L-histidine solubility studies and thermodynamic behaviour in aqueous solutions of monovalent metal nitrates

• Solubility of L-histidine was measured at different temperatures in aqueous sodium nitrate and potassium nitrate salts. • The experimental solubility data were correlated using the van’t Hoff, modified Apelblat, and λh models. • Salting-in/salting-out effects of the electrolytes on the solubility were explained. • Thermodynamic parameters were calculated and explained for the experimental system. • Solvation of L-histidine increases in both NaNO₃ and KNO₃ solutions, with a stronger effect in KNO₃. This article deals with the equilibrium solubility and thermodynamic aspects of L-histidine in water and in aqueous NaNO 3 and KNO 3 solutions. The solubility was evaluated at different temperatures, ranging from 288.15 K to 308.15 K. The solubility data of L-histidine in pure water and aqueous NaNO₃ and KNO₃ solutions were correlated using three thermodynamic models: the van’t Hoff model, the modified Apelblat equation, and the λh equation. The salting-in effect serves as key factor for the variation of solubility in the electrolytic medium. The obtained solubility was used to estimate the thermodynamic behaviour of the solution systems . An analytical gravimetric technique was employed for the determination of solubility of L-histidine in the experimental solution system. In addition, the thermodynamic parameters, including Gibbs free energies, entropies and enthalpies were calculated using least-square method. To ensure the purity of L-histidine from the solvent systems, atomic absorption spectroscopy, IR and XRD studies were performed following standard protocols . Density functional theory (DFT) calculations were performed to support the molecular-level interpretation of ion–solute interactions. Additionally, this analysis elucidates the non-covalent interactions, covering the dissolution and dissolution firmness of amino acid, by considering short-range solute–solvent interactions.