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

Abstract 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, h xy , and triplet, h xxy and h xyy , interactions between hydrated solute molecules were estimated using the McMillan-Mayer formalism. Similar to the homotactic parameters h xx and h yy , the h xy 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, h xx  > 0 and h xy  > 0, a fact testifying to the prevailingly hydrophobic character of the Ala – Meb interaction in the aqueous medium.