title: 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.
authors.affiliation: Food Chemistry, Department of Food Science, University of Copenhagen , Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark.
authors.forename: Martina
authors.initials: M
authors.lastname: Vavrusova
authors.forename: Ran
authors.initials: R
authors.lastname: Liang
authors.forename: Leif H
authors.initials: LH
authors.lastname: Skibsted
mesh_terms: D002118:Calcium / Q000737:chemistry*; D017610:Calcium Compounds / Q000737:chemistry*; D003611:Dairy Products / Q000032:analysis; D004187:Disaccharides / Q000737:chemistry; D005942:Gluconates / Q000737:chemistry; D007773:Lactates / Q000737:chemistry*; D012995:Solubility; D012996:Solutions / Q000737:chemistry; D013649:Taste; D013696:Temperature; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
chemical_list: D017610:Calcium Compounds; D004187:Disaccharides; D005942:Gluconates; D007773:Lactates; D012996:Solutions; D014867:Water; C110051:calcium lactate; C005608:lactobionic acid; C030691:gluconic acid; D002118:Calcium