Synthesis, structural, electrochemical, DNA interaction, antimicrobial and molecular docking studies on dimeric copper(II) complexes involving some potential bidentate ligands

The dimeric copper(II) complexes [Cu-2(bpy)(2)(L-1)(2)(ClO4)(2)] (1), [Cu-2(biim)(2)(L-1)(2)(ClO4)(2)] (2), [Cu-2(bpy)(2) (L-2)(2)](ClO4)(2) (3) and [Cu-2(biim)(2)(L-2)(2)](ClO4)(2) (4) (where bpy = 2,2'-bipyridine, biim = 2,2'-biimidazole, L-1 = 5-methylsalicylaldehyde and L-2 = 5-bromosalicylic acid) have been synthesized and characterized by IR, UV-Vis, ESR and ESI-mass spectroscopy. The single crystal X-ray diffraction study of complexes 1 and 3 showed that the complexes crystallize in triclinic crystal system with the P (1) over bar space group. All the complexes showed one quasi-reversible redox wave in the cathodic region (E-PC(1)= -0.83 to -0.90 V), assignable to the Cu(II)/Cu(I) redox couple. The binding interaction of the complexes with calf thymus DNA (ctDNA) was investigated by absorption, fluorescence, circular dichroism spectral studies and molecular docking techniques. The copper(II) complexes showed good binding affinity to ctDNA and the intrinsic binding constants obtained from UV-Vis spectroscopic studies are 1.16 x 10(5), 3.19 x 10(5), 1.82 x 10(5) and 3.66 x 10(5) M-1 for complexes 1-4, respectively. The apparent binding constant obtained from fluorescence spectroscopic studies are 1.37 x 10(5), 3.33 x 10(5), 2.2 x 10(5) and 4.7 x 10(5) M-1 for the complexes 1-4, respectively. The copper(II) complexes showed efficient oxidative cleavage of plasmid pER322 DNA in the presence of 3-mercaptopropionic acid (MPA) and the cleavage process was found to proceed by a hydroxyl radical mechanism. The ligands and their Cu(II) complexes were screened for antimicrobial activities and the results indicated that the complexes exhibit significant antimicrobial activity compared to the free ligands. (C) 2014 Published by Elsevier Ltd.