Interaction between amphiphilic antidepressant drug nortryptyline hydrochloride and conventional cationic surfactants: A physicochemical study

The interaction of cationic surfactants, namely dodecyltrimethyl ammonium bromide (DTAB) and cetrimide (CET) with tricyclic antidepressant drug, nortryptyline hydrochloride (NH) (used for depression related illness, nocturnal enuresis, chronic fatigue syndrome, irritable bowel syndrome, chronic pain or neuralgia, and migraine) were studied employing conductometric and tensiometric techniques. From these techniques, various micellar and interfacial parameters such as critical micelle concentration, cmc, micellar mole fraction, X1, micellar interaction parameter, β, activity coefficients ƒ1 and ƒ2 in the mixed micelles, excess Gibbs free energy of micellization, ΔGex0, standard Gibbs free energy, ΔGm0, surface excess concentration, Гmax, minimum surface area per molecule, Amin, and standard Gibbs free energy of adsorption ΔGad0 at the interface were evaluated. In addition to this, various other parameters such as, packing parameters of amphiphiles in the micelles, P, volume contribution of the hydrophobic chain, v, and its effective length, lC have also been calculated for pure and mixed systems. From packing parameters it was confirmed that the micelle/mixed micelles formed have spherical geometry. The ΔGm0 and ΔGad0 values for all studied systems were found to be negative and this shows that both micellization as well as adsorption processes are energetically favorable. Furthermore, the values of ΔGad0 were more negative than their corresponding ΔGm0, showing that work is done in transferring the amphiphilic monomers from interface to the micellar stage across the aqueous solution to form micelles. The interaction parameters, β, calculated by using regular solution theory were also observed to be negative suggesting synergistic interaction for the proposed mixed systems.