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

New Schiff base complexes [Cu(L1 )Cl] (1), [Ni(L1 )Cl] (2), [Zn(L1 )Cl] (3), and [Fe(L2 )H2 OCl] (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 1 H and 13 C 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 dx 2 - y 2 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 H2 O2 and on photo irradiation at 312nm.