Solid-liquid equilibrium measurements on aqueous ternary systemscomposed of amino acids and tetraalkylammonium bromides

The solution behavior of amino acid + electrolyte aqueous systems provides valuableinformation about the complex behavior of proteins in biological systems [۱]. Further, ternarysolutions of {water + amino acid + solute ۲} could undergo the soluting-out phenomenon asaqueous biphasic systems formation [۲] or precipitation [۳]. In this respect, the liquid-liquid andsolid-liquid equilibria (LLE and SLE) studies are essential for designing, optimizing, and scalingup separation processes handling with amino acid-based systems. In this work, to obtainthermodynamic information about the soluting effect in aqueous ternary systems of amino acid +tetraalkylammonium bromide (TAAB) salt, solid-liquid equilibrium (SLE) behavior was studiedby measuring the solubility of tetramethylammonium bromide (TMAB) and tetrabutylammoniumbromide (TBAB) in aqueous solutions of S(-)-proline, as well as the solubility of S(+)-serine andS(-)-proline in aqueous solutions of TMAB. The SLE results revealed that the water-solubilitiesof TMAB and TBAB decrease in the presence of S(-)-proline, while the water-solubilities of theamino acids are not meaningfully affected by the addition of TMAB. The soluting-out coefficientobtained by correlating the solubility data with the Setschenow equation is positive and whosevalue for TBAB is more than TMAB. From the gathered results, the investigated amino acids(S(+)-serine and S(-)-proline) act as the soluting-out agent in amino acid + TAAB aqueoussolutions, and the strength of the soluting-out effect increases with increasing the differencebetween the hydrophobic character of the solutes.

کلیدواژه ها:

Solid-liquid equilibrium ، Soluting-out effect ، Amino acids ، Tetraalkylammonium salt