Three–step method to determine the eutectic composition of binary and ternary mixtures

A three-step method to determine the eutectic composition of a binary or ternary mixture is introduced. The method consists in creating a temperature–composition diagram, validating the predicted eutectic composition via differential scanning calorimetry and subsequent T-History measurements. To test the three-step method, we use two novel eutectic phase change materials based on \(\mathrm{Zn}(\hbox {NO}_3)_2\cdot 6\mathrm{H}_{2}{\mathrm O}\) and \(\mathrm{NH}_4\mathrm{NO}_3\)   respectively \(\mathrm{Mn}(\hbox {NO}_3)_2\cdot 6\mathrm{H}_{2}{\hbox {O}}\) and \(\mathrm{NH}_4\mathrm{NO}_3\) with equilibrium liquidus temperatures of 12.4 and 3.9  \(\,^{\circ }\mathrm {C}\) respectively with corresponding melting enthalpies of 135 J \(\mathrm{g}^{-1}\) (237 J \(\mathrm{cm}^{-3}\) ) respectively 133 J \(\mathrm{g}^{-1}\) (225 J \(\mathrm{cm}^{-3}\) ). We find eutectic compositions of 75/25 mass% for \(\mathrm{Zn}(\hbox {NO}_3)_2\cdot \mathrm{6H}_{2}{\mathrm{O}}\) and \(\mathrm{NH}_4\mathrm{NO}_3\) and 73/27 mass% for \(\mathrm{Mn}(\hbox {NO}_3)_2\cdot 6\mathrm{H}_{2}{\mathrm{O}}\) and \(\mathrm{NH}_4\mathrm{NO}_3\) . Considering a temperature range of 15 K around the phase change, a maximum storage capacity of about 172 J \(\mathrm{g}^{-1}\) (302 J \(\mathrm{cm}^{-3}\) ) respectively 162 J \(\mathrm{g}^{-1}\) (274 J \(\mathrm{cm}^{-3}\) ) was determined for \(\mathrm{Zn}(\hbox {NO}_3)_2\cdot \mathrm{6H}_{2}{\mathrm{O}}\) and \(\mathrm{NH}_4\mathrm{NO}_3\) respectively \(\mathrm{Mn}(\hbox {NO}_3)_2\cdot \mathrm{6H}_{2}{\mathrm{O}}\) and \(\mathrm{NH}_4\mathrm{NO}_3\) .     

Ion-molecular interactions in solutions of potassium and cadmium thiocyanates in N-methylpyrrolidone at 298.15 k, according to calorimetry and densitometry data

The heat capacity and density of KNCS-N-methylpyrrolidone (MP), Cd(NCS)₂-MP, and KNCS-Cd(NCS)₂-MP solutions at 298.15 K are studied by means of calorimetry and densitometry. Standard partial molar heat capacities and volumes ( $\bar C^\circ _{p,2} $ and $\bar V^\circ _2 $ ) of the studied electrolytes in MP are calculated. Standard values of heat capacity $\bar C^\circ _{p,i} $ and volume $\bar V^\circ _i $ of NCS^? ions in MP at 298.15 K are determined. Values of the heat capacity and volume changes upon the formation of the three-component system KNCS-Cd(NCS)₂-MP from binary solutions are obtained and discussed.     

Thermodynamic study of metal corrosion and inhibitor adsorption processes in copper/N-1-naphthylethylenediamine dihydrochloride monomethanolate/nitric acid system: part 2

N-1-Naphthylethylenediamine dihydrochloride monomethanolate (N-NEDHME) was tested as a corrosion inhibitor for copper in 2 M HNO₃ solution using the standard gravimetric technique at 303–343 K. N-NEDHME acts as an inhibitor for copper in an acidic medium. Inhibition efficiency increases with increase in concentration of N-NEDHME but decreases with a rise in temperature. Thermodynamic parameters such as adsorption heat ( $ \Updelta H_{\text{ads}}^\circ $ ), adsorption entropy ( $ \Updelta S_{\text{ads}}^\circ $ ) and adsorption free energy ( $ \Updelta G_{\text{ads}}^\circ $ ) were obtained from experimental data of the temperature studies of the inhibition process at five temperatures ranging from 303 to 343 K. Kinetic parameters activation such as $ E_{a} $ , $ \Updelta H_{\text{a}}^\circ $ , $ \Updelta S_{\text{a}}^\circ $ and pre-exponential factors have been calculated and are discussed. Adsorption of N-NEDHME on the copper surface in 2 M HNO₃ follows the Langmuir isotherm model.     

