Centrosymmetric paddlewheel copper(II) complexes as potent intercalators: synthesis, crystal structure description and DNA-binding studies

ABSTRACT Two copper(II) paddlewheel carboxylate complexes 1 and 2 of the general formula ACuL4CuA, where A is DMSO (1) and meta-bromopyridine (2) and L is meta-chlorophenyl acetate, have been synthesised, isolated quantitatively, crystallised and characterised using FTIR, UV-Visible spectroscopy, electrochemistry and XRD. FTIR spectra contained all the required peaks with the most prominent peaks those of carboxylate moiety indicating the bridging bidentate carboxylate binding mode. Electrochemistry yielded results typical of complexes containing Cu2+ centres. The structures were completely solved by XRD technique assigning square pyramidal geometry to each copper ion of the dinuclear complexes. The square base is formed by four oxygen atoms of the carboxylate moiety while the apical position is occupied by the fifth oxygen (of the DMSO molecule in 1) or nitrogen of the meta-bromopyridine in complex 2. The DNA-binding potency of the complexes was explored by viscometry, cyclic voltammetry, UV-Visible spectrophotometry and spectrofluorimetry. All these techniques provided coincident results and showed that the complexes bonded with DNA via an intercalative-binding mode. Additionally, these complexes were found to scavenge the free radical DPPH effectively. The complexes add interesting and valuable addition to the existing treasury on the copper paddlewheel complexes and their biological relevance. Graphical Abstract