Interaction between Zwitterionic Surfactants and Amphiphilic Drug: A Tensiometric Study

Abstract

Abstract The physicochemical properties, viz, critical micelle concentration (cmc), surface excess concentration (Γ max), minimum area per head group (A min) of zwitterionic surfactants (designated as n(−)-2-m(+); n = 8, 10, 12 and m = 12, 14, 16) and their mixtures with amphiphilic antidepressant drug amitriptyline hydrochloride (AMT) were determined by using surface tension measurements. The cmc and ideal cmc (cmcid) values along with interaction parameters, β m and β σ (calculated using Rubingh's and Rosen's models), suggest attractive interactions among the components. The Krafft temperature measurements also indicate strong attractive interactions. Γ max (or A min) increases (or decreases) with the addition of gemini surfactant; the values being closer to that of the drug. These values and micellar mole fraction (X1 m-calculated from Rubingh's model and X 1 Moto-calculated from Motomura's model) indicate larger contribution of gemini surfactants in mixed micelles and smaller contribution at air/solution interface (as mole fraction values at interface, X 1 σ , are slightly smaller than X 1 m). The standard Gibbs energy of micellization (Δ G micº) and adsorption (Δ G adº) as well as excess energy of mixing (Δ G ex m) are all negative. All these results suggest higher stability of the mixed systems. UV absorbance results also suggest that the mixed micelles are stable for several days.