Data on the apparent and standard partial molar volumes, Vø,2 and V¯2o(≡V¯ϕ,2∞), as well as the standard partial molar expansibilities, E¯p,2o, of N,N-dimethylglycoluril-N’-aminoisobutyric acid (DMGU-AIBA) in water were derived from density measurements of the corresponding aqueous solutions between 278.15 and 318.15 K and at ambient pressure. The uncertainty in density experiments did not exceed 0.10 kg m–3, and the solution molality for the aqueous DMGU-AIBA ranged from 0.002 to 0.06 mol·kg–1. Using the previously obtained results, it was established that the N’-alkyl-chain isomerization of N,N-dimethylglycoluril-aminobutyric acid (DMGU-ABA) as a solute in water, to form DMGU-AIBA, leads to squeezing of the structure packing of the formed “hydration complex”. This effect, being increasingly pronounced with rising temperature, is supposed to be due to a change in the solute–solvent interaction balance, against the background of an increase in the effect of solvent electrostriction near the solute molecule. It was concluded that the decisive role in the hydration of amino acid glycoluril derivatives belongs to hydrophilic effects, associated mainly with heterocomponent interactions through proton-donating/-accepting pharmacophore moieties, despite partial dissociation of DMGU-AIBA and DMGU-ABA in the aqueous medium.
Ivanov et al. (Tue,) studied this question.