Energetics and temperature dependent behaviour of amitriptyline hydrochloride with conventional surfactant in aqueous medium

Abstract

The use of surfactants for improved solubilization of hydrophobic drugs is of great pharmacological significant. This study investigates the interaction of a nitrogen-based surfactant, cetyltrimethylammonium bromide (CTABr) with varied concentrations of a tricyclic antidepressant drug, amitriptyline hydrochloride (AHCl), at different temperatures, 298.1 – 318.1 K with a view to determine the energetics of the system. The critical micelle concentration for the system (C^SYS) occurred far below that for CTABr at 6.65x10⁻⁴ − 9.01x10⁻⁴moldm⁻³, indicating a favourable interaction. In addition, the change in Gibbs free energy ΔG_SYS (kJmol⁻¹) of the system was both temperature and concentration dependent and varied from - 7.71 to -51.479. The results of enthalpy (ΔH_SYS) and entropy ΔS_SYS) of the system showed that the system was exothermic and entropy driven on the overall. The change in molar heat capacity (ΔsysC_P) for the system was also found to be negative and the micellization process of CTABr-AHCl was enthalpy-entropy compensated with the value of compensation temperature (T_c) of 325.65 K.The micelle-lipophilic drug system was found to be thermodynamic spontaneous and feasible at the investigated temperatures and concentrations.