Acta chemica Scandinavica/Acta chemica Scandinavica. B, Organic chemistry and biochemistry/Acta chemica Scandinavica. A, Physical and inorganic chemistry/Acta chemica Scandinavica. Series B. Organic chemistry and biochemistry/Acta chemica Scandinavica. Series A, Physical and inorganic chemistry · 1999 · 29 citations · 0 references
PharmacyBiochemistryFood ScienceCarbohydrate ChemistryFood AnalysisFood ChemistryCalcium NutritionDrug SolubilityPolysaccharide PropertiesPolysaccharide StructureSolubility EnhancementSolubility OptimizationCalcium BiochemistryCalcium DissolutionPolysaccharide Natural ProductsSolubilitySolubility Products
The solubility products of the calcium salts of two polyhydroxy ligands (PHL), isosaccharinate (ISA) and gluconate (GLUC), were measured. Solubility products of log <em>K</em><sub>s,o</sub> = –6.22 ± 0.03 at <em>I </em>= 0 and <em>T</em> = 20 ± 1°C for Ca(α-ISA)<sub>2</sub>, and log <em>K</em><sub>s,o</sub> = –3.54 ± 0.06 at <em>I</em> = 0 and <em>T</em> = 20 ± 1 °C for Ca(GLUC)<sub>2</sub> were calculated ignoring the complexation equilibrium: Ca<sup>2+</sup> + PHL<sup>–</sup> ⇌ CaPHL<sup>+</sup>. If this complexation reaction is taken into account with log <em>K</em>°<sub>1</sub> = 1.7, the values of the solubility products are log <em>K</em><sub>s,o</sub> = –6.53 ± 0.02 at <em>I</em> = 0 for Ca(α-ISA)<sub>2</sub> and log <em>K</em><sub>s,o</sub> = –4.19 ± 0.05 at <em>I</em> = 0 for Ca(GLUC)<sub>2</sub>. Both dissolution reactions are endothermic. The standard free enthalpy change (Δ<em>H</em>°) for Ca(α-ISA)<sub>2</sub> is 40 ± 1 kJ mol<sup>–1</sup> and 37 ± 4 kJ mol<sup>–1</sup> for Ca(GLUC)<sub>2</sub>. The enthalpy was assumed to be constant in the temperature range 7<<em>T</em><90°C. The calculated standard entropy change (Δ<em>S</em>°) is 17 ± 5 J mol<sup>–1</sup> K<sup>–1</sup> for Ca(α-ISA)<sub>2</sub> and 60 ± 14 J mol<sup>–1</sup> K<sup>–1</sup> for Ca(GLUC)<sub>2</sub>.