Research paper Solubility and transfer solvation thermodynamics of L-isoleucine and L-serine in water to aqueous solution of Na 2 SO 4 and K 2 SO 4 from 288.15 K to 303.15 K Saroj Chowdhury a , Prasenjit Mandal a , Md. Sarikul Islam a , Aslam Hossain b , Partha Sarathi Guin c , Sanjay Roy c,⇑ , Kalachand Mahali a,⇑ a Department of Chemistry, University of Kalyani, Nadia, Kalyani, India b Department of Physical and Inorganic Chemistry, Institute of Natural Sciences and Mathematics, Ural Federal University, 620000 Yekaterinburg, Russia c Department of Chemistry, Shibpur Dinobundhoo Institution (College), Howrah 711102, West Bengal, India article info Article history: Received 24 May 2018 In final form 15 June 2018 Available online 20 June 2018 Keywords: L-Isoleucine L-Serine Sodium sulfate Potassium sulfate Aqueous solution Thermodynamic parameters abstract The solubilities of L-isoleucine and L-serine in aqueous sodium sulfate (Na 2 SO 4 ) and potassium sulfate (K 2 SO 4 ) from 298.15 to 308.15 K are presented. The solubilities are measured by ‘gravimetric’ method. The relative solubility of the amino acids is calculated to explain the salting-in and salting-out effect in the electrolytes solutions. The amino acids solvation thermodynamical parameters are computed. The chemical effects of the transfer Gibbs energies for both the amino acids are estimated by subtracting the cavity effect and dipole-dipole interaction effect from the total transfer energies. The chemical trans- fer energetics is employed to discuss solute-solvent and solvent-solvent interactions. Ó 2018 Elsevier B.V. All rights reserved. 1. Introduction Amino acids are the building units of proteins which play the most important biochemical functions in human physiology. Twenty percent of the human body is made up of protein. A large section of our cells, muscles and tissues are fabricated from amino acids which means that they carry out many functions, such as providing cells their structure [1]. They play a crucial role in the transport and storage of various nutrients. Amino acids influence the function of many organs, glands, tendons and arteries. They are also essential for healing injuries, repairing tissues and remov- ing waste deposits produced during the course of metabolism [2]. They are extensively applied in several chemicals, pharmaceuti- cals, cosmetics, food industries and biodegradable plastics [3]. The solubility of amino acids and the thermodynamic parameters related to their solvation predominantly determine their biological roles of action [4]. This is the reason why studies on solubility of amino acids in different polar and nonpolar solvents under different experimental conditions are very imperative till now. In many cases thermodynamic parameters for solvation were found to be helpful in characterizing the conformational changes of bio-macromolecules like proteins in solution in the presence of electrolytes [6–10]. Though in many studies effect of size, shape, charge, hydrogen bonding capability, hydrophobicity, hydrophilic- ity, zwitterionic character, chemical reactivity, etc., on the solubil- ities of amino acids have been studied [11,12,15,16], however, still a lot of such studies remain to be done for various amino acids in various solvent systems under various experimental conditions. Amino acid molecules in the free state are rarely found in nature and they are usually obtained by the hydrolysis of protein containing materials or by fermentation. These methods involve specific inorganic salts at different concentrations, specific temper- ature and pH of the reaction media [9–10]. So it is very imperative to investigate the effect of salts on the solubility of amino acids at different temperature. In many earlier studies attempts had been made to determine the solubility and explore the solvation mech- anisms of various amino acids in pure aqueous [3,12,13,14], aqueous-organic [15,16], non-aqueous [4,6,7], and aqueous- electrolyte systems [5,9,10,13]. In the present article efforts were made to find the effect of Na 2 SO 4 and K 2 SO 4 on the solubility of L- serine and DL- isoleucine in aqueous solutions by analytical gravimetric method [3,17–20] at 288.15, 293.15, 298.15, 303.15 and 308.15 K. The relative solubility with respect to water was evaluated and applied to find thermodynamic parameters related to solvation. The study will be https://doi.org/10.1016/j.cplett.2018.06.032 0009-2614/Ó 2018 Elsevier B.V. All rights reserved. ⇑ Corresponding authors. E-mail addresses: sanjayroyp@gmail.com (S. Roy), gourkala@gmail.com (K. Mahali). Chemical Physics Letters 706 (2018) 432–439 Contents lists available at ScienceDirect Chemical Physics Letters journal homepage: www.elsevier.com/locate/cplett