Soluting-out effect of amino acids on aqueous solutions oftetraalkylammonium salts revealed by isopiestic measurements

Tetraalkylammonium (TAA) salts are used in many environmental and biological processesbecause of possessing both ionic and hydrophobic properties [۱]. The possibility of evaluating theeffects of TAA salt’s alkyl chain length and anion type on the interactions governing the solutionbehavior causes TAA salts to be a good choice for investigating the soluting effects occurring inaqueous solutions containing another solute [۲,۳]. In order to expand the knowledge of the solutingout/in phenomena occurring in aqueous solutions, in this work, several ternary systems of {water +amino acid + quaternary ammonium salt} were subjected to isopiestic (vapor-liquid equilibrium(VLE)) measurements at ۲۹۸.۱ K. The amino acids used are glycine, DL-alanine, S(+)-serine, and S(-)-proline and the tetraalkylammonium salts are tetramethylammonium bromide (TMAB),tetrapropylammonium bromide (TPAB), tetra-n-butylammonium bromide (TBAB), tetra-nbutylammoniumchloride (TBAC), and tetra-n-butylammonium hydrogen sulfate (TBAH). Thedeviations of water iso-activity curves from the semi-ideal behavior have been taken as a criterion todetermine the soluting-out/in effect occurring in the investigated systems. The VLE results generallyshowed negative deviations from the semi-ideality, indicating that there are no favorable interactionsbetween amino acids and quaternary ammonium salts in aqueous media, and aqueous solutionscomposed of these solutes undergo the soluting-out phenomenon (except for DL-alanine/S(-)-proline-TBAH aqueous ternary systems that show small positive deviation from the semi-ideality). For a givenamino acid, the magnitude of negative deviations and the strength of the soluting-out effect increasewith increasing the cation alkyl chain length (TBAB > TPAB > TMAB) and the hydrophobic characterof the anion of the quaternary ammonium salts (TBAB > TBAC > TBAH). Amino acids act as thesoluting-ou agent, and their soluting-out ability follows the order S(+)-serine > glycine > DL-alanine> S(-)-proline.

کلیدواژه ها:

Amino Acids ، Tetraalkylammonium Salts ، Isopiestic ، Soluting-Out