Equilibrium Composition Of Solutions Research Articles

STANDARD FORMATION ENTHALPIES OF HYDROXYETHYLIDENEDIPHOSPHONIC ACID AND PRODUCTS OF ITS DISSOCIATION IN AQUEOUS SOLUTION

This study aimed the measuring the standard enthalpies of formation of hydroxyethylidenediphosphonic acid and the products of its dissociation in aqueous solutions at 298.15 K. In the literature there is a large amount of data on the constants of stepwise dissociation of the acid. The works were done at different temperatures and the values of the ionic strength of the solution on the background of the different nature of the supporting electrolytes. In order to compare the values of the constants of stepwise dissociation of the acid, obtained by different authors, we recalculated the values of рK1, рK2, рK3, рК4, рК5 at zero ionic strength by the Davies equation. The most probable values of thermodynamic constants of dissociation of hydroxyethylidenediphosphonic acid were the following: рК10 = 1.7±0.03; рК20 = 2.47±0.05; рК30 = 7.78±0.05; рК40 = 10.29±0.05 and pK50 = 11.13±0.05. Calorimetric measurements were performed on an ampoule calorimeter equipped with an isothermal shell and a KMT-14 thermistor temperature sensor, and the automatic recording the temperature changes over time. The operation of installation was verified with the integral enthalpies of dissolution in water of crystalline potassium chloride and was considered suitable for measurements, if certain it ∆solН298.15 (KCl ∞ H2O)=17.234± 0.018 kJ/mol, corresponding to the standard SRM 1655NBS. The heat value of the calorimeter water was 87±12 Дж/mol virtually coincided with the thermal value of the calorimeter for potassium hydroxide. The volume of the calorimetric liquid was 43.12 ml. The hydroxyethylidenediphosphonic acid samples were weighed on a VLR-200 balance with 2∙10-4 g accuracy. The confidence range of the average ΔН value was determined at 0.95 probability. The equilibrium compositions of solutions were calculated using RRSU software. The standard enthalpies of formation of hydroxyethylidenediphosphonic acid and the products of its dissociation in aqueous solutions were calculated.Forcitation:Lytkin A.I., Chernikov V.V., Krutova O.N., Skvortsov I.A. Standard formation enthalpies of hydroxyethylidenediphosphonic acid and products of its dissociation in aqueous solution. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 4-5. P. 37-42

STANDARD FORMATION ENTHALPIES OF L-ARGININE AND PRODUCTS OF ITS DISSOCIATION IN AQUEOUS SOLUTION

Depending on the chemical nature of side radicals, amino acids can be divided into aromatic and aliphatic ones, as well as amino acids that have non-polar or polar functional groups in their side radical. Since specific features of individual amino acids in the protein are determined by the nature (physicochemical properties) of their side radicals that exist in the hydrated state, it also seems extremely important to study the thermodynamic characteristics of hydration of side radicals of amino acids of different chemical nature. In order to obtain empirical correlations that would establish a relationship between the thermodynamic parameters of interaction of a dissolved compound with the solvent and the size of molecules being dissolved (that have different physicochemical nature), one needs to accumulate a sufficient amount of experimental data on heats of dissolution of amino acids and peptides. This would allow one to verify the addictively of contributions of intermolecular interactions for different groups of molecules. Reagent L-arginine was used without additional purification. Prior to weighing, the substance was dried at 110 °C. The heats of dissolution of crystalline L-arginine were measured using an isothermal-jacket calorimeter with automatic recording of the temperature-time curve. The performance of the calorimetric setup was verified in accordance with the conventional calorimetric standards: the heat of dissolution of crystalline potassium chloride in water and the heat of neutralization of a strong acid with a strong base. The agreement between the experimental enthalpies of dissolution of KCl (cr.) in water and the heats of neutralization of nitric acid with a KOH solution with the most reliable published data indicates that there are no evident systematic errors in the performance of the calorimetric setup. The equilibrium compositions of solutions were calculated using RRSU software. The heats of dissolution of crystalline amino acid in water and potassium hydroxide solutions at 298.15 K were measured by direct calorimetry. The standard enthalpies of formation of L-arginine and the products of its dissociation in aqueous solutions were calculated.Forcitation:Lytkin A.I., Chernikov V.V., Krutova O.N., Krutov P.D. Standard formation enthalpies of L-arginine and products of its dissociation in aqueous solution. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 2. P. 40-45