Partial molar volumes of organic solutes in water. XX. Glycine(aq) and l-alanine(aq) at temperatures (298 to 443) K and at pressures up to 30 MPa

Density data for dilute aqueous solutions of two amino acids (glycine, l-alanine) obtained using a flow vibrating-tube densimeter are presented together with partial molar volumes at infinite dilution (standard molar volumes, $V_{\text{m,}2}^{°}$) calculated from the measured data. The experiments were performed at temperatures from (298 up to 443) K at pressures close to the saturation line of water, at pressures in the range from (15 to 17) MPa, and at 30 MPa. Values of an analogue of isothermal compressibility, ${\kappa }_{T\text{,}2}^{°}=-(1/V_{\text{m,}2}^{°})(?V_{\text{m,}2}^{°}/?p{)}_T$, are also evaluated. Maxima on the curves $V_{\text{m,}2}^{°}(T)$ and ${\kappa }_{T\text{,}2}^{°}(T)$ are observed and discussed. The new data along with literature values of standard molar volumes and heat capacities are used for generating the recommended parameterization of an equation of state for standard molar thermodynamic properties of the aqueous amino acids.     

A thermodynamic study of ketoreductase-catalyzed reactions 4. Reduction of 2-substituted cyclohexanones in n-hexane

The equilibrium constants K for the ketoreductase-catalyzed reduction reactions (2-substituted cyclohexanone + 2-propanol = cis- and trans-2-substituted cyclohexanol + acetone) have been measured in n-hexane as solvent. The 2-substituted cyclohexanones included in this study are: 2-methylcyclohexanone, 2-phenylcyclohexanone, and 2-benzylcyclohexanone. The equilibrium constants K for the reactions with 2-methylcyclohexanone were measured over the range T = 288.15 to 308.05 K. The thermodynamic quantities at T = 298.15 K are: K = (2.13 ± 0.06); ${\mathrm{\Delta }}_{\text{r}}{G}_{\text{m}}^{\circ }=-(1.87\pm 0.06)\text{kJ}·{\text{mol}}^{-1}$; ${\mathrm{\Delta }}_{\text{r}}{H}_{\text{m}}^{\circ }=-(6.56\pm 2.68)\text{kJ}·{\text{mol}}^{-1}$; and ${\mathrm{\Delta }}_{\text{r}}{S}_{\text{m}}^{\circ }=-(15.7\pm 9.2)\text{J}·{\text{K}}^{-1}·{\text{mol}}^{-1}$ for the reaction involving cis-2-methylcyclohexanol, and K = (10.7 ± 0.2); ${\mathrm{\Delta }}_{\text{r}}{G}_{\text{m}}^{\circ }=-(5.87\pm 0.04)\text{kJ}·{\text{mol}}^{-1}$; ${\mathrm{\Delta }}_{\text{r}}{H}_{\text{m}}^{\circ }=-(2.54\pm 1.8)\text{kJ}·{\text{mol}}^{-1}$; and ${\mathrm{\Delta }}_{\text{r}}{S}_{\text{m}}^{\circ }=(11.2\pm 6.4)\text{J}·{\text{K}}^{-1}·{\text{mol}}^{-1}$ for the reaction involving trans-2-methylcyclohexanol. The standard molar Gibbs free energy changes ${\mathrm{\Delta }}_{\text{r}}{G}_{\text{m}}^{\circ }$ for the reactions (trans-2-substituted cyclohexanol = cis-2-substituted cyclohexanol) in n-hexane have also been calculated and compared with the literature data that pertain to reactions in the gas phase and at higher temperatures. Experiments carried out with a chiral column demonstrated that the enzymatic reduction of 2-phenylcyclohexanone catalyzed by the ketoreductase used in this study is not stereoselective.