Interaction of the Amphiphilic Drug Amitriptyline Hydrochloride with Gemini and Conventional Surfactants: A Physicochemical Approach

Pyrene fluorescence measurements were carried out on various binary mixtures of the antidepressant amphiphilic drug amitriptyline hydrochloride (AMT) with conventional (TTAB and CTAB) and gemini surfactants (14-4-14 and 16-4-16). In all cases mixed micellar aggregates were formed and the mixed critical micelle concentration (cmc) of various mixtures was computed from the I (1)/I (3) versus total surfactant concentration plots. In the region where mixed micelles are formed, the interaction of the amphiphlic drug and four surfactants showed synergistic behavior. The results were analyzed using an interaction parameter, beta, which characterize the interaction in the mixed micelle and is introduced by a regular solution theory. The beta values are negative in all binary mixtures, and their magnitudes increase with increasing hydrophobicity of the amphiphile. The micellar mole fraction of AMT in the mixed micelle (x (1)) and in the ideal sate (x (ideal)) were evaluated and their values (x (1) > x (ideal)) suggest that the contribution of the AMT component is greater in binary mixtures as compared to that in the ideal state. Activity coefficients (f (1) and f (2)) and excess Gibbs energy (G (ex)) were also calculated. The values of micelle aggregation numbers (N (agg)) and various other parameters like the Stern-Volmer constant (K (sv)), micropolarity and dielectric constant of mixed systems have also been evaluated from the ratios of respective peak intensities (I (1)/I (3) or I (0)/I (1)).