A study on the solubility of some amino acids in (H2O + EtOH) and (H2O + EtOH + NaI) systems by gravimetric method at T = 298.15 K: Experimental measurements and COSMO-RS calculations

Abstract

In this study, the solubility of three amino acids including glycine, L-alanine, and L-valine was measured using the gravimetric method in aqueous mixtures with 0–100 % (w/w) ethanol in different salt concentrations of sodium iodide (from 0 to 2 mol kg−1) at 298.15 K and 89.1 kPa. The Setschenow equation was used to analyze the effect of the electrolyte on solubility. In addition, the multi-parameter Kamlet-Taft (KAT) equation was applied to provide detailed information on the solute–solvent and solvent–solvent interactions. Moreover, the molecular interactions in the solvent mixture were qualitatively investigated using the COSMO-RS method. The results showed that the solubility of each amino acid increases with increasing electrolyte concentration and decreases with increasing ethanol content in the solvent mixture. The Setschenow equation and experimental solubility data showed NaI's salting-in effect in the solubility process for all amino acids. It was found that the polarity-polarizability parameter of the solvent system has the most significant effect on the solubility of the amino acids. According to the COSMO-RS calculations, glycine and solvent system favor hydrogen bonding interactions while L-alanine and L-valine tend to interact with solvent more through hydrophobic interactions.