Copper(ii) complexes of salicylaldehydes and 2-hydroxyphenones: synthesis, structure, thermal decomposition study and interaction with calf-thymus DNA and albumins

Abstract

The neutral mononuclear copper(II) complexes with substituted salicylaldehyde (X-saloH), or 2-hydroxyphenone (ketoH) ligands, having the formula [Cu(L)₂(S)_n] (where S = solvent CH₃OH or H₂O and n = 0, 1 or 2) have been prepared and characterized, and their interaction with DNA and albumins was studied. The ligands are chelated to the metal ion through the phenolate and carbonyl oxygen atoms. The crystal structures of [Cu(5-NO₂-salo)₂(CH₃OH)₂] (3), [Cu(5-Cl-salo)₂] (4), [Cu(bpo)₂] (6) and [Cu(mpo)₂]·2H₂O (7·2H₂O) have been determined by X-ray crystallography. The thermal stability of the copper complexes has been investigated by a simultaneous TG/DTG-DTA technique. Spectroscopic (UV), electrochemical (cyclic voltammetry) and physicochemical (viscosity measurements) techniques have been employed in order to study the binding mode and strength of the complexes to calf-thymus (CT) DNA while competitive studies with ethidium bromide (EB) performed by fluorescence spectroscopy have revealed the ability of the complexes to displace the DNA-bound EB. In conclusion intercalation is the most possible mode of interaction of the complexes with CT DNA. The interaction of the complexes with serum albumin proteins has been studied by fluorescence emission spectroscopy and the determined binding constants exhibit relatively high values.