Thermodynamic characterization of proflavine–DNA binding through microcalorimetric studies

•Energetics of the interaction of proflavine with DNA has been studied.•The binding reaction was favored by both negative enthalpy and positive entropy.•Enthalpy–entropy compensation phenomenon was observed.•Non-polyelectrolytic forces played a dominant role in the binding process.•Proflavine enhanced the thermal stability of DNA remarkably.

The interaction of an important acridine dye, proflavine hydrochloride, with double stranded DNA was investigated using isothermal titration calorimetry and differential scanning calorimetry. The equilibrium constant for the binding reaction was calculated to be (1.60 ± 0.04) · 105 · M−1 at T = 298.15 K. The binding of proflavine hydrochloride to DNA was favored by both negative enthalpy and positive entropy contributions to the Gibbs energy. The equilibrium constant for the binding reaction decreased with increasing temperature. The standard molar enthalpy change became increasingly negative while the standard molar entropy change became less positive with rise in temperature. However, the standard molar Gibbs free energy change varied marginally suggesting the occurrence of enthalpy–entropy compensation phenomenon. The binding reaction was dominated by non-polyelectrolytic forces which remained virtually unchanged at all the salt concentrations studied. The binding also significantly increased the thermal stability of DNA against thermal denaturation.