The enthalpic interactions between eight kinds of amino acid and urea in aqueous solutions at 298.15K

The enthalpies of mixing of aqueous urea solutions and eight kinds of aqueous amino acid solutions (glycine, L - alanine, L - serine, L - proline, L - hydroxproline, L - methionine, L - threonine and L valine) have been determined at 298.15K by LKB - 2277 now microcalorimetric system. The data have been analyzed in terms of the McMillan - Mayer formalism to obtain the enthalpic virial coefficients for heterotactic interactions. The pairwise interactions between amino acids and urea have been studied by a group contribution additivity approach. The results show that the zwitterionic groups and different side - groups of the amino acids, such as non - polar alkyl groups, hydroxy group and five - membered pyrolidine ring, make their different contributions to enthalpic pair interactions.