Interaction of a Surface-Active Ionic Liquid with an Antidepressant Drug: Micellization and Spectroscopic Studies

The interaction of the antidepressant drug nortriptyline hydrochloride (NOT) with the surface-active ionic liquid (SAIL), 1-decyl-3-methylimidazolium chloride, C₁₀mim]Cl], has been studied using multiple techniques, including conductometric titration, tensiometric, fluorometric, dynamic light scattering and UV–visible spectrophotometric measurements. There is a significant decrease in the cmc of SAIL on the addition of the drug NOT, indicating adsorption of drug molecules in the outer portion of the micelle. In the present study, the values of the packing parameter, P, lie in the range of 0–0.3, which suggests that the micelles formed are spherical in nature. More negative values of the standard Gibbs energy of adsorption, \( \Delta G_{\text{ad}}^{ \circ } \), compared to \( \Delta G_{\text{m}}^{ \circ } \) support our contention that adsorption of SAIL on the air-solution interface is relatively more favorable than its micellization in the presence of NOT. Fluorescence and DLS studies indicate that the aggregation number, N_agg, and hydrodynamic radius of SAIL increase with increase in concentration of NOT. The UV–visible spectroscopic study confirms the formation of a new complex between SAIL and NOT; this is also supported by the negative Gibbs energy of complexation.