Thermodynamics of Dissolution of Calcium Hydroxycarboxylates in Water

Abstract

Aqueous solubility of calcium l-lactate, calcium d-gluconate, and calcium d-lactobionate increases with temperature (10-30 °C investigated), most significantly for the least soluble d-gluconate, while the calcium ion activity of the saturated solutions decreases with temperature, as measured electrochemically, most significantly for the most soluble d-lactobionate. This unusual behavior is discussed in relation to dairy processing and explained by endothermic binding of calcium to hydroxycarboxylate anions determined to have ΔH°ass = (31 ± 3) kJ·mol(-1) for l-lactate, (34 ± 2) kJ·mol(-1) for d-gluconate, and (29 ± 3) kJ·mol(-1) for d-lactobionate in 1:1 complexes with thermodynamic binding constants at 25 °C of Kass = 49 (l-lactate), 88 (d-gluconate), and 140 (d-lactobionate). Quantum mechanical calculations within density functional theory (DFT) confirm the ordering of strength of binding. The complex formation is entropy driven with ΔS°ass> 0, resulting in decreasing calcium ion activity in aqueous solutions for increasing temperature, even for the saturated solutions despite increasing solubility.

Spontaneous supersaturation of calcium citrate from simultaneous isothermal dissolution of sodium citrate and sparingly soluble calcium hydroxycarboxylates in water

“…The thermodynamic association constants are valid for ion activities as they were determined by extrapolation to zero ionic strength. 9,15 For the supersaturated solutions with ionic strength higher than unity concentration based association constants will have to replace the activity based association constants for quantitative calculations. The use of equilibrium constants determined for 1.0 M KCl or NaCl seems an acceptable approximation, since ionic strength in most of the supersaturated and the equilibrated solutions are close to unity.…”

“…where g 2+ is the activity coefficient calculated from the Davies' equation as described previously 15 log…”

Towards a low CO2 emission building material employing bacterial metabolism in a two-step process of limestone dissolution and recrystallization: The bacterial system and prototype production

“…Vavrusova et al [20]. Calculations were made for both, open systems, with the fluid in equilibrium with an atmospheric pCO2 of 10 -3.5 atm, and closed systems without CO2 exchange with the atmosphere.…”

The Structure and Thermal Properties of Solid Ternary Compounds Forming with Ca2+, Al3+ and Heptagluconate Ions

“…The solution equilibria between sugar-type ligands (such as gluconate, gulonate, heptagluconate, isosaccharinate) and Ca 2+ or Al 3+ ions in acidic to neutral medium have been by now well established [ 8 , 9 , 10 , 11 , 12 , 13 , 14 ]. Additionally, complexation reactions in strongly alkaline medium have been quantified and deep understanding on metal-ligand interactions have been gained [ 15 , 16 , 17 ].…”