Copper (II) Complexes of Knoevenagel Condensate β-Diketimines as Models for Blue Copper and their Interaction with DNA

Abstract

A series of copper(II) complexes with positive reduction potential have been synthesized by anin situfashion by the reaction of a Knoevenagel condensate, salicylidenebenzoylacetone (salbenz) with 4-X-anilines and copper(II) chloride. The electronic spectra of these complexes in acetonitrile show d–d bands around 540 nm with high molar extinction coefficient (ε~1600-1800 cm-1) due to lowering of symmetry around metal center, and MLCT band around 400 nm. The EPR spectral features with four g((lines having g((>2.0 >g⊥, and a broadening of g⊥component suggest a lowered site symmetry around Cu(II) monomer. The cyclic voltammetric studies of Cu(II) complexes in CH3CN shows a positive reduction potential (Epc = 492-451 mV) with moderately high peak to peak separation (∆Ep=126-163mV). All these results are comparable with the results of natural blue copper proteins even in the absence of S-coordination, and suggest that they can mimic the functional properties of blue copper proteins. These complexes on interaction with herring sperm DNA, the intense intraligand (IL) π-π*transition around 300 nm is found to be hypochromic with a slight red shift. The hypochromism and moderate binding constant are indicative of binding of the complexes with DNA with an affinity less than the classical intercalators, due to the possible substitution of the two chlorides with the DNA base pairs and relatively bulky structure of ligand molecule. Additional evidence of DNA-Cu(II) complex interaction was obtained by CD studies. The experimental results reveal that these complexes may serve as a model for blue copper proteins and as a tool for probing the structure of DNA.