Excess heat capacities of mixtures containing 1-methylpyrrolidin-2-one,chlorotoluenes and benzene

Excess heat capacities, ${(C_P^E)}_{\mathit{ijk}}$ of {1-methylpyrrolidin-2-one (i) + benzene (j) + o- or m- or p-chlorotoluene (k)} and $C_P^E$ of their sub-binary {1-methylpyrrolidin-2-one (i) + benzene (j)}; {benzene (i) + m- or p-chlorotoluene (j)} mixtures have been determined using their measured heat capacities data at T = (293.15, 298.15, 303.15) K and 0.1 MPa using micro differential scanning calorimeter. The results are discussed in terms of Graph (which deals with the topology of the constituent molecules) theory. The results suggest that $C_P^E$ and ${(C_P^E)}_{\mathit{ijk}}$ values commuted by Graph theory compare well with experimental values.     

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.     

Physico-chemical properties of some electrolytes in water and aqueous sodiumdodecyl sulfate solutions at different temperatures

The viscosities of some mineral salt viz.; potassium chloride, potassium nitrate, magnesium chloride, magnesium nitrate, at different concentrations have been determined in water and in binary aqueous solution of sodiumdodecyl sulfate (SDS) (0.007 mol · kg⁻¹ and 0.01 mol · kg⁻¹) at different temperatures. The data have been analyzed using Jones–Dole equation and the derivative parameters B and A have been interpreted in terms of ion–solvent and ion–ion interactions respectively. The change of Gibbs free energy of activation $(\mathrm{\Delta }{G}_{\eta }^{\ne })$, enthalpy of activation $(\mathrm{\Delta }{H}_{\eta }^{\ne })$, and entropy of activation $(\mathrm{\Delta }{S}_{\eta }^{\ne })$ for viscous flow of the solutions were calculated using Eyring equation, which depicts the mechanism of viscous flow. The structure making/breaking nature of the studied electrolytes has been discussed in the light of first derivative of B-coefficient (dB/dT) over temperatures. Potassium chloride and potassium nitrate acts as structure breaker in water where as all the salts are structure makers in aqueous SDS solutions, i.e. the postmicellar and pre-micellar regions.     

Thermodynamics of solvation of some small peptides in water at T = 298.15 K

The enthalpies of solution in water, Δ_solH_m, of some small peptides, namely the amides of five N-acetyl substituted amino acids of glycine, l-alanine, l-proline, l-valine, l-leucine and two cyclic anhydrides of glycine and l-sarcosine (diketopiperazines), were measured by isothermal calorimetry at T = (296.84, 306.89, and 316.95) K. The enthalpies of solution at infinite dilution at T = 298.15 K were derived and added to the enthalpies of sublimation, ${\mathrm{\Delta }}_{\mathrm{sub}}{H}_{\mathrm{m}}^{\circ }$, at the same temperature, to obtain the corresponding solvation enthalpies at infinite dilution, ${\mathrm{\Delta }}_{\mathrm{solv}}{H}_{\mathrm{m}}^{\infty }$. Moreover, the partial molar heat capacities at infinite dilution at T = 298.15 K, $C_{p\text{,}2}^{\infty }$, were calculated by adding molar heat capacities of solid small peptides, C_p,m(cr), to the ${\mathrm{\Delta }}_{\mathrm{sol}}{C}_{p\text{,}\mathrm{m}}^{\infty }$ values obtained from our experimental data. CH₂ group contributions, in terms of solvation enthalpy and partial molar heat capacity, were −3.2 kJ · mol⁻¹ and 89.3 J · K⁻¹ · mol⁻¹, respectively, in good agreement with the literature data. Simple additive methods were used to estimate the average molar enthalpy of solvation and partial molar heat capacity at infinite dilution for the 1/2CONH⋯CONH functional group in the small peptides. Values obtained were −46.7 kJ · mol⁻¹ for solvation enthalpy and −42.4 J · K⁻¹ · mol⁻¹ for partial molar heat capacity, significantly lower than values obtained for the CONH functional group in monofunctional model compounds.     

Volumetric and acoustic study of aqueous binary mixtures of quinine hydrochloride,guanidine hydrochloride and quinic acid at different temperatures

In the present communication, we report the fundamental thermodynamic properties like volumetric and compressibility of very important bioactive compounds, viz. quinine hydrochloride, guanidine hydrochloride and quinic acid (0.01 to 0.1) mol · kg⁻¹ in water at temperatures T = (278.15, 288.15 and 298.15) K. The experimental values of density (ρ) of aqueous solutions and speed of sound (u) in aqueous solutions of the above compounds within the concentration range (0.01 to 0.1) mol · kg⁻¹ have been obtained. The apparent molar volumes (V_ϕ), and apparent molar isentropic compressibilities (κ_ϕ) of quinine hydrochloride, guanidine hydrochloride and quinic acid in water have been computed at three different temperatures. Speed of sound values have also been used to calculate the hydration number (n_H) of the solute. The temperature dependence of the apparent molar volume has been used to calculate the thermal expansion coefficient (α¹), apparent molar expansivity $(E_{\varphi }^0)$ and Hepler’s constant $\left({\partial }^2{V}_{\varphi }^0/\partial T^2\right)$. The derived parameters have been used to interpret the results in terms of (solute + solute)/(ion + ion), (solute + solvent) interactions, structure making and structure breaking tendencies of solutes in water.