A study of interaction between antidepressant drug nortriptyline hydrochloride with gelatin

The effect of gelatin on the micellization behavior of amphiphilic drug nortriptyline hydrochloride (NOT) in aqueous as well as aqueous urea (250 mM) solutions has been studied using conductimetric technique. NOT is indicated for the relief of symptoms of depression. It is a tricyclic antidepressant drug. The drug interacts with gelatin similar to the interaction of surfactants and polymers. The plots of specific conductivity versus concentration of drug were nonlinear with three different linear regions with two clear breaks. The first break point, i.e., critical aggregation concentration (cac), appeared well below the typical critical micelle concentration (cmc). The second break point is considered as polymer saturation point (psp) that is similar to cmc. The cac value decreases on increasing the gelatin concentration, whereas psp value increases for all fixed concentrations (%, w/v) of gelatin which is a clear signal of the interaction of the drug with gelatin. Free energies of aggregation (ΔGagg) and micellization (ΔGmic) were also evaluated. In the presence of urea the increase in the surface charge of the micelles was observed followed by halt of the aggregation. Effect of NOT (drug) on the secondary structure of gelatin in aqueous solutions was also examined using CD measurements. The measurements verified that the random coil content of gelatin increases with increasing the NOT concentration.