| Summary: | Levocetirizine dihydrochloride (LCTZ) is a second-generation antihistamine known for its efficacy without sedation. However, the binding mechanism with plasma protein which makes it devoid of sedative effects is yet to be uncovered. In this study, we elucidated thermodynamic parameters of solute-solvent and solute-cosolute interactions between LCTZ, and the amino acids l-alanine (Ala) and l-glutamine (Gln) in aqueous solutions. The volumetric and conductance parameters were calculated using the experimental density and conductance data of aqueous solutions of Ala and Gln (concentration range of 0.02–0.20 mol kg−1) and LCTZ (concentration range of 0.01, 0.07, and 0.13 mol kg−1) at 298.15, 303.15, 308.15, and 313.15 K. Volumetric analysis study revealed that the apparent molar volume (Vφ), limiting apparent molar volume (Vφ0), and Masson's coefficient (Sv) values indicated predominantly solute-solvent interactions that were influenced by the solute's concentration and temperature. Meanwhile, partial molar expansibilities (Eφ0), transfer volume ΔtrVφ0 and Hepler's constant (δ2V0/δT2) established the solution system's structure-breaking tendency. The Gibb's free energy (ΔG0) values derived from conductometry data indicated the system's spontaneity. These calculated constants provided a detailed understanding of the different types of intermolecular interactions found in the ternary (LCTZ + water + amino acids) system.
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