Mixed-ligand copper(II) complexes of dipicolylamine and 1,10-phenanthrolines: The role of diimines in the interaction of the complexes with DNA

Abstract

Mixed-ligand copper(II) complexes of the type [Cu(dipica)(diimine)](ClO 4 ) 2 , where dipica is di(2-picolyl)amine and diimine is 1,10-phenanthroline (phen), 5,6-dimethyl-1,10-phenanthroline (5,6-dmp), 2,9-dimethyl-1,10-phenanthroline (2,9-dmp) or dipyridoquinoxaline (dpq), have been isolated and characterized by analytical and spectral methods. The copper(II) complexes exhibit a broad band in the visible region around 675 nm and axial EPR spectra in acetonitrile glass (77 K) with g || and A || values of ~2⋅22 and 185 × 10 -4 cm -1 respectively, suggesting the presence of a square-based coordination geometry for the CuN 5 chromophore involving strong axial interaction. The interaction of the complexes with CT DNA has been studied using absorption, emission and circular dichroic spectral methods and viscosity measurements. Absorption spectral titrations reveal that the intrinsic DNA binding affinities are dependent upon the nature of the diimine ligand: dpq > 5,6-dmp > phen > 2,9-dmp. This suggests the involvement of the diimine rather than the dipica 'face' of the complexes in DNA binding. An intercalative mode of DNA interaction, which involves the insertion of dpq and to a lesser extent the phen ring of the complexes in between the DNA base pairs, is proposed. However, interestingly, the 5,6-dmp complex is involved in hydrophobic interaction of the 5,6-dmp ring in the grooves of DNA. The large enhancement in the relative viscosity of DNA on binding to the dpq and 5,6-dmp complexes supports the proposed DNA binding modes. Further, remarkably, the 5,6-dmp complex is selective in exhibiting a positive-induced CD band on binding to DNA suggesting the transition of the B form of CT DNA to A-like conformation. The variation in relative emission intensities of DNA-bound ethidium bromide observed upon treatment with the complexes parallels the trend in DNA binding affinities.

Synthesis, characterization, antioxidant, antimicrobial, DNA binding and cleavage studies of mononuclear Cu(II) and Co(II) complexes of 3-hydroxy-N'-(2-hydroxybenzylidene)-2-naphthohydrazide

“…The binding constant Kb for complex 2 was found to be 6.6 x 10 4 M -1 at 268 nm, with the hypochromicity of about 10.34 %. The extent of hypochromism and red-shift observed for the mixed ligand complexes 1 and 2 are better comparing with the literature work [41,42] and lower than those observed for typical classical intercalators such as ethidium bromide (Kb, 1.4 x 10 6 M -1 in 25 mM Tris-HCl/40 mM NaCl buffer, pH = 7.9) [43] bound to CT DNA.…”

Template synthesis of novel carboxamide dinuclear copper (II) complex: spectral characterization and reactivity towards calf-thymus DNA

“…Furthermore, decrease in the intensity of DNA helicity band indicates the hydrophobic interaction of -NHgroups with DNA. Such spectral changes are characteristic of B to A conformational change (Ramakrishnan and Palaniandavar 2005). These CD spectral results support that the complex 1 interact with CT-DNA, and that the binding event induces certain conformational changes in DNA.…”

Binding and photocleavage of DNA by mixed ligand Co(III) and Ni(II) complexes of thiophene[2, 3-b] quinoline and phenanthrolie/bipyridine

“…A solution of calf thymus DNA in the buffer gave a ratio of UV absorbance at 260 and 280 nm about 1.8-1.9:1, indicating that the DNA was sufficiently free from protein (Ramakrishnan and Palaniandavar 2005). The concentration of CT-DNA was determined spectrophotometrically using the molar extinction coefficient at 6,000 M -1 cm -1 at 260 nm (Sasmal et al 2007).…”