Xingen Hu

Transfer Volumes of Glycine, L-Alanine and L-Serine in Glycerol-Water Mixtures at 25 - C

Densities of solutions of glycine, L-alanine, and L-serine have been measured by an oscillating-tube densimeter at 25°C in glycerol–water mixtures with glycerol mass fractions ranging from 0 to 0.50. Apparent molar volumes and limiting partial molar volumes of each amino acid have been calculated. The trends of transfer volumes have been interpreted by the cosphere overlap model. The results show that the presence of glycerol in water decreases the electrostriction caused by the amino acid zwitterion.

Enthalpic interactions of L-alanine and L-serine in aqueous urea solutions

The enthalpies of dilution of L-alanine and L-serine in various aqueous urea solutions have been determined by flow microcalorimetry at 298.15 K. The homogeneous enthalpic interaction coefficients over the whole range of aqueous urea solutions have been calculated according to the excess enthalpy concept. The results were interpreted from the point of view of solute‐solute interactions moderated by solvent effects. # 2000 Elsevier Science B.V. All rights reserved.

Enthalpic Interaction of Amino Acids with Ethanol in Aqueous Solutions at 25°C

The enthalpies of mixing aqueous ethanol solutions and with aqueous amino acid solutions (glycine, L-alanine, L-serine, L-threonine, and L-proline) and their respective enthalpies of dilution have been determined at 25°C by a flow microcalorimetric system. The experimental data have been analyzed in terms of McMillan-Mayer formalism to obtain the enthalpic virial coefficients for heterotactic interaction. The results have been interpreted from the point of view of solute-solute interactions.

The effects of environmental conditions on the growth of petroleum microbes by microcalorimetry

Abstract The growth and metabolism ability of two strains of petroleum microbe isolated from oil reservoirs was studied by calorimetry. Thermal power–time curves under various environmental conditions (including temperature, acidity, salinity and carbon source) were determined. Typical microbial growth thermal power–time curves were obtained. By fitting the curves mathematically with the ‘three-point method’ under an inhibitory condition, the growth rate constants and the optimum growth conditions (including temperature, acidity and salinity) of the microbes studied were obtained. Irregular thermal power–time curves were obtained when the petroleum microbe E grew in the media containing different carbon sources.

Thermodynamics of dissociation of glycine in aqueous ethanol and urea solutions

The dissociation enthalpies of glycine in aqueous ethanol and urea solutions have been determined at 298.15 K by LKB-2277 BioActivity Monitor. Combined with the corresponding Gibbs free energies, the dissociation entropies have been calculated. The results have been interpreted with the point of view of structure alteration of the two solvents.

Enthalpic and entropic contributions to substituent effects on the ionization of meta- and para-nitrobenzoic acids in EtOH–H2O mixtures at 298.15 K

Abstract Enthalpic and entropic contributions to substituent effects on the ionization of meta - and para -nitrobenzoic acids in EtOH–H 2 O mixtures have been examined in terms of ρ H , σ H and ρ S , σ S . The variations of ρ H and ρ S are attributed to the structural alteration of the mixed solvents.

Electrostatic model for substituent and solvent effects on organic acids

Abstract On the bases of experimental results from gas phase and electrostatic theory a modified thermodynamic model for substituent and solvent effects on organic acids has been derived. It is found that the present model is quantitatively and simultaneously consistent with the experimental results obtained from gas phase, aqueous solution and mixed solvents such as ethanol–H2O.