The solubilities of glycine, L-leucine, L-phenylalanine,
and L-aspartic acid were measured in aqueous MgCl2,
Mg(NO3)2, CaCl2,, and Ca(NO3)2 solutions with concentrations
ranging from 0 to 2 mol/kg at 298.2 K. The isothermal analytical
method was used combined with the refractive index measurements
for composition analysis guaranteeing good accuracy. All
salts induced a salting-in effect with a higher magnitude for those
containing the Ca2+ cation. The nitrate anions also showed
stronger binding with the amino acids, thus increasing their relative
solubility more than the chloride anions. In particular, calcium
nitrate induces an increase in the amino acid solubility from 2.4
(glycine) to 4.6 fold (L-aspartic acid) compared to the
corresponding value in water. Amino acid solubility data in
aqueous MgCl2 and CaCl2 solutions collected from the open literature were combined with that from this work, allowing us to
analyze the relations between the amino acid structure and the salting-in magnitude.
This work was developed within the scope of the project CIMO-Mountain Research Center, UIDB/00690/2020 and LA/P/0007/2020 and CICECO-Aveiro Institute of Materials, UIDB/50011/2020 & UIDP/50011/2020 and LA/P/0006/2020, financed by national funds through the Portuguese Foundation for Science and Technology (FCT)/MCTES.
Mehriban Alyieva thanks FCT and European Social Fund (ESF) for her Ph.D. grant (SFRH/BD/139355/2018).
