Thermodynamic quantities for the interaction of the anticancer dietary pigment curcumin with human serum albumin were measured by using isothermal titration calorimetry. The equilibrium constant of the complex formation at T = 293.15 K was found to be (5.25 +/- 0.05) 10(5) M-1. The binding was exothermic with T Delta S degrees = (24.82 +/- 0.01) kJ . mol(-1), where Delta S degrees is the standard molar entropy change and Delta H degrees = -(7.28 +/- 0.04) kJ . mol(-1), where Delta H degrees is the standard molar enthalpy change. The stoichiometry of binding was established to be 1:1. The equilibrium constant decreased with increasing Na+ concentration. The equilibrium constant decreased from (5.25 +/- 0.05) . 10(5) M-1 to (2.88 +/- 0.03) . 10(5) M-1 by increasing the salt concentration from (10 to 50) mM. Both polyelectrolytic and non-polyelectrolytic forces contributed to the standard molar Gibbs free energy change. However the contribution from the latter was dominant and almost invariant at all Na+ concentrations. The negative standard molar heat capacity change along with significant enthalpy-entropy compensation suggests the involvement of multiple weak non-covalent forces in the binding process. (C) 2013 Elsevier Ltd. All rights reserved.