A study of the interaction between a phenothiazine drug promazine hydrochloride with cationic surfactants

A tensiometric study at 303.15 K was made to study the binary mixed systems of a phenothiazine drug promazine hydrochloride with six cationic surfactants (decyl-, dodecyl-, tetradecyl-, hexadecyltrimethylammonium bromides, and cetylpyridinium bromide/chloride). Relevant parameters were evaluated by using the Regular Solution Theory and Motomura treatment for binary mixed systems. Clint's model was also used to explain the nonideal behavior of the systems. The synergistic behavior (i.e., non-ideal behavior) for binary mixtures is explained by the deviation of critical micelle concentration (cmc) from ideal critical micelle concentration (cmc*), micellar mole fraction (X-1(m)) from ideal micellar mole fraction (X-1(ideal)), the values of interaction parameter (beta) and activity coefficients (f(i)) (for both mixed micelles and mixed monolayer). The excess free energy (Delta G(ex)) explains the stability of mixed micelles in comparison to micelles of pure drug: the stability decreases with the increase in alkyl chain length of the surfactant. Interfacial parameters, i.e., Gibbs surface excess (Gamma(max)), minimum head group area at air/water interface (A(min)), free energy of micellization (Delta G(m)(o)), and standard Gibbs energy of adsorption (Delta G(ads)(o)) were also evaluated for the systems. (C) 2013 Elsevier B.V. All rights reserved.