Acid–base effects, light emission, DNA-binding and photocleavage studies of oligo-homonuclear ruthenium(II) complexes and their computational study

Comparative Studies on DNA-Binding Mechanisms between Enantiomers of a Polypyridyl Ruthenium(II) Complex

A pair of ruthenium(II) complex enantiomers, Δ- and Λ-[Ru(bpy)₂MBIP]²⁺ (bpy = 2,2'-bipyridine, MBIP = 2-(3-bromophenyl)imidazo[5,6-f]phenanthroline), were designed, synthesized, and characterized. Comparative studies between the enantiomers on their binding behaviors to calf thymus DNA (CT-DNA) were conducted using UV-visible, fluorescence, and circular dichroism spectroscopies, viscosity measurements, isothermal titration calorimetry, a photocleavage experiment, and molecular simulation. The experimental results indicated that both the enantiomers spontaneously bound to CT-DNA through intercalation stabilized by the van der Waals force or the hydrogen bond and driven by enthalpy and that Δ-[Ru(bpy)₂MBIP]²⁺ intercalated into DNA more deeply than Λ-[Ru(bpy)₂MBIP]²⁺ did and exhibited a better DNA photocleavage ability. Molecular simulation further indicated that Δ-[Ru(bpy)₂MBIP]²⁺ more preferentially intercalated between the base pairs of CT-DNA to the major groove, and Λ-[Ru(bpy)₂MBIP]²⁺ more favorably intercalated to the minor groove. These research findings should be very helpful to the understanding of the stereoselectivity mechanism of DNA-bindings of metal complexes, and be useful for the design of novel metal-complex-based antitumor drugs with higher efficacy and lower toxicity.

Cu(I) complexes of bis(methyl)(thia/selena) salen ligands: Synthesis, characterization, redox behavior and DNA binding studies

Mononuclear cuprous complexes 1 and 2, [{CH₃E(o-C₆H₄)CH=NCH₂}₂Cu]ClO₄; E=S/Se, have been synthesized by the reaction of bis(methyl)(thia/selena) salen ligands and [Cu(CH₃CN)₄]ClO₄. Both the products were characterized by elemental analysis, ESI-MS, FT-IR, ¹H/¹³C/⁷⁷Se NMR, and cyclic voltammetry. The complexes possess tetrahedral geometry around metal center with the N₂S₂/N₂Se₂ coordination core. Cyclic voltammograms of complexes 1 and 2 displayed reversible anodic waves at E_1/2=+0.08V and +0.10V, respectively, corresponding to the Cu(I)/Cu(II) redox couple. DNA binding studies of both the complexes were performed applying absorbance, fluorescence and molecular docking techniques. Competitive binding experiment of complexes with ct-DNA against ethidium bromide is performed to predict the mode of binding. The results indicate the groove binding mode of complexes 1 and 2 to DNA. The binding constants revealed the strong binding affinity of complexes towards ct-DNA.