We have studied the temperature and length scale dependence of the energetics of the pair interaction of well-established hydrophobic solutes tetraalkylammonium bromides with hydrophilic formamide (FA) and hydrophobic hexamethylphosphoric triamide (HMPT). Our results do indicate the anomalous length scale dependence of the tetraalkylammonium cation-amide interaction in water. As the cation size is increased, the unfavorable enthalpy of interaction is increased rather linearly until the maximum is reached, after which there appears to be a reversal of the trend. We believe that this phenomenon arises from the impossibility of water to maintain its H-bond network near large tetraalkylammonium cations that leads to the formation of a somewhat disordered solute hydration shell. The energetic cost for overlapping this shell with the amide hydration shell in water is noticeably smaller than that for tetraalkylammonium cations of a moderated size.

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An analysis of the literature data on the partial molar volume of glycine in an aqueous urea solution at 298 K is performed. The mentioned value linearly increases with the increase in the urea concentration (wt.%). The hydration number of glycine decreases by a factor of 2 when passing from water to the saturated (20m) urea solution.Partial molar volumes contain information on structural changes occurring when substances of different nature are dissolved in water and parameters of the system state are altered. Within the available approaches, they enable the calculation of a structurally significant characteristic such as the hydration number. Standard partial molar volumes 0 V of glycine in an aqueous solution at the urea concentration m up to 13 mol/kg water were obtained in [1-6]*. It can be definitely stated that in the studied concentration range, 0 V increases with the increase in the concentration of the non-aqueous component. However, the data obtained by different authors are not consistent in some cases. Thus, for the 6m solution 0 V = 45.57±0.04 cm 3 /mol [2] and 45.15±0.12 cm 3 /mol [5]. The partial glycine volume (45.89±0.09 cm 3 /mol), obtained in [5] for 11m urea solution, is smaller than 0 V of glycine in the 8m solution (46.08 cm 3 /mol [3]). Here it should be taken into account that when passing from water to the 13m urea solution, 0 V of glycine increases only by 3.5 cm 3 /mol.The purpose of this work was to clarify the reasons for these discrepancies, to obtain consistent characteristics, to find an analytical expression for the dependence of glycine 0 V on the urea concentration, and to calculate the hydration numbers of the amino acid up to the saturated solution.The standard volumes are obtained by the extrapolation of the apparent volumes φ to zero amino acid concentrationwhere φ 0 = 0 ; V m A is the molality of glycine (usually m A < 1 mol/kg solvent).Consistent values of the coefficient В for glycine in water range from 0.86 to 0.97 [5,[7][8][9][10][11]. In [12], thorough determinations of φ of glycine in water, including very diluted solutions, are performed. Based on the data [12] for *Temperature here and further is standard 298.15 K.