Microcalorimetry and binding studies of DNA upon interaction with [pyridine diamine]2[Co(phenanthroline dicarboxylate)2]

Abstract The interaction of calf thymus DNA with [pyridine diamine] 2 [Co(phenanthroline dicarboxylate) 2 ], [ pyda ] 2 [ Co ( phendc ) 2 ], complex has been studied at 10 mM phosphate buffer at 27 °C, pH 7.0 using various techniques including isothermal titration calorimetry (ITC), UV–vis spectrophotometry and potentiometric titration. Sigmoidal absorption profile implies the existence of cooperative interactions between DNA and [pyda] 2 [Co(phendc) 2 ] that induces a conformational change in DNA structure. Scatchard plots confirm this cooperative interaction. The calorimetric enthalpy curve of [pyda] 2 [Co(phendc) 2 ] upon interaction with DNA is measured by ITC. The enthalpy of binding (Δ H bin ) of [pyda] 2 [Co(phendc) 2 ] with DNA is also obtained spectrophotometrically by determining of equilibrium binding constants at 27 and 37 °C based on Wyman binding potential and van’t Hoff relation. The enthalpy of ionization (Δ H ion ) is also obtained by acid–base titration at 27 and 37 °C in 100 mM KCl solution using modified differential van’t Hoff relation for estimation of (Δ H ion ). The binding data was analyzed in a two-set binding sites model based on the Hill equation. The first phase of the calorimetric enthalpy curve is consistent with a first set of binding sites and further phases are consistent with a second set of binding sites.