Effect of N-acetylglycine on volumetric and acoustic behaviour of aqueous tetrabutylammonium iodide solutions at different temperatures Suresh Kumar Sharma a,⇑ , Gurpreet Singh a,c , Harsh Kumar b , Ramesh Kataria c a Department of Chemistry, D. A. V. College, Abohar 152116, India b Department of Chemistry, Dr. B. R. Ambedkar National Institute of Technology, Jalandhar 144011, India c Department of Chemistry, Panjab University, Chandigarh 160014, India article info Article history: Received 30 October 2015 Received in revised form 23 December 2015 Accepted 26 December 2015 Available online 4 January 2016 Keywords: Apparent molar volume Density Ultrasonic speed N-acetylglycine Tetrabutylammonium iodide Solute–solvent interactions abstract In this work, the experimental densities and ultrasonic speeds of N-acetylglycine in (0.01, 0.02, 0.03 and 0.04) molÁkg À1 aqueous tetrabutylammonium iodide (TBAI) solutions have been reported at tempera- tures (288.15, 293.15, 298.15, 303.15 and 308.15) K and at pressures 101 kPa. The different parameters such as apparent molar volume, limiting apparent molar volume, transfer volume, partial molar expansibility have been derived from density data. Experimental values of ultrasonic speeds were used to estimate coefficient of isentropic compression, apparent molar isentropic compression, limiting apparent molar isentropic compression and its transfer value. The pair and triplet interaction coefficients have also been calculated from transfer parameters. All these parameters offer a convenient method to study the intermolecular interactions between the various components of the ternary mixtures. The interactions increase with increase in the concentration of N-acetylglycine in aqueous TBAI solutions. The variation of these parameters with concentration and temperature clearly suggests the role of ðC 4 H 9 Þ 4 N þ on the solute–solvent interactions in aqueous medium. Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction Salt solutions have large effects on the structure and properties of proteins including their solubility, denaturation, dissociation into subunits, and the activity of enzymes [1–3]. Proteins are com- plex molecules, and their behaviour in solutions is governed by a combination of many specific interactions. One approach that reduces the degree of complexity and requires less complex measurement techniques is to study the interactions in systems containing smaller biomolecules such amino acids and peptides. Importance of studying the smaller biomolecules having low molecular weight lies in the fact that one can systematically alter the structure and therefore contribution of side chain groups of amino acid and peptide can be seen easily. It would be interesting to see the chances in the group contributions of limiting partial molar volume upon transferring the side chains from the a-amino acids to other amino acid derivatives e.g. N-acetylamino acids. The N-acetylamino acids constitute a class of compounds in which the electrostriction effect would not be present to perturb the partial molar volume contribution of the peptide or alkyl groups. In proteins or polypeptides the majority of the alkyl side chains are situated in the environment of dipolar —CONH groups. Thus, the partial molar volume contribution of alkyl side chains in the N-acetylamino acids may represent a value close to that in polypeptides or proteins. Some studies [4,5] have revealed that the presence of an elec- trolyte drastically affects the behaviour of amino acids in solutions, and this fact can be used for their separation and purification. Ther- modynamic properties of amino acids in aqueous electrolyte solu- tions thus provide valuable information about solute–solvent and solute–solute interactions. Hence there has been a number of works [6–14] revealing the effect of electrolyte solutions on amino acids. Salts such as tetraalkylammonium halides can give a better insight into the effect of electrostatic and hydrophobic interactions on the stability of proteins as these salts are known to influence macromolecular conformations by weakening attraction or repul- sion of inter and intra charge-transfer interactions and by affecting hydrophobic interactions through the side chain of the alkyl groups. Tetraalkylammonium salts are bulky in nature and are known to orientate water molecules around them depending on their alkyl chain [15,16]. They do not interact electrostatically with water molecules being hydrophobic in nature. In order to avoid http://dx.doi.org/10.1016/j.jct.2015.12.023 0021-9614/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: suresh30091978@gmail.com (S.K. Sharma). J. Chem. Thermodynamics 96 (2016) 143–152 Contents lists available at ScienceDirect J. Chem. Thermodynamics journal homepage: www.elsevier.com/locate/jct