Solubility and Chemical Thermodynamics of d,l-Alanine and d,l-Serine in Aqueous NaCl and KCl Solutions

Abstract

The solubilities of D,L-alanine and D,L-serine in aqueous sodium chloride (NaCl) and potassium chloride (KCl) solutions are determined at five equidistant temperatures by using "formol titrimetry". The thermodynamic parameters such as standard transfer Gibbs energies, entropies, and enthalpies have been evaluated at 298.15 K. Other important related parameters like molar mass, density, molar volume, dipole moment, and solvent diameter, etc., of the experimental solutions are also determined in the present study. ΔG t,ch 0 (i), i.e., chemical effects of the transfer Gibbs energies, and TΔS t,ch 0 (i), i.e., chemical effects of the transfer entropy of these amino acids, are also evaluated and discussed, the factors which are dependent on mainly nature of the solute, solvent, interactions between solute and solvent, etc. The nature and the extent of the involved factors, which are influencing the solvation of the amino acids in aqueous NaCl and KCl solutions, are also explained by the different physical and analytical approaches.

Solubility and Thermodynamics of Solute–Solvent Interactions of Some Amino Acids in Aqueous Sodium Bromide and Potassium Bromide Solutions

“… where, S R and S S are solubilities of amino acids in aqueous media in the absence and presence of salt, respectively. In the mole fraction scale the standard transfer free energies (Δ G t 0 ( i )) were determined using eq . , where M S and M R are the molar masses of electrolytes (NaBr/KBr) and H 2 O (reference solvent), respectively. In this case uncertainty of molar mass ( M S ) was found as ±0.0003 (Tables and ).…”

“…The determined values of Δ G t 0 ( i ) are shown in Tables and . Considering dipole–induced dipole factor to be infinitesimally small − one may ascribe Δ G t 0 ( i ) as the summation of various free energy terms; − where Δ G t,cav 0 ( i ) represents transfer free energy due to cavity formation which involves the creation of cavities by experimental molecule in aqueous media in the absence and presence of salts. Δ G t,d–d 0 ( i ) represents the free energy due to dipole–dipole interaction as a result of interaction between zwitter-ionic amino acid molecule and solvent water molecule.…”

“…In designing the mode of separation of amino acids, the precise determination of the solubility behavior in experimental mixtures of this class of molecules is indispensable. As amino acids are the basic building blocks of proteins, advancement of knowledge on thermodynamic behaviors of these molecules in aqueous media have been introduced as an active area of research for quite long time. − The solubility of this type of molecules in water and different water-electrolyte solutions and the solvation of these molecules in terms of thermodynamic parameters are imperative in the purification and solution chemistry of proteins. − These studies are also important in chemical, food, and pharmaceutical industries. − Because of the presence of −NH 2 and −COOH groups in amino acids, these molecules exist in aqueous media as zwitterions at pH 7. The zwitterions are polar having a significant dipole moment, which results in several weak interactions involving this dipole.…”

Solubility analysis of homologous series of amino acids and solvation energetics in aqueous potassium sulfate solution

“…For quite a long time a significant attention has been made to study the thermodynamics of biologically important small molecules such as amino acids in dilute aqueous electrolyte solutions. It provides valuable information about the nature of the interactions between polar and nonpolar groups, water and aqueous electrolytes and thus contributes in understanding the chemistry of protein like complex systems in aqueous medium [1, 2, 3, 4, 5, 6]. In this case the solubility data are necessary to explain the thermodynamics and useful in the clarification of solute–solute and solute–solvent interactions [7, 8].…”

“…The aim of the present work is to find out the effect of hydrophobic alkyl group and the influence of ionic –NH 2 and –COOH groups on the solubility of the experimental amino acids in the presence of electrolyte. On the other hand the amino acids have been used extensively as model compound for more complex biomolecules such as proteins, but a more thoughtful understanding of the electrolyte effect on amino acid solutions is still desirable to reveal the molecular interactions between salts and protein functional groups [1, 2, 3, 4, 5, 6]. From the theoretical point of view the interactions between electrolyte ions and small molecules with biological macromolecules are of substantial importance in determining the nature of macromolecules.…”