Intermolecular interactions of L-glutamine and L-histidine in aqueous solutions of metformin hydrochloride: Thermo-acoustic and optical properties S. Chauhan a, ⁎, K. Singh a , M.S. Chauhan a , Ahmad Umar b, ⁎⁎, C.N. Sundaresan c a Department of Chemistry, Himachal Pradesh University, Summer Hill, Shimla 171005, India b Department of Chemistry, Faculty of Science and Arts and Promising Centre for Sensors and Electronic Devices (PCSED), Najran University, P.O. Box 1988, Najran, 11001, Saudi Arabia c Department of Chemistry, Sri Sathya Sai Institute of Higher Learning, Brindavan Campus, Bangalore 560067, India abstract article info Article history: Received 16 October 2015 Received in revised form 16 November 2015 Accepted 18 November 2015 Available online xxxx The speed of sound (u)in conjunction with density (ρ) and viscosity (η) for amino acids L-glutamine and L-histi- dine in aqueous solutions of metformin hydrochloride (an anti-diabetic drug) (0.01, 0.07, and 0.13 mol·kg -1 ) have been measured in the concentration range (0.02–0.20 mol·kg -1 ) at (293.15, 298.15, 303.15, 308.15, and 313.15) K. In order to account for the consequences of drug–amino acid interactions, various acoustical parame- ters such as intermolecular free length (L f ), relative association (RA), specific acoustic impedance (Z), and molar sound number ([U]) have been evaluated from density and speed of sound data. Combined with viscosity values, the speed of sound data have been used to estimate parameters like relaxation time (τ), internal pressure (π i ), molar cohesive energy (MCE)and free volume (V f ). The results of acoustical studies are substantiated with UV– Vis studies for ternary system (water + drug + amino acid). The different kinds of intermolecular interactions existing between different components of the mixture are found to be responsible for the varying trends in afore- said different acoustic parameters. © 2015 Published by Elsevier B.V. Keywords: Metformin hydrochloride Intermolecular free length Specific acoustic impedance Molar cohesive energy UV–Vis studies 1. Introduction The drug–bio-macromolecular interaction is an important phe- nomenon in biophysical chemistry which involves a complex mech- anism [1]. The drug-action in living organisms must be regarded as vital outcome of physicochemical interactions between drug and bio-macromolecules, as it is based upon different physiological pro- cesses and nature of the receptors for drug molecules [2]. Mostly, the receptors for drug molecules are proteins whose proper functioning is decisive for an orderly life process. Moreover, the role of proteins for supporting life in relation to origin, advancement and metabo- lism of life is well-known [3]. In addition, most of the drug molecules are organic molecules having both solvophilic as well as solvophobic groups. On account of these groups, drug molecules exhibit different kinds of specific as well as non-specific interactions in their solution mixture [4]. Since most of the biochemical processes involves vol- ume change and hydration of molecules in aqueous medium, the studies on thermodynamic and transport properties of bio- molecules such as amino acids, peptides, sugars and drugs in aque- ous and aqueous additive solutions may therefore, evolve valuable information in medicinal and pharmaceutical chemistry [5]. Due to three-dimensional complex structure of proteins containing many miscellaneous functional groups, the study of mode of drug action is rather difficult; therefore for better understanding of drug–protein interactions, one of the useful approaches is to study simpler model compounds such as amino acids or small peptides which are elemen- tary units of proteins [6,7]. Metformin hydrochloride (Mfm-HCl) (Fig.1) is a biguanide, anti- diabetic or anti-hyperglycemic agent that helps to lower both basal and post-prandial elevated blood glucose in patients with type-II di- abetes [8–10]. Metformin hydrochloride controls glucose metabo- lism by decreasing hepatic glucose production and its absorption in the intestine. It increases peripheral glucose which helps in the improvement for insulin sensitivity and does not cause hyperinsulinemia [11]. Moreover, Mfm-HCl is also used for the treat- ment of polycystic ovary syndrome and is only anti-diabetic drug Journal of Molecular Liquids xxx (2015) xxx–xxx ⁎ Correspondence to: S. Chauhan, Department of Chemistry, Himachal Pradesh University, Summer Hill, Shimla– 171005, India. ⁎⁎ Correspondence to: Ahmad Umar, Department of Chemistry, Faculty of Science and Arts and Promising Centre for Sensors and Electronic Devices (PCSED), Najran University, P.O. Box 1988, Najran, 11001, Saudi Arabia. E-mail addresses: scschauhsan19@gmail.com (S. Chauhan), ahmadumar786@gmail.com (A. Umar). MOLLIQ-05245; No of Pages 10 http://dx.doi.org/10.1016/j.molliq.2015.11.035 0167-7322/© 2015 Published by Elsevier B.V. Contents lists available at ScienceDirect Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq Please cite this article as: S. Chauhan, et al., Intermolecular interactions of l-glutamine and l-histidine in aqueous solutions of metformin hydrochloride: Thermo-acoustic and op..., J. Mol. Liq. (2015), http://dx.doi.org/10.1016/j.molliq.2015.11.035