Jianji Wang

Apparent molar volumes and viscosity B-coefficients of some α-amino acids in aqueous solutions from 278.15 to 308.15 K

Abstract Viscosities and densities of aqueous solutions of glycine, DL -alanine, DL -α-amino- n -butyric acid, DL -valine, DL -leucine and L -serine have been measured as a function of amino acid concentration at 278.15, 288.15, 298.15 and 308.15xa0K. These data have been used to calculate the apparent molar volumes V 2, φ and viscosity B -coefficients. The calculated standard partial molar volumes V 0 2, φ and B -values were split into the contributions from the (NH 3 + ,COO − ) and CH 2 groups by linear correlations. Free energies of activation, Δ μ 0≠ 2 , of aqueous amino acids were obtained by application of the transition-state theory to the B -coefficient data, and the corresponding activation enthalpy Δ H 0≠ 2 and entropy Δ S 0≠ 2 were also given. On the basis of the contributions of (NH 3 + , COO − ) and CH 2 groups to V 0 2, φ , B -coefficient and the activation parameters, comments on the effect of amino acids and their groups on the structure of water and the relative orderness of the ground and the transition state of these solutions have been made.

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.

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 soluteue5f8solvent interactions in the ground and transition states.

VISCOSITY B-COEFFICIENTS OF SOME ALPHA -AMINO ACIDS IN AQUEOUS GUANIDINE HYDROCHLORIDE SOLUTION FROM 278.15 TO 308.15 K

The relative viscosities of glycine, DL-a-alanine, DL-a-amino-n-butyric acid, DL-valine, DL-leucine and L-serine in 6 mol kg 1 aqueous guanidine hydrochloride solution have been measured at 278.15, 288.15, 298.15 and 308.15 K. The viscosity fi-coefficients for each of the amino acids have been determined and used to probe the changes of water structure when guanidine hydrochloride is added. The corresponding activation free energies ( μ ) for viscous flow have been evaluated with the help of the Feakins equation. It has been observed that both B-coefficient and activation free energy vary linearly with increasing number of carbon atoms in the alkyl chains of the amino acids at given temperatures. These linear correlations were used to estimate the contributions of the charged end group (NHt, COO) and CH, groups of the amino acids to ñ-coefftcient and μ . Based on the data of μ for the amino acids and their groups, the contributions of (NHÍ, COO) and CH, groups to activation enthalpy ( ) and entropy (¿JS?) were also reported. The activation parameters are discussed in terms of the solutesolvent and solvent-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.

VOLUMETRIC PROPERTIES OF SOME ALPHA -AMINO ACIDS IN AQUEOUS UREA SOLUTION AT 278.15, 288.15, 298.15 AND 308.15 K

The partial molai volumes at infinite dilution, V^, for glycine, dl-a-analine, dl-«aminobutyric acid, dl-valine, dl-leucine and l-serine in 5 mol kgaqueous urea solution have been determined at 278.15, 288.15, 298.15 and 308.15 from precise density measurements. These data have been utilized, in conjunction with the data obtained for them in water, to deduce the standard volumes of transfer of the amino acids, zf , from water to 5 mol

Thermodynamics of the interaction of HCl with D-galactose in water at 278.15–318.15 K

Thermodynamic parameters of the interaction of HCl with D-galactose in water have been determined from electromotive force measurements at 10 K intervals from 278.15 to 318.15 K. Standard Gibbs energies of transfer of HCl from water to aqueous solutions of 5, 10, 15 wt.% D-galactose were evaluated. Comparison of pair interaction parameters of HCl–D-galactose was made with those of HCl–D-glucose and HCl–D-arabinose. The difference between these parameters was interpreted in terms of the stereochemistry of these monosaccharides. An enthalpy–entropy compensation has been observed with the pair interaction parameters for the HCl–sugar–water systems at each given temperature studied. The salting constants, kS, of D-galactose, D-glucose, D-fructose, D-arabinose, and sucrose by HCl in water were calculated from (a) the Debye–MacAulay theory (DMT); (b) Conway–Desnoyers–Smith theory (CDST); (c) the internal pressure theory developed by McDevit–Long (IPT); (d) the scaled particle theory (SPT). The results show that the calculated values of kS are reasonably in agreement with the experimental ones.

Thermodynamics of the interaction of HCl with propan-2-ol in water at 278.15–338.15 K

The emfs of cells Pt, H2(g, p0)| HCl(mE)| AgCl/Ag, and Pt, H2(g, p0)| HCl(mE), 2-PrOH(mN)| AgCl/Ag have been measured at 10 K intervals from 278.15 to 338.15 K, where 2-PrOH refers to propan-2-ol, mE= 0.005–0.1 mol kg–1, and mN= 0.2–0.7 mol kg–1. The emf data were used to determine the salting-out constant, ks, of 2-PrOH and the thermodynamic interaction parameters, ƒEN(gEN, hEN, sEN, cP, EN) of 2-PrOH with HCl in water at different temperatures. It has been shown that ks > 0, gEN > 0, hEN > 0, sEN > 0 and cP, EN < 0 at all temperatures concerned (except for sEN and hEN which are negative at 328.15 and 338.15 K) and that sEN and cP, EN vary linearly with increasing temperature. A comparison of these thermodynamic parameters is made with those for HCl–PG (propane-1,2-diol) and HCl–GL (glycerol) pairs in water. The dependence of the parameters on the number of hydroxy groups in alcohol molecules has been interpreted on the basis of the group additivity model.