Centro-symmetric paddlewheel copper(II) carboxylates: Synthesis, structural description, DNA-binding and molecular docking studies

The synthesis, structural characterization and biological relevance of three paddlewheel binuclear carboxylate copper(II) complexes with the formulae [Cu-2(2-nitrophenylacetate)(4) (H2O)(2)]C2H5OH (1), [Cu-2 (diclofenate)(4) (a-cetone)(2)] (2) and Cu-2(4-bromophenylacetate)(4) (pyridine)(2)] (3) have been presented here. These complexes have been characterized using melting point, FTIR, absorption spectroscopy, electron spin resonance, cyclic voltammetry (CV) and single crystal XRD techniques, while their biological relevance was ascertained using molecular docking and DNA-binding studies. The FTIR spectra indicated all the important functionalities and the typical bridging bidentate coordination mode of the carboxylate moieties to the copper ion. Absorption spectroscopy yielded broad spectra corresponding to the B-2(1g) ground state and the singly occupied d(x2)-( y2) orbital, typical of the copper(II) ion. This finding was confirmed by the ESR signals of complexes 1-3, with g values of 1.44353, 1.44317 and 1.44324, respectively. CV yielded redox couples typical of complexes with Cu2+ metal centers. XRD showed that the copper(II) ions in all three complexes are coordinated by four carboxylate ligands, constituting the square base of the square pyramid around each copper ion. The apical position is occupied by water (1), acetone (2) or pyridine (3) molecules. Owing to the structural differences, 1 and 3 have inter-molecular interactions and growth along all three axes, while 2 has such interactions only along the a-axis, leading to preferential growth along this axis. The structural parameters of the structures are different from each other and have been correlated mutually as well as with their literature analogues. Their supra-molecular synthons have been presented and explained. A computational study by molecular docking using MOE (molecular operating environment) software has yielded docking scores of -8.4098, -8.0453 and -9.4098, respectively for 1-3. The DNA-binding activity, explored via spectrophotometry and cyclic voltammetry, yielded intrinsic binding constant values of the order of 10(4) M-1 for all the complexes, showing excellent binding potency with DNA. The structural as well as biological importance of the complexes has been manifested.