Hydration numbers of glycine in an aqueous urea solution

Abstract

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.

Hydration numbers of α-alanine in an aqueous urea solution

“…It was shown [2] that this is also true for glycine. **The study [2] derived a linear dependence 0 V (W) for glycine. ***The solution density is an important parameter that is necessary for various calculations.…”

“…The calculated results from equation (5) [2]. We assume that the V h value in aqueous urea solutions is the same as in water.…”

“…***The solution density is an important parameter that is necessary for various calculations. Considering (2) and (4), the following equation can be written for the apparent volume of α-alanine in an aqueous urea solution: φ = 60.50 + 0.0766W + 0.65m A . This equation allows us to find the density of the ternary system: water-urea-α-alanine.…”

“…The purpose of this study is to analyze the data on apparent volumes of α-alanine in water and aqueous urea solutions, obtain an analytical expression for the dependence of the partial volume of alanine on the urea concentration, and calculate the hydration numbers of alanine. This paper continues the study of hydration numbers of substances in aqueous urea solutions [1,2].It should be mentioned that the properties and structure of aqueous urea solutions continue to be in focus of researchers [3][4][5][6][7][8][9]. Urea is most often referred to as a destroyer of water structure, but there are other points of view (see [10,11] and references therein).…”

“…The purpose of this study is to analyze the data on apparent volumes of α-alanine in water and aqueous urea solutions, obtain an analytical expression for the dependence of the partial volume of alanine on the urea concentration, and calculate the hydration numbers of alanine. This paper continues the study of hydration numbers of substances in aqueous urea solutions [1,2].…”