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

• Published in: Thermochimica acta 2005-04, Vol.428 (1), p.157-163
• Main Authors: Nazari, K., Golchin, A.R., Moosavi-Movahedi, A.A., Saboury, A.A., Hakimelahi, G.H., Shockravi, A., Tangestani-nejad, S.
• Format: Article
• Language: English
• Subjects: [pyda] 2[Co(phendc) 2]; Binding analysis; Biological and medical sciences; DNA; Enthalpy; Fundamental and applied biological sciences. Psychology; Interactions. Associations; Intermolecular phenomena; Ionization; Microcalorimetry; Molecular biophysics; Unfolding
• ISSN: 0040-6031; 1872-762X
• DOI: 10.1016/j.tca.2004.10.008

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.