Bijoy Krishna Dolui

Solubility of DL-serine and DL-phenylalanine in aqueous mixtures of dimethyl sulfoxide and solvation thermodynamics

The standard free energies (ΔG0t(i)) and entropies (ΔS0t(i)) of transfer of DL-serine and DL-phenylalanine from water (1) to aqueous mixtures of dimethylsulfoxide (DMSO) (2) at 298.15 K are reported in the present study. The transfer energies have been determined from solubility measurements of the amino acids. The solubility is measured at different temperatures i.e. from 288.15 to 308.15 K by an ‘analytical gravimetric method’. The chemical parts of the free energies (ΔG0t,ch(i)) and entropies (TΔS0t,ch(i)) of transfer of the amino acids have been computed by subtracting the cavity effects and dipole–dipole interaction effects from the total transfer energies. The characteristics of the solvation thermodynamics of the amino acids in an aqua-organic solvent system are studied and discussed in the present manuscript.

Thermodynamics of DL-alanine solvation in water-dimethylsulfoxide mixtures at 298.15 K

In this study we mainly discuss the transfer Gibbs free energy ΔGt0(i) and ΔSt0(i)entropy of DL-alanine at 298.15 K and consequently the involved chemical transfer free energy (ΔGt,ch0(i)) and entropy (TΔSt,ch0(i)) in aqueous mixtures of dimethylsulfoxide are discussed to clarify the solvation chemistry of DL-alanine. For the evaluation of these energy terms, solubility of this amino acid has been measured by formol titrimetry at five equidistant temperatures i.e., from 288.15 to 308.15 K in different composition of this mixed solvent system. The various solvent parameters as well as thermodynamic parameters like molar volume, density, dipole moment and solvent diameter of this solvent system have also been reported here. The chemical effects of the transfer Gibbs energies (ΔGt,ch0(i)) and entropies of transfer (TΔSt,ch0(i)) have been obtained after elimination of cavity effect and dipole-dipole interaction effects from the total transfer energies. Here the chemical contribution of transfer energetics of DL-alanine is mainly guided by the composite effects of increased dispersion interaction, basicity effect and decreased acidity, hydrogen bonding effects, hydrophilic hydration and hydrophobic hydration of aqueous DMSO mixtures as compared to that of reference solvent, water.

Physico-chemical studies of DL-alanine in aqueous sodium nitrate solution

In this study solubility of DL-alanine is measured in aqueous solutions with various NaNO3 concentrations using the “formol titrimetry” method in the temperature range from 288.15 to 308.15 K. The standard transfer Gibbs energy and entropy have been evaluated for alanine. Chemical effects of the transfer Gibbs energy [ΔGi,ch0(i)], were obtained by subtracting theoretically computed ΔGt,cav0(i) and ΔGt,d-d0(i) from the total transfer free energy, ΔGt0(i). TΔSi,ch0(i) have been evaluated after elimination of cavity and dipole-dipole interaction effects from total transfer [TΔSt0(i)] entropy. Various solvents and thermodynamic parameters are presented in this manuscript. The data accumulated demonstrated that solubility was affected by the electrolyte.

Thermodynamics and mechanisms of glycine solvation in aqueous NaCl and KCl solutions at 298.15 K

In the present study the solubility of glycine in aqueous sodium chloride and potassium chloride solution was determined under different experimental conditions using ‘formol titrimetry’ method. The thermodynamic parameters like standard transfer Gibbs energies and entropies have been evaluated at 298.15 K. Other important parameters like molar volume, densities, solvent diameter, etc., of the experimental solutions have also been determined in this study. The above mentioned parameters have been used to determine ∆t,ch0(i)i.e., chemical effects of the transfer Gibbs energies and T∆t,ch0(i)i.e., chemical effects of the transfer entropy. The solvation of glycine is influenced by different factors such as nature of the solute, interactions between solute and solvents, etc., which has been explained by different physical and analytical approach.

Thermodynamics of DL-α-aminobutyric acid induced solvation mechanism in aqueous KCl solutions at 288.15–308.15 K

The solubilities of DL-α-aminobutyric acid in KCl solutions of different concentrations are measured at 288.15–308.15 K. Gibbs energies and entropies have been determined for transfer of α-aminobutyric acid form water to aqueous KCl solution at 298.15 K. The cavity, dipole-dipole and other interactions affecting the solubility, as well as stability of the amino acid in solution are also evaluated. Gibbs energy and entropy of transfer due to interactions are computed to create the model of the complex solute-solvent and solventsolvent interactions. Molar volume, densities, dipole moment of solvent and diameter of co-solvent in aqueous potassium chloride are also evaluated.

Solvation Thermodynamics of DL-Phenylalanine in Aqueous NaNO3 Solution at 298.15 K

By “formol titrimetry” method solubilities of DL-phenylalanine (PA) in aqueous NaNO3 solution were measured at 298.15 K. The standard Gibbs energy of PA in aqueous and aqueous NaNO3 solution and also transfer free energy of PA was evaluated. The thermodynamic parameters: molar volume, densities, dipole moment and solvent diameter of aqueous solution of NaNO3 have also been reported. Electrolyte effects on the solubility and relative stability of PA is guided by different types of interactions which are explained in this manuscript.

Solvation thermodynamics of L-cystine, L-tyrosine, and L-leucine in aqueous-electrolyte media

Solubilities of L-cystine, L-tyrosine, and L-leucine in aqueous NaCl media at 298.15 K have been studied. Indispensable and related solvent parameters such as molar mass, molar volume, etc., were also determined. The results are used to evaluate the standard transfer Gibbs free energy, cavity forming enthalpy of transfer, cavity forming transfer Gibbs free energy and dipole-dipole interaction effects during the course of solvation. Various weak interactions involving solute–solvent or solvent–solvent molecules were characterized in order to find their role on the solvation of these amino acids.

The chemical stability of L-isoleucine, L-threonine, and L-serine in aqueous solutions of KCl at 298.15 K

The experimental saturated solubilities of L-isoleucine, L-threonine, and L-serine in aqueous mixtures of a KCl solution at 298.15 K are presented in this article. The solubilities are measured by gravimetric method. In the present study the theoretical calculation of the standard transfer Gibbs free energy, cavity forming enthalpy of transfer, cavity forming transfer Gibbs free energy, dipole-dipole interaction effect have been computed. The chemical effects of the transfer Gibbs energies for the present amino acids have been obtained by subtracting the cavity effects and dipole-dipole interaction effects from the ΔGt0(i). The stability of the experimental amino acids in aqueous KCl in terms of thermodynamic parameters is explained.