the MLCT band (13–31%) with a red shift of 1–8nm in the electronic spectrum and positive shift of voltammetric E1/2 in the CV studies are in favour of intercalative binding. CD spectra of 1 showed an increase in molar ellipticity (θ278) of the positive band with a minor red shift indicating the transition of B-form of DNA to A like form. DNA cleavage studies of complexes 1 and 4 with pUC18 DNA were studied by gel electrophoresis and complex 4 cleaves supercoiled pUC18 DNA in an oxidative manner in the presence of H2O2 and on photo irradiation at 312nm.