Micellization of mixtures of amphiphilic drugs and cationic surfactants: A detailed study

The micellization behaviors of two amphiphilic drugs ((amitriptyline hydrochloride (AMT) and imipramine hydrochloride (IMP)) in presence of cationic surfactants (conventional as well as gemini) have been investigated conductometrically at four mole fractions and four temperatures. The critical micelle concentration (cmc) values come out to be lower than cmcid values (cmcid is the cmc value at ideal mixing state) indicating attractive interactions between the two components in mixed micelles. Micellar mole fractions of surfactants (X1 and X1M), calculated by Rubingh and Motomura models, are always greater than X1id (micellar mole fraction at ideal mixing). The rigid structure of drugs decreases their contribution in mixed micelles as compared to that predicted by X1id values. Although α1 (mole fraction of surfactant) is higher for DTAB than that of 12-4-12, the contribution of 12-4-12 is almost equal to that of DTAB. The interaction parameter (β) is negative at all temperatures and at all compositions indicating attractive interactions. Activity coefficients (f1 and f2) are always less than unity suggesting nonideality in the systems. Thermodynamic parameters suggest dehydration of hydrophobic part of the drug at or above certain temperature which is different for the two drugs.

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► Micellization of amphiphilic drug–cationic surfactant systems have been analyzed.
► Rubingh and Motomura models show higher contribution of surfactants in mixed micelles.
► The negative β   values suggest attractive interactions between the components.
► For drug/drug–surfactant systems, ΔHm° values change from negative to positive with temperature.