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

Abstract

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