Spectroscopic studies on the binding of holmium-1,10-phenanthroline complex with DNA

Fluorescence and absorption spectroscopy, circular dichroism (CD) as well as viscosity experiment have been used to characterize the DNA binding of [Ho(Phen)2Cl3]·H2O, where phen stand for 1,10-phanathroline. This complex exhibits the marked decrease in the emission intensity and some hypochromism in UV–Vis spectrum in the presence of DNA. For characterization of the binding mode between the Ho(III) complex and DNA various procedures such as: absorption and emission titration and EB quenching experiments, viscosity measurements, CD study, iodide quenching assay, salt effect and thermodynamical investigation are used. The intrinsic binding constant of [Ho(Phen)2Cl3]·H2O with DNA is calculated by UV–Vis and florescence spectroscopy. The value of binding constants in 296, 299 and 303 are 1.99 ± 0.07 × 104, 1.07 ± 0.09 × 104 and 0.84 ± 0.06 × 104, respectively. The thermodynamic studies show that the reaction is entropically driven. The above-mentioned physical measurements indicate that the Ho(III) complex binds to fish salmon DNA, presumably via groove binding mode.