Volumetric and Viscometric Studies in Binary Liquid Mixtures of 2-Methyl-2-propanol with Some Ketones at Different Temperatures

Densities, ??, and viscosities, ??, of binary mixtures of 2-methyl-2-propanol with acetone (AC), ethyl methyl ketone (EMK) and acetophenone (AP), including those of the pure liquids, were measured over the entire composition range at 298.15, 303.15 and 308.15?K. From these experimental data, the excess molar volume $V_{\mathrm{m}}^{\mathrm{E}}$ , deviation in viscosity ????, partial and apparent molar volumes ( $\overline{V}_{\mathrm{m},1}^{\,\circ }$ , $\overline{V}_{\mathrm{m},2}^{\,\circ }$ , $\overline{V}_{\phi ,1}^{\,\circ}$ and $\overline{V}_{\phi,2}^{\,\circ} $ ), and their excess values ( $\overline{V}_{\mathrm{m},1}^{\,\circ \mathrm{E}}$ , $\overline{V}_{\mathrm{m,2}}^{\,\circ \mathrm{ E}}$ , $\overline {V}_{\phi \mathrm{,1}}^{\,\circ \mathrm{ E}}$ and $\overline{V}_{\phi \mathrm{,2}}^{\,\circ \mathrm{ E}}$ ) of the components at infinite dilution were calculated. The interaction between the component molecules follows the order of AP > AC > EMK.     

Chemical Transfer Energies of Some Homologous Amino Acids and the –CH2– Group in Aqueous DMF: Solvent Effect on Hydrophobic Hydration and Three Dimensional Solvent Structure

Standard transfer Gibbs energies, $ \Updelta_{\text{tr}} G^{^\circ } $ , of a series of homologues α-amino acids have been evaluated by determining the solubility of glycine, alanine, amino butyric acid and norvaline gravimetrically at 298.15 K. Standard entropies of transfer, $ \Updelta_{\text{tr}} S^{^\circ } $ , of the amino acids have also been evaluated by extending the solubility measurement to five equidistant temperatures ranging from 288.15 to 308.15 K. The chemical contributions $ \Updelta_{\text{tr,ch}} G^{^\circ } (i) $ of α-amino acids, as obtained by subtracting theoretically computed contributions to $ \Updelta_{\text{tr}} G^{ \circ } $ due to cavity and dipole–dipole interaction effects from the corresponding experimental $ \Updelta_{\text{tr}} G^{ \circ } $ , are indicative of the superimposed effect of increased basicity and dispersion and decreased hydrophobic hydration (hbh) in DMF–water solvent mixtures as compared to those in water, while, in addition, $ T\Updelta_{\text{tr,ch}} S^{^\circ } (i) $ is guided by structural effects. The computed chemical transfer energies of the –CH₂– group, $ \Updelta_{\text{tr,ch}} P^{^\circ } $ (–CH₂–) [P = G or S] as obtained by subtracting the value of lower homologue from that of immediately higher homologue, are found to change with composition indicating involvement of several opposing factors in the calculation of the chemical interactions. The $ \Updelta_{\text{tr,ch}} G^{^\circ } $ (–CH₂–) values are found to be guided by the decreased hydrophobic effect in DMF–water mixtures, and are indicative of the nature of the three dimensional structure of the aquo-organic solvent system around each solute.     

Thermodynamic investigations of 1-ethyl-3-methylimidazolium tetrafluoroborate and cycloalkanone mixtures

The densities, ρ, speeds of sound, u, and heat capacities, (C _P)_mix, for binary 1-ethyl-3-methylimidazolium tetrafluoroborate (1) + cyclopentanone or cyclohexanone (2) mixtures within temperature range (293.15–308.15 K) and excess molar enthalpies, H ^E, at 298.15 K have been measured over the entire composition range. The excess molar volumes, V ^E, excess isentropic compressibilities, \( \kappa_{\text{S}}^{\text{E}}, \) and excess heat capacities, \( C_{\text{P}}^{\text{E}}, \) have been computed from the experimental results. The V ^E, \( \kappa_{\text{S}}^{\text{E}} \) , H ^E, and \( C_{\text{P}}^{\text{E}} \) values have been calculated and compared with calculated values from Graph theory. It has been observed that V ^E, \( \kappa_{\text{S}}^{\text{E}} \) , H ^E, and \( C_{\text{P}}^{\text{E}} \) values were predicted by Graph theory compare well with their experimental values. The V ^E, \( \kappa_{\text{S}}^{\text{E}}, \) and H ^E thermodynamic properties have also been analyzed in terms of Prigogine–Flory–Patterson theory.     

