Solubility and solvation energetics of L-histidine in aqueous NaCl/KCl electrolyte media

This article describes the solubility etiquette of an important amino acid L-histidine in chloro aqueous solutions of alkali metals (Na, K) under equilibrium saturated conditions through an analytical gravimetric technique at equidistant temperatures. Different thermodynamic parameters along with transfer Gibbs energies under standard conditions were estimated using theoretical methods and experimental solubilities. The way of surrounding by solvent molecules of solute L-histidine in the used media is discussed based on different modes of interactions occurring during solvation. The experimental section describes that the L-histidine solubility enhances in an aqueous KCl solution rather than in NaCl solution. The drop down in L-histidine solubility with moving up electrolyte concentrations at a certain temperature is caused by the salting-out effect. For the studied amino acid, the salting out effect is more pronounced in NaCl electrolyte at any temperature. Amino acid shows higher solubility with rising temperature in both electrolytes' solutions. The current study suggests that the physical properties of NaCl and KCl and the size of the L-histidine molecules are two crucial factors for the chemical stability of the protein building unit.