Jinsuo Lu

Viscosity behavior of some α-amino acids and their groups in water–sodium acetate mixtures

Abstract Viscosities of glycine, dl -α-alanine, dl -α-amino- n -butyric acid, dl -valine and dl -leucine have been determined in water–sodium acetate mixtures at 298.15 and 308.15 K. The viscosity B -coefficients have been calculated. The corresponding activation free energies (Δμ 2 0≠ ) for viscous flow have been evaluated with the help of the Feakins equation. The contributions of the charged end group (NH 3 + ,COO − ) and CH 2 groups of the amino acids to B -coefficient and Δμ 2 0≠ have been also determined using the linear correlation between B -coefficient or Δμ 2 0≠ and the number of carbon atoms in alkyl chains of the amino acids. The results have been interpreted in the light of the solute–solvent interactions in aqueous media.

Partial molar volumes of some α-amino acids in aqueous sodium acetate solutions at 308.15 K

Abstract The apparent molar volumes V 2,φ have been determined for glycine, dl -α-alanine, dl -α-amino-n-butyric acid, dl -valine and dl -leucine in aqueous solutions of 0.5, 1.0, 1.5 and 2.0 mol kg −1 sodium acetate by density measurements at 308.15 K. These data have been used to derive the infinite dilution apparent molar volumes V 0 2,φ for the amino acids in aqueous sodium acetate solutions and the standard volumes of transfer, Δ t V 0 , of the amino acids from water to aqueous sodium acetate solutions. It has been observed that both V 0 2,φ and Δ t V 0 vary linearly with increasing number of carbon atoms in the alkyl chain of the amino acids. These linear correlations have been utilized to estimate the contributions of the charged end groups (NH 3 + ,COO − ), CH 2 group and other alkyl chains of the amino acids to V 0 2,φ and Δ t V 0 . The results show that V 0 2,φ values for (NH 3 + ,COO − ) groups increase with sodium acetate concentration, and those for CH 2 are almost constant over the studied sodium acetate concentration range. The transfer volume increases and the hydration number of the amino acids decreases with increasing electrolyte concentrations. These facts indicate that strong interactions occur between the ions of sodium acetate and the charged centers of the amino acids. The volumetric interaction parameters of the amino acids with sodium acetate were calculated in water. The pair interaction parameters are found to be positive and decreased with increasing alkyl chain length of the amino acids, suggesting that sodium acetate has a stronger dehydration effect on amino acids which have longer hydrophobic alkyl chains. These phenomena are discussed by means of the cosphere overlap model.

MEAN ACTIVITY COEFFICIENTS OF NACL IN GLUCOSE-WATER AND SUCROSE-WATER MIXTURES AT 298.15 K

The mean activity coefficients of NaCl in aqueous solutions of 10, 20 and 30 mass% sugar (glucose and sucrose) have been determined at 298.15 K from emf measurements in the molality range 0.006–2.0 mol kg–1. The results have been analysed by using the Debye–Huckel extended equation and the Pitzer equation. There is good agreement between the results obtained from these theoretical models. It has been shown that two parameters of the Pitzer equation, β(0) and β(1), increase linearly with the increasing reciprocal of the relative permittivity for the mixed solvents as well as the mole fraction of sugar in the mixed solvents. A similar linear relationship was also found for the ion-interaction parameter, C, of the Debye–Huckel extended equation.

Standard Gibbs energies of transfer of some electrolytes from water to aqueous sucrose solutions at 298.15 K

Standard Gibbs energies of transfer, ΔtG⊖, of KCl, NaCl, MgCl2 and CaCl2 from water to aqueous solutions of 5, 10, 15, 20, 25 and 30 wt.% sucrose have been determined at 298.15 K from emf measurements of cells without liquid junctions. Data are also given for the Gibbs energies of pairwise interaction, gNE, of the electrolytes with sucrose in water. The electrolytes are increasingly destabilized in the mixed media with increasing mole fraction of sucrose. The Gibbs energies of interaction were found to be slightly negative for KCl–sucrose and positive for other pairs in water. The experimental results are discussed in terms of solute–solvent and solute–solute interactions in ternary water–sucrose–electrolyte systems.

