Association behavior of a mixed system of the antidepressant drug imipramine hydrochloride and dioctyl sulfosuccinate sodium salt: Effect of temperature and salt

Herein, we have checked the interaction between the imipramine hydrochloride (IMH, an antidepressant drug) and anionic surfactant dioctyl sulfosuccinate sodium salt (AOT) mixed system through a conductometric method in aqueous medium along with electrolyte solutions at different temperatures (288.15 to 303.15 K). Considerable changes were obtained in the different physicochemical parameters estimated in the current system. The AOT has an exceptional surface activity together with a very low critical micelle concentration (cmc) value as compared with other anionic surfactants, therefore, having much less toxicity. The deviations between observed cmc and ideal critical micelle concentration (cmcid) values point to an interaction between IMH and AOT. The value of cmc of the mixed system reduces through the increase of the mole fraction of AOT. With a rise in the temperature, the cmc value of pure IMH along with IMH-AOT mixtures increases first and then decreases with a further rise in the temperature. In the presence of 50 mmol·kg−1 NaCl, the observed cmc of the individual constituents along with IMH-AOT mixtures was clearly lower than that in an aqueous system. The micellar mole fraction values according to different proposed models X1Rub (Rubingh), X1Mot (Motomura), X1Rd (Rodenas) and X1ideal (ideal mole fraction) were estimated and the results obtained reveal the high contribution of AOT in the mixed micellization and the values increase through the rise in the mole fraction of AOT. At all studied temperatures the magnitudes of free energy of micellization (∆Gm0), interaction parameter (β) along with excess free energy (∆Gex) evaluated for the current studied system were obtained to be negative. The value of the activity coefficients (f1 and f2) were also computed by employing the method specified in the literatures. The negative values of enthalpy (ΔHm0) of the systems at lower temperature indicate the micellization is exothermic while at higher temperature negative values of ΔHm0 becomes positive, which means the micellization process becomes endothermic. The values of entropy (ΔSm0) were found to be positive in all cases. All of the estimated results imply a strong interaction among the studied constituents.