Thermochemical properties of l-α-amino acids in electrolyte–water mixtures

Dissolution enthalpies of l-α-alanine, dl-α-alanine, l-α-aminobutyric acid, l-α-valine, l-α-leucine, l-α-seryne and l-α-threonine in mixtures of water with NaCl, KCl and LiCl have been measured by calorimetry at 298.15 K. The enthalpic heterogeneuos interaction coefficients of the amino acid zwitterion with the electrolyte have been determined using the standard solution enthalpies of amino acid in water and in aqueous solution of electrolytes. The values of the resultant enthalpic pair interaction coefficients are interpreted assuming a criterion in the form of the effect of hydrophobic alkyl radicals of amino acids side chains on the interactions between the polar head of the amino acid and the dissociated electrolyte.