Hydration Thermodynamics and Hydrodynamic (Stokes) Radius of the Lanthanide Ions

Abstract

Many biochemical and physiological properties depend on the size of ions and the thermodynamic quantities of ion hydration. The diffusion coefficient (D) of lanthanide (III) ions (Ln⁺³) in solution assumed (1.558-1.618 ×10⁻⁹ m² s⁻¹) by Einstein–Smoluchowski relation. The association constant (K_A) of Ln⁺³ ions was calculated (210.3-215.3 dm³ mole^-1) using the Shedlovsky method, and the hydrodynamic radius calculated (1.515-1.569 ×10⁻¹⁰ m) by the Stokes-Einstein equation. The thermodynamic parameters (ΔG^o, ΔS^o) also calculated by used suitable relations, while ΔH^o, values are obtained from the literature. ΔG^o, for ion hydration, has negative values in the range (13.25-13.30 KJ/mole), and a negative ΔS^o, results have been shown in the limit (11.016-12.506 KJ/ K. mole).