The limiting partial molar volume and transfer partial molar volume of glycylglycine in aqueous sodium halide solutions at 298.15 K and 308.15 K

Apparent volumes V_Φ of glycylglycine in aqueous NaX (X = F⁻, Cl⁻, and Br⁻) solutions have been obtained from densities of their solutions at 298.15 K and 308.15 K measured by using a precise vibrating-tube digital densimeter. These values have been utilized in conjunction with the values in water to deduce partial molar volumes of transfer ${\mathrm{\Delta }}_{\mathrm{trs}}{V}_{\mathrm{\Phi }}^{\circ }$ from water to different aqueous NaX solutions. ${\mathrm{\Delta }}_{\mathrm{trs}}{V}_{\mathrm{\Phi }}^{\circ }$ values are positive. The interpretation is that these results arise from the dominant interaction of the NaX with the charged centers of glycylglycine. The results show that ${\mathrm{\Delta }}_{\mathrm{trs}}{V}_{\mathrm{\Phi }}^{\circ }$ depend less on the temperature. Hydration numbers and interaction coefficients have been calculated from $V_{\mathrm{\Phi }}^{\circ }$ and ${\mathrm{\Delta }}_{\mathrm{trs}}{V}_{\mathrm{\Phi }}^{\circ }$ values and the values have been interpreted in terms of various interactions.     

Interactions in (l-phenylalanine/l-histidine + 0.01 mol · kg−1 aqueous β-cyclodextrin) systems at T = (293.15, 298.15, 303.15 and 308.15) K

Densities (ρ) and speeds of sound (u) have been measured for (l-phenylalanine + 0.01 mol · kg⁻¹ aqueous β-cyclodextrin) and (l-histidine + 0.01 mol · kg⁻¹ aqueous β-cyclodextrin) systems at T = (293.15, 298.15, 303.15 and 308.15) K using the density and sound velocity Meter DSA 5000 M. The ρ and u values have been utilized to evaluate values of the partial molar volume (${\varphi }_v^{\circ }$), transfer partial molar volume (${\mathrm{\Delta }}_{\text{tr}}{\varphi }_v^{\circ }$), partial molar isentropic compressibility (${\varphi }_k^{\circ }$), and transfer partial molar isentropic compressibility (${\mathrm{\Delta }}_{\text{tr}}{\varphi }_k^{\circ }$) of the systems studied. The experimentally measured and calculated parameters have been interpreted in terms of host-guest and ion-hydrophilic interactions operative in the systems.