Thermodynamic analysis of the complexation of quinacrine with tRNAPhe

The thermodynamics of the interaction of the acridine derivative quinacrine with tRNAPhe was studied using isothermal titration calorimetry. The binding was monophasic and exothermic. At (298.15 ± 0.01) K the equilibrium constant was calculated to be (1.76 ± 0.70)·105 M−1. The binding stoichiometry was (0.15 ± 0.04). The binding was predominantly enthalpy driven (ΔHo = −28.39 ± 0.60 kJ·mol−1). Salt dependent ITC studies followed by dissection of the standard molar Gibbs energy change showed that the binding reaction was driven by both polyelectrolytic and non-polyelectrolytic forces with the non-polyelectrolytic forces being dominant. Temperature dependent ITC studies showed that the binding became increasingly enthalpy driven with rise in temperature. The binding was characterized by negative standard molar heat capacity change and enthalpy-entropy compensation behaviour.