Lamellar/Disorder Phase Transition in a Mixture of Water/2,6-Dimethylpyridine/Antagonistic Salt

The effects of adding an antagonistic salt, sodium tetraphenylborate ( \(\hbox {NaBPh}_4\) ), to a binary mixture of deuterated water and 2,6-dimethylpyridine were investigated by visual inspection, optical microscopy, and small-angle neutron scattering. With increasing salt concentration, the two-phase region shrinks. When the concentration of \(\hbox {NaBPh}_4\) is \(85\hbox { mmol}{\cdot} \hbox {L}^{-1}\) , a temperature-induced lamellar/disorder phase transition is observed at 338 K. These trends are similar to those observed for a mixture of water/3-methylpyridine/ \(\hbox {NaBPh}_4\) (Sadakane et al., Phys. Rev. Lett. 103, 167803 (2009)).     

Densities,Refractive Indices,Ultrasonic Speeds and Excess Properties of Acetonitrile + Poly(ethylene glycol) Binary Mixtures at Temperatures from 298.15 to 313.15 K

The densities, ρ, refractive indices, n _D, and ultrasonic speeds, u, of binary mixtures of acetonitrile (AN) with poly(ethylene glycol) 200 (PEG200), poly(ethylene glycol) 300 (PEG300) and poly(ethylene glycol) 400 (PEG400) were measured over the entire composition range at temperatures (298.15, 303.15, 308.15 and 313.15) K and at atmospheric pressure. From the experimental data, the excess molar volumes, \( V_{\text{m}}^{\text{E}} \) , deviations in refractive indices, \( \Delta n_{\text{D}} \) , excess molar isentropic compressibility, \( K_{{s , {\text{m}}}}^{\text{E}} \) , excess intermolecular free length, \( L_{\text{f}}^{\text{E}} \) , and excess acoustic impedance, Z ^E, have been evaluated. The partial molar volumes, \( \overline{V}_{\text{m,1}} \) and \( \overline{V}_{\text{m,2}} \) , partial molar isentropic compressibilities, \( \overline{K}_{{s , {\text{m,1}}}} \) and \( \overline{K}_{{s , {\text{m,2}}}} \) , and their excess values over whole composition range and at infinite dilution have also been calculated. The variations of these properties with composition and temperature are discussed in terms of intermolecular interactions in these mixtures. The results indicate the presence of specific interactions among the AN and PEG molecules, which follow the order PEG200 < PEG300 < PEG400.     

Evaluation of surface potential from single crystal electrode potential

The new method of evaluation of the point of zero potential for the metal oxide exhibiting a saddle-like surface potential function Ψ ₀(pH), as obtained by acid base potentiometric titration using Single Crystal Electrode, was proposed. The electrode potential of sapphire single crystal electrode (A crystal plane, $11\bar{2}0$ ) was measured, point of zero potential and surface potentials were evaluated, and the results were analyzed using the Surface Complexation Model. The electroneutrality point corresponding to the point of zero potential was found to be at pH_pzp=7.0. Thermodynamic protonation equilibrium constants for the first and the second step of protonation were obtained as $\lg K_{1}^{\circ} = 12.7$ ; $\lg K_{2}^{\circ} = 1.2$ .     

Thermodynamic Analysis of Homologous α-Amino Acids in Aqueous Potassium Fluoride Solutions at Different Temperatures

Partial molal volumes ( $V_{\phi} ^{0}$ ) and partial molal compressibilities ( $K_{\phi} ^{0}$ ) for glycine, L-alanine, L-valine and L-leucine in aqueous potassium fluoride solutions (0.1 to 0.5?mol?kg^?1) have been measured at T=(303.15,308.15,313.15 and 318.15) K from precise density and ultrasonic speed measurements. Using these data, Hepler coefficients ( $\partial^{2}V_{\phi} ^{0}/\partial T^{2}$ ), transