Effect of Asymmetric Dimeric Zwitterionic Surfactants on Micellization Behavior of Amphiphilic Drugs

Abstract

The micellization process in mixtures of amphiphilic drugs and asymmetric dimeric zwitterionic surfactants have been investigated tensiometrically. The drugs used are from two families: imipramine hydrochloride (IMP)—a tricyclic antidepressant and ibuprofen (IBF)—a nonsteroidal antiinflammatory drug, whereas zwitterionic dimeric surfactants are heterogemini surfactants that contain quaternary ammonium and phosphate groups as heads. The results show that the cmc of drug-surfactant mixtures decreases with the increase in stoichiometric mole fraction of surfactants (α ₁), suggesting attractive interaction among the two components. This is supported by the values of cmc _id (critical micelle concentration values for ideal mixing) which are always greater than experimental cmc values. Also, the decrease in magnitude is more in IBF–dimeric surfactant mixed systems than in IMP–dimeric surfactant mixed systems. Micellar mole fraction values, obtained using Rubingh’s ($X_{\text{1}}^{\text{m}}$) and Motomura’s ($X_{\text{1}}^{\text{m}}$) models, are lower than the micellar mole fraction for ideal mixing ($X_{\text{1}}^{{\text{id}}}$). The micellar interaction parameter ($\beta^{\text{m}}$) follows the order: 8(−)−2−16(+) > 10(−)−2−16(+) > 10(−)−2−14(+) > 8(−)−2−14(+). The results are explained on the basis of difference in tail lengths. Interfacial mole fraction ($X_{\text{1}}^{\upsigma}$) values, evaluated using Rosen’s model, are higher than $X_{\text{1}}^{\text{m}}$ values for IMP-10(−)−2−16(+) and IMP-10(−)−2−14(+) systems while for all other systems (except 8(−)−2−14(+)) the values are smaller than $X_{\text{1}}^{\text{m}}$. The interaction parameter at the interface ($\beta^{\upsigma}$) is negative and $\beta_{av}^{\text{m}}$ values are greater than $\beta_{av}^{\upsigma}$ in magnitude. All the results indicate that the dimeric surfactants are mostly in cationic form.