Thermodynamics of the weak interaction between samarium cation and xylitol in water: A chemical model

Abstract

The thermodynamic characterization of the weakly complexed model system Sm3+-xylitol has been carried out. The standard Gibbs energy enthalpy, entropy, volume and heat capacity of complexation of Sm3+ by xylitol have been determined in water at 25°. The stability constant and the enthalpy change have been simultaneously determined by using a calorimetric method. The thermodynamic properties characterizing solely the specific interaction between the cation and the complexing sequence of hydroxyl groups of the ligand have been isolated. The stability constant and the volume of complexation have also been estimated from a similar treatment of the apparent molar volumes. It was found that the reaction between Sm3+ and the complexing site of xylitol in water is characterized by: K = 8.1, ΔrGo = −5.2 kJ-mol−1, ΔrHo = −13.7 kJ-mol−1, TΔrSo = −8.5 kJ-mol−1, ΔrVo = 8.8 cm3-mol−1 and ΔrC p o = 51 J-K−1-mol−1.