Cobalt(II)–metformin complexes containing α‐diimine/α‐diamine as auxiliary ligand: DNA binding properties

Abstract

The cobalt(II) complexes [Co(Cl)2(met)(o‐phen)] (1), [Co(Cl)2(en)(met)] (2) and [Co(Cl)2(met)(opda)] (3) (met = metformin, o‐phen = ortho‐phenanthroline, en = ethylenediamine, opda = ortho‐phenylenediamine) were synthesized and characterized using liquid chromatography–mass spectrometry, elemental analysis, molar conductance measurements, thermal analysis, infrared spectroscopy, magnetic moment measurements, electronic spectroscopy and X‐ray diffraction. The metal centre was found to be in an octahedral geometry. UV–visible absorption, fluorescence and viscosity measurements were conducted to assess the interaction of the complexes with calf thymus DNA. The complexes showed absorption hyperchromism in UV–visible spectra with DNA. The binding constants from UV–visible absorption studies were 1.38 × 105, 2.1 × 105 and 3.1 × 105 M−1 for 1, 2 and 3, respectively, and Stern–Volmer quenching constants from fluorescence studies were 0.146, 0.176 and 0.475, respectively. Viscosity measurements revealed that the binding of the complexes with DNA could be surface binding, mainly due to groove binding. The activities of the complexes in DNA cleavage decrease in the order 3 > 2 > 1. The complexes were docked into DNA topoisomerase II using Discovery Studio 2.1 software.