Enthalpies and heat capacities of solution of racemic N-methyl-substituted glycolurils in water at T = (278.15 to 313.15) K

•Enthalpies of solution of N-methylated chiral glycolurils in water were measured.•Calorimetric experiments were performed at T = (278 to 318) K and p = 99.6 kPa.•Standard molar heat capacities of solution of glycolurils in water were computed.•A solute dissolution becomes more endothermic with decreasing its hydrophobicity.•A solution heat capacity increases in proportion to number of methyl-substituents.

The molar enthalpies of solution of racemic (with enantiomer ratio of 1:1) 2-monomethyl-, 2,6-dimethyl-, and 2,4,6-trimethylglycolurils (2-MMGU, 2,6-DMGU and 2,4,6-TMGU, respectively) in water were measured calorimetrically in the temperature range between (278.15 and 313.15) K and at p = 99.6 kPa. Derived from experimental data, the standard (at infinite dilution) molar enthalpic characteristics of the dissolution process are positive by sign and increase with rising temperature as well as in a sequence of 2,4,6-TMGU < 2,6-DMGU < 2-MMGU. In the same way, the standard heat capacity of solution decreases distinctly, leading to the conclusion that the effect of hydrophobic hydration is more pronounced for the more N-methylated solute. It was suggested that, despite the presence of hydrophobic moieties (N-sited methyl groups) in the molecules considered, a hydrophilic constituent (via H-bonding) seems to be the predominant one in the total enthalpy effect of a solute hydration.

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