Peculiarities of electrostatic interactions between amino acids and salicylic acid in aqueous solution

Based on calorimetric data, the enthalpy of transfer of salicylic acid to aqueous buffer solutions with the addition of different amino acids at the constant acidity of medium pH 7.35 was determined. It was shown that the exothermicity of transfer and negative enthalpic coefficients for these pairwise interactions of salicylic acid with amino acids considerably increase with increasing charge of amino acid existing in the ionic form under these conditions. Weak interactions of salicylic acid with the anionic form of aspartic and glutamic acids are related to the repulsion between anion carboxyl groups. More intense interactions are observed for zwitterions of glycine and alanine. The most intense specific interactions with salicylic acid are observed for lysine and arginine, which exist in the solution as cations.