Thermodynamic Quantities of Transfer of Glycinato and β-Alaninato Complexes of Silver(I) and Related Species from Water to an Aqueous Dioxane Solution

Abstract

Abstract Complexation of silver(I) with glycinate (gly−) and β-alaninate (β-ala−) ions have been studied by potentiometry and calorimetry in 0.2 mole fraction (55.0 %w/w) dioxane–water mixture containing 3 mol dm−3 LiClO4 as a constant ionic medium at 25 °C. Potentiometric titration curves obtained were well-explained in terms of formation of [AgL], [AgL2]−, and [AgHL]+ (L−=gly− or β-ala−) in both systems, together with [Ag(OH)L]− in the Ag(I)–β-alanine system, and their formation constants were determined. Enthalpies of formation of the complexes in the mixed solvent, as well as in water containing the same ionic medium, were calorimetrically determined on the basis of the formation constants potentiometrically determined. Solubilities and enthalpies of solution of the neutral [AgL] (L−=gly− and β-ala−) complexes and some related compounds were determined in water and the mixture, the Gibbs energies of transfer, ΔGt°, of silver(I) ion and proton from water to the mixture being also determined by potentiometry. By combining the thermodynamic quantities thus obtained, thermodynamic quantities of transfer of single species from water to the mixture were evaluated. Compared to the enthalpy, ΔHt°, and entropy, ΔSt°, of transfer of a neutral species, the ΔHt° and ΔSt° values of any charged species were significantly large with the negative sign for cations and positive one for anions. As to neutral species, [HL] and [AgL], the relation, ΔGt°>ΔHt°≅0 and ΔSt°<0, was found, suggesting that the [AgL] complexes have a similar zwitterionic structure to that of glycine and β-alanine zwitterions.