Interaction Between an Active Pharmaceutical Ingredient Ionic Liquid Benzalkonium Salicylate and Small Biomolecules in Aqueous Solution: UV Absorption, Conductivity, and Volumetric Study

Abstract

UV absorption spectroscopy, electrical conductivity and density experiments have been used to investigate the interactions of some small biomolecules (amino acids/dipeptides) with an active pharmaceutical ingredient in ionic liquid form (API-IL), benzalkonium salicylate (BaSal), in aqueous solution. A number of useful parameters, such as critical micellar concentration (cmc), aggregation number (Nagg) and limiting molar conductivity (Λ0) of BaSal, standard partial molar volumes (\(V_{2,\phi }^{ \circ }\)), corresponding volumes of transfer from water to aqueous BaSal solutions (ΔtrVo), standard partial molar expansibilities (\(E_{\phi }^{ \circ }\)), hydration number (nH) of small biomolecules, as well as the binding constants (Kb) for small biomolecule–BaSal complexes have been evaluated. The dependence of the properties on concentration, temperature and alkyl chain length of amino acids/dipeptides is examined. The results are used to identify the solute–solvent physicochemical interactions occurring in the studied systems.