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

Standard Volumetric Properties of Chiral N-Methyl-Substituted Glycolurils in Water between 278.15 and 318.15 K at Ambient Pressure

“…Such a conclusion is confirmed by the fact that the contribution (increment) of the CH 2 group to the standard molar heat capacity of hydration, Δ solv C p,2 o , has been found to be the same (δ C p,2 o ≈ 34.2 J•mol −1 •K −1 at T = 298.15 K) too, regardless of the methylation character within a specified series: MMGU < trans-DMGU < TriMGU (< Mebicar). 6 Moreover, all the glycoluril derivatives studied (including Mebicar) dissolve in water with endothermic effect decreasing abruptly in magnitude on going from MMGU (24.0 kJ•mol −1 ) to TriMGU (5.9 kJ•mol −1 at T = 298.15 K). 6 The given fact suggests that the interaction of each of the considered chiral glycoluril derivatives with surrounding water is weaker than the interaction between the solute molecules in its own crystal phase.…”

“…It may be connected with the different ability of stereochemically distinguishable molecular forms of a glycoluril molecule to hydrogen bonding with water at the expense of proton-acceptor (C = O) groups and proton-donor (N−H and HC−CH) moieties. [6][7][8]32,37,38 One can assume that V 2 o (T) for the chiral (racemic) glycoluril derivatives being studied here, similarly to Nmethyl-substituted acyclic ureas, is influenced by the following: 7,34 (i) an intrinsic contribution from each CH 3 group, (ii) a hydrophobic contribution caused by a molecule sequential methylation, (iii) a hindrance for hydrogen bonding due to an N-methylated position, and a possible decrease in ability to form CO•••H bonds as well. According to the trend of sequential increase in V 2 o expressed by eq 3, the first two of the mentioned effects are to be perhaps most important in the case considered here.…”

“…4,5,10−12 To identify the fact that the specific rotation of each of the samples synthesized is zero, a Polamat A type polarimeter (Germany) with an angle resolution of 0.005°at D = 589 nm (the sodium spectral line) has been employed. 6 We have not found the optical activity in the racemates of MMGU and TriMGU due to mutual canceling of the specific rotation of their R-(+)-and S-(−)-enantiomeric molecules.…”

“…534.8 and 365.7 K). 6 The authenticity of crystalline MMGU and TriMGU (after synthesis) was also established with TriMGU. These are in excellent agreement with the previously published data.…”

“…These are in excellent agreement with the previously published data. 6 Water of natural isotope composition has been initially deionized and then twice distilled (in a device of glass Pyrex) up to a specific conductivity of 1.2 × 10 −6 S•cm −1 .…”