Interactions of amino acids in aqueous triammonium citrate solutions at different temperatures: A viscometric approach Harsh Kumar ⁎, Meenu Singla, Rajeev Jindal Department of Chemistry, Dr B R Ambedkar National Institute of Technology, Jalandhar 144 011, Punjab, India abstract article info Article history: Received 25 July 2014 Received in revised form 9 September 2014 Accepted 19 September 2014 Available online 23 September 2014 Keywords: Amino acid Triammonium citrate Jones–Dole equation Transition state treatment The viscosities, η of glycine (Gly), L-alanine (Ala), and L-valine (Val) with triammonium citrate have been mea- sured as a function of temperature at T = (288.15, 298.15, 308.15 and 318.15) K. The change in viscosity of amino acids with increase in triammonium citrate concentration and temperature is attributed to amino acid– triammonium citrate interactions. The viscosity B-coefficients and viscosity interaction parameters obtained from the Jones–Dole equation and transition state theory respectively have been discussed to interpret interac- tions between ions of amino acids and triammonium citrate. Further, enthalpy of viscous flow and entropy of vis- cous flow have been determined. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Amino acids are the low molar mass model compounds or building blocks of proteins which can be used for studies which are expected to set impacts on the solvation and conformation of proteins [1,2]. In gen- eral, the electrolytes present in our body influence the properties of bi- ological molecules like proteins which are the vital part of our body. The interactional behavior of large biomolecules like hormones, enzymes and especially proteins are difficult to understand due to many specific interactions which occur in these complex molecules. The B-coefficient values obtained from viscosity values and calculated using the Jones– Dole equation are a very good parameter to describe the kosmotropic and chaotropic nature of solute in different solvents. Much work has been done on the determination of the B-coefficient of amino acid and peptides in aqueous [3–8] and aqueous electrolyte solutions [9–13] but there has been less focus on the interactions of amino acids with the salts, which are involved in the biochemical process of the body [14,15] like citrates and phosphates. These salts are of valuable impor- tance in industries like medicines, biosensors, optics, cosmetics and play a significant role in various metabolic processes [16–18]. In continuation to our research program on thermodynamics studies [19–22] of amino acids with salts of citrates, here, the viscosities, η of glycine, L-alanine and L-valine in (0.0, 0.2, 0.4, 0.6 and 0.8) mol·kg -1 aqueous triammonium citrate solutions at T = (288.15, 298.15, 308.15 and 318.15) K have been reported. Our main aim here is to study the interactional behavior of amino acids with these salts, which will further help us in better understanding these classes of compounds. As per our knowledge, no data has been reported on viscosities of mix- ture containing amino acids and triammonium citrate so far. 2. Experimental Glycine (Gly), L-alanine (Ala), and L-valine (Val) with mass fraction purities N 0.99 procured from Merck, Germany and triammonium cit- rate with mass fraction purity N 0.99 purchased from SD Fine Chem. Ltd. India were used as supplied. However, these were vacuum dried before use and then were kept over P 2 O 5 in a desiccator for 48 h. All the aqueous solutions were prepared afresh in double distilled and degassed water having specific conductance b 10 -6 S·cm -1 . The speci- fication of the chemicals used has also been given in Table 1. All the weightings were made on a Sartorius CPA225D balance having a preci- sion of ±0.00001 g. Uncertainty in the solution concentration was esti- mated to be ±2 × 10 -5 mol·kg -1 in calculations. The AntonPaar Automated MicroViscometer (AMVn) was used to determine dynamic viscosities, η of the solutions. The temperature was controlled to ± 0.01 K by a built in Peltier thermostat. The measure- ment of viscosities with AMVn is based on the falling ball principle. A calibrated glass capillary with a steel ball as supplied by the manufactur- er with AMVn was filled with the sample to measure the ball falling time. The ball falling time and densities were used to estimate kinematic as well as dynamic viscosities. The calibration of capillary was per- formed by the manufacturer using viscosity standard fluids. The exper- imental uncertainty in viscosity measurement was estimated to be less than ± 1.5 × 10 -2 mPa·s. The densities used in the calculations have taken from our earlier reported results [22]. Journal of Molecular Liquids 199 (2014) 385–392 ⁎ Corresponding author. E-mail addresses: h.786.man@gmail.com, manchandah@nitj.ac.in (H. Kumar). http://dx.doi.org/10.1016/j.molliq.2014.09.038 0167-7322/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq