Experimental and theoretical approach to cationic drug-anionic gemini surfactant systems in aqueous medium

Herein the results of surface tension measurements on the mixed systems of an amphiphilic drug amitriptyline hydrochloride (AMT) and three anionic bisphosphodiester gemini surfactants having different hydrophobic tails (8, 10, and 12 carbon) are presented. The ex-perimental and ideal critical micelle concentration (cmc and crac(id)) values suggest synergism in mixed systems of AMT and 8-2-8/10-2-10 and attractive interaction in AMT-12-2-12 systems. Other parameters evaluated from the data also suggest mixed micellization among the components with almost 50% contribution of surfactants (micellar mole fraction, X-1(m), close to 0.5). The X-1 values evaluated from Rubingh's model (X-1(m)) and Motomura's model (X-1(m)) as well as X-m(id) values increase with increasing content of surfactants in solution. Adsorption behavior too indicates that the mixed monolayers experience attractive interaction (beta(sigma)) which vary in the order: AMT-12-2-12 < AMT-8-2-8 < AMT-10-2-10. Interaction in mixed micelles (beta(m)) follows the same trend. The results suggest that mixed systems of AMT-10-2-10 are the most stable one. Probably the difference in length of hydrophobic parts of AMT and gemini is most compatible in this system. (C) 2013 Elsevier B.V. All rights reserved.