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, 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. (C) 2018 Elsevier Ltd.