Expliciting the interactions of tramadol hydrochloride + choline chloride-based deep eutectic solvent + water systems: Thermodynamic aspects

Abstract

In recent years, a new class of environmentally friendly solvents called deep eutectic solvents (DESs) have been employed in a number of operations in both academia and industry. The study described herein offers an assessment of a green solvent in the preparation of Drug delivery systems (DDSs) as well as delivery vehicles made of a deep eutectic system (DES) constituted of Choline Chloride (ChCl) and Urea (U). For the designing of such processes, there is a need for an understanding of the molecular interaction of Tramadol hydrochloride with DES. In this regard, we have experimentally measured density and sound velocity for Tramadol hydrochloride in aqueous solutions and in different concentrations of aqueous DES (i.e., 0.25, 0.50, and 1.0)mol.kg−1 within the concentration range 0 to 0.15 mol.kg−1 at various temperatures (288.15, 298.15, 308.15 and 318.15) K. In order to interpret the view on solute–solvent and solute–solute interactions, several derived parameters chiefly apparent molar volume of solute (Vϕ), isentropic compressibility (κS), apparent molar isentropic compressibility of solute (KS,ϕ) for tramadol hydrochloride in aqueous and in an aqueous DES solutions have been calculated from experimental density and speed of sound values. The limiting apparent molar volume of solute (Vϕ0) and limiting apparent molar isentropic compressibility of solute (KS,ϕ0) for binary as well as ternary systems have been calculated from apparent molar volume and compressibility values. The thermal coefficient of expansion (α) and partial molar isobaric expansion (Eϕ0) have been derived from the temperature dependence of limiting apparent molar volume of solute. Transfer volume (ΔVϕtrans0) and transfer compressibility ΔKS,ϕtrans0 of tramadol hydrochloride from aqueous to aqueous DES solutions have been calculated.