Interaction between antidepressant drug and anionic surfactant in low concentration range in aqueous/salt/urea solution: A conductometric and fluorometric study Malik Abdul Rub a,b, ⁎, Naved Azum a,b , Abdullah M. Asiri a,b , Sulaiman Y.M. Alfaifi a , Salman S. Alharthi c 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 c Chemistry Department, Faculty of Science, Taif University, Taif 21944, Saudi Arabia abstract article info Article history: Received 25 September 2016 Received in revised form 24 November 2016 Accepted 27 November 2016 Available online 30 November 2016 Aqueous/salt/urea micellar solutions of amphiphilic antidepressant drug amitriptyline hydrochloride (AMT) and anionic surfactant sodium dodecylbenzenesulfonate (SDBS) have been examined by conductivity and fluores- cence measurements at different temperatures and composition. From the conductometric study, values of crit- ical micelle concentration (cmc) of drug have been evaluated and analyzed in terms of effect of surfactant on the hydrophobic nature of AMT–SDBS complex. The values of critical micelle concentration (cmc) and other aggrega- tion parameters, micellar mole fraction (X 1 ) and interaction parameters (β) were obtained and discussed in de- tail. In mixtures of AMT and SDBS, the synergistic interactions in mixed micelles formation increases with the raise in mole fraction of surfactant in absence and attendance of salt/urea. Thermodynamic parameters of the mixtures in aqueous as well as in salt/urea solution have been evaluated by means of a pseudo-phase model. The effect of NaCl shows the salting-out effect, which promotes aggregate formation of AMT and SDBS as well as their mixed systems at lower concentration relative to aqueous solution. The micelle aggregation number (N agg ) of drug increases with the raise in surfactant mole fraction in mixtures. N agg value of individual and mixed amphiphiles rises in the presence of electrolyte while reduces in the occurrence of urea. © 2016 Elsevier B.V. All rights reserved. Keywords: Antidepressant drug Interaction parameter Surfactant Enthalpy Aggregation number 1. Introduction The mixtures of amphiphiles are well accounted in the literature, being of key significance with the intention of advance their aggregation and convenient applications [1–3]. Surfactants are comprehensively employed in our on a daily basis life along with also in a range of indus- trial progressions for example textiles, paints, oil, pharmaceuticals etc. [4,6]. In the mixture of amphiphiles if one of the constituent is an am- phiphilic drug in that case the mixture decreases the side effects and en- hances the drug's effectiveness [5,6]. The amphiphilic drugs such as phenothiazine and benzodiazepine tranquillizers, analgesics, non-ste- roidal anti-inflammatory and tricyclic antidepressants have strong ten- dency to self-associate like surfactants [7–9]. Among these drugs, tricyclic antidepressants (TCA's) have been keystones of antidepressive therapy for over three decades. The selected TCA's such as amitriptyline hydrochloride (AMT) are the most widely used tricyclic antidepressants in the mental health care (Scheme 1). AMT consist of a rigid hydrophobic ring as well as an alkylamine portion which turns out to be protonated at low pHs and deprotonated at elevated pHs. Employing of TCAs is one of the ap- proaches for the cure of mental disorder. On the other hand, TCAs have facing many unwanted side effects such as anticholinergic, cardio- vascular and antihistamine effects [10]. Other than this, TCAs provoke phospholipidosis, that is to say, the unnecessary intracellular gathering of phospholipids [11]. Cationic amine group of AMT interact with the anionic group of phosphate oxygen of the lipids reduces the amphiphilic nature of lipids and may change the physicochemical properties of the lipids obtain in the body. To decrease these unwanted effects, TCAs are usually employed with carriers such as surfactant. Surfactants form micelles, principally in aqueous/nonaqueous solu- tions, by means of hydrophobic and hydrophilic interactions takes place inside the similar molecule [12–15]. In the present study we have used anionic surfactant sodium dodecylbenzenesulfonate (SDBS). SDBS have several uses like, it perform as an appropriate template for the preparation of nanoparticles, bio-friendly because it desorbs a lot of dangerous organic materials from soil and advances the effectiveness of soil [16,17]. This surfactant is kind, fewer irritating to skin and also have antimicrobial property, so they will improve the access of drugs through skin. Therefore, the examination of interfacial properties of this surfactant and their interactions with bio-active materials such as drugs, proteins, enzymes, amino acids and polymers are highly signifi- cant to study to enhance their utilizes in industries. Journal of Molecular Liquids 227 (2017) 1–14 ⁎ Corresponding author at: Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia. E-mail addresses: malikrub@gmail.com, aabdalrab@kau.edu.sa (M.A. Rub). http://dx.doi.org/10.1016/j.molliq.2016.11.113 0167-7322/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq