Enthalpy-related parameters of interaction of simplest α-amino acids with the pharmaceutical mebicar (N-tetramethylglycoluril) in water at 298.15 K

The enthalpies of dilution of mixed aqueous solutions of glycine (Gly, x) or l-alanine (Ala, x) with mebicar (Meb, y), a well-known pharmaceutical, were measured calorimetrically at 298.15 K. The enthalpic heterotactic coefficients for pair, hxy, and triplet, hxxy and hxyy, interactions between hydrated solute molecules were estimated using the McMillan-Mayer formalism. Similar to the homotactic parameters hxx and hyy, the hxy value for the ternary (water + Gly + Meb) system was found to be negative in sign. It points to the predomination of zwitterion (hydrophilic) - hydrophilic interactions in this mixed solution. In the case of the (water + Ala + Meb) system, hxx > 0 and hxy > 0, a fact testifying to the prevailingly hydrophobic character of the Ala - Meb interaction in the aqueous medium.