1007 ISSN 1990-7931, Russian Journal of Physical Chemistry B, 2016, Vol. 10, No. 6, pp. 1007–1013. © Pleiades Publishing, Ltd., 2016. Self-Association Behavior of an Amphiphilic Drug Nortriptyline Hydrochloride under the Influence of Inorganic Salts 1 Malik Abdul Rub a, b, *, Naved Azum a, b , and Abdullah M. Asiri a, b a Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah-21589, Saudi Arabia b Center of Excellence for Advanced Materials Research, King Abdulaziz University, Jeddah-21589, Saudi Arabia *e-mail: malikrub@gmail.com Received January 15, 2016 Abstract– Herein, the micellization phenomena of an amphiphilic antidepressant drug nortriptyline hydro- chloride (NOT) have been studied using tensiometric technique in the absence and presence of different con- centration of inorganic salts (NaCl, NaBr and KCl) at 298.15 K. NOT is employed for the relief of symptoms of depression. In presence of inorganic salt the CMC value decreases which is explained on the basis of nature and ion size. Various parameters, i.e., the maximum surface excess concentration at the air/solution interface (Γ max ), minimum area per head group at the air/solution interface (A min ), free energy of micellization ( ), minimum energy of surface (G min ) and standard Gibbs energy of adsorption ( ) were evaluated and dis- cussed in detail. Keywords: antidepressant drug, surface tension, critical micelle concentration (CMC), inorganic salt, ther- modynamic parameters DOI: 10.1134/S1990793116060257 Δ o m G Δ o ads G 1. INTRODUCTION One of the most characteristic properties of the amphiphilic molecules likes drugs, surfactants, poly- mers, etc. is their ability to aggregate in solution [1–6]. When amphiphiles are dissolved in water, they initially minimize their free energy by creating a monolayer on the air-water surface. As the amphiphile concentra- tion is increased, the surface becomes increasingly populated by amphiphilc molecules, therefore decreasing the surface tension of the solution. On fur- ther addition, beyond a critical concentration (when the surface is fully occupied), they start to aggregate leading them into a variety of structures are called micelles in which the hydrophilic head groups expose towards aqueous phase and hydrophobic tails away from it that is termed critical micelle concentration (CMC) [1–6]. The well-known solution conditions like pH, ionic strength, type of additives, temperature, etc. that strongly affect the self-association phenom- ena [4, 7, 8]. Antidepressants drugs like nortriptyline hydro- chloride (NOT) are amphiphilic in nature and self aggregate in aqueous environment to form micelles (Fig. 1). The characterization of these drugs in aque- 1 The article is published in the original. ous medium has been the subject of interest due to their unusual association characteristics that derive from their rigid three-ring structure [4]. These drugs have a basic chemical structure of tricyclic hydropho- bic part and an alkylamine side chain. Depending upon the solution pH these drug molecules attained cationic or neutral form [9]. It has been established that such drugs form aggregates of around 6– 12 monomers in aqueous solutions [10, 11]. NOT is employed to take care of mental/mood problems for example depression and this drug also have side effects and requires a carrier for its secure delivery. The amphiphiles solution properties are sensitive to the attendance of additives [12, 13]. The CMC values CHEMICAL PHYSICS OF BIOLOGICAL PROCESSES Fig. 1. The molecular structure of nortriptyline hydro- chloride (NOT). H N H 3 C HCl