Effect of temperature on viscosity properties of some α-amino acids in aqueous urea solutions

Abstract Viscosities for solutions of glycine, dl -α-alanine, dl -α-amino- n -butyric acid, dl -valine, dl -leucine and l -serine in 5 mol kg −1 aqueous urea have been determined at 278.15, 288.15, 298.15 and 308.15 K. The viscosity B -coefficients for the amino acids in the aqueous urea solution have been calculated at different temperatures. The effect of temperature on the B -coefficients is discussed on the basis of the Feakins equation. The contribution of solute to the activation parameters (Δ μ 2 0≠ , Δ H 2 0≠ , Δ S 2 0≠ ) for viscous flow of the solution have been calculated, together with the Gibbs energy, enthalpy and entropy of transfer for the amino acids from the ground-state solvent to the hypothetical viscous transition state solvent. The contributions of the charged end group (NH 3 + , COO − ) and CH 2 groups of the amino acids to B -coefficient and Δ μ 2 0≠ have been also estimated using the linear correlations between B -coefficient or Δ μ 2 0≠ and the number of carbon atoms in the alkyl chains of the amino acids. All the activation parameters are discussed in terms of the solutesolvent interactions in the ground and transition states.

A thermodynamic study of the ternary system water + glucose + electrolyte at 298.15 K

Abstract The standard free energies of transfer of KCl, NaCl, HC1, MgCl 2 and CaCl 2 from water to aqueous solutions of 5, 10, 15, 20, 25 and 30 Wt.% glucose have been determined at 298.15 K from e.m.f. measurements of cells without liquid junctions. It has been shown that the standard free energy of transfer for each of the electrolytes investigated increases linearly with increasing mole fraction of glucose in the mixed media. Free energies of pair interaction have also been calculated: these were found to be positive for NaCl-glucose, HCl-glucose and CaCl 2 -glucose pairs, and nearly zero for KCl-glucose and MgCl 2 -glucose pairs in water. The experimental results are discussed in terms of solute-solvent and solute-solute interactions in water + glucose + electrolyte systems.

The enthalpic interaction parameters of acetamide with sodium halides in water at 298.15 K

The enthalpies of solution have been measured for glycine in some sodium halide solutions at 298.15 K. The enthalpic interaction parameters hxy, hxxy and hxyy of glycine with the sodium halides have been evaluated. The dependences of the enthalpic interaction parameters on the ionic size of the electrolytes have been discussed with respect to electrostatic and structural interactions.

Calorimetric and volumetric studies of the interactions of formamide with alkan-1-ol in water at 298.15 K

Abstract Enthalpies of solution and apparent molar volumes have been measured for formamide in aqueous methanol, ethanol and propanol solutions by using a C-80 microcalorimeter and vibrating tube digital densimeter. According to these data, enthalpic and volumetric interaction coefficients were obtained. The pair interaction coefficients are discussed from the perspective of dipole–dipole interaction and structural interaction. At the same time, attempts have been made to interpret the triplet coefficients by using the solvent separated association pattern.

Thermodynamics of the interaction of HCl with d-arabinose in water at 278.15–318.15 K

Abstract The thermodynamic parameters of interaction of HCl with d -arabinose in water were determined from electromotive force measurements from 278.15 to 318.15 K. The standard Gibbs free energies of transfer of HCl from water to aqueous solutions of 5, 10, and 15 wt.% of d -arabinose were evaluated. The group interaction Gibbs free-energy parameters ( G HCl–CH 2 , G HCl–OH , G HCl– e -OH , G HCl– a -OH , and G HCl–O ) for the HCl–sugar (or alcohol)–water systems were evaluated and discussed in terms of the Savage–Wood group additivity principle and the stereochemistry of sugars, where –OH, – e -OH and – a -OH stand respectively for alcohol-, equatorial- and axial-hydroxyl groups. Of the five group interactions, the HCl– e -OH interaction contributes a large positive value to the pair interaction Gibbs free-energy parameters of HCl with sugars, whereas the contributions of the HCl– a -OH and HCl–O interactions are very small.

The enthalpies of solution of α-alanine in water and in some alkali metal chloride solutions at 298.15 K

Abstract The enthalpies of solution of α-alanine were measured in water and in LiCl, NaCl and KCl solutions at 298.15 K, and the enthalpic interaction parameters h xy , h xxy and xyy of α-alanine with the three salts were evaluated. The dependences of the enthalpic interaction parameters on the ionic size of the electrolyte are discussed within the concepts of electrostatic and structural interactions.