Standard formation enthalpies of L-leucine aqueous solutions
Comprehensive study of amino acids and peptides is very urgent currently. Amino acids can serve as model analogues of more complicated biological systems. Amino acids can be divided into aliphatic or aromatic ones and amino acids without polar or nonpolar functional group depending on the chemical nature of the side chains. Specific features of individual amino acid residues in the protein are due to physico-chemical properties of their hydrated condition of the side chains. The study of amino acids properties in aqueous solutions is especially important since many biochemical processes are taking place exactly in water.
L-leucine is an aliphatic amino acid containing an uncharged non-polar functional group. L-leucine participates in many biochemical reactions being an essential amino acid. L-leucine is used to treat liver diseases, anemia, etc.
The heat effects of crystalline L-leucine dissolution in water and potassium hydroxide solution were defined at 298.15 K by a direct calorimetric method. Measuring of crystalline L-leucine heat of dissolution was carried out in an isothermal calorimeter and automated temperature recorder. Calorimeter installation work was verified by the heat of crystalline potassium chloride dissolution in water. The equilibrium composition of the solutions was calculated on PC-Pentium 3 with RRSU program.
Standard enthalpies of L-leucine formation and its dissociation products in aqueous solutions were also calculated. The obtained values of the standard enthalpy of L-leucine formation and its dissociation products in aqueous solutions are key values in thermochemistry of L-leucine. These values open up opportunities of strict thermodynamic calculations of these compound solutions. It is necessary to accumulate a sufficient amount of experimental data on the heat of amino acids and peptides solutions to obtain empirical correlations relating the thermodynamic characteristics of the interaction between solute and solvent as well as the amount of soluble molecules that differ in physical and chemical nature. This would allow testing additive contribution of intermolecular interactions into different groups of molecules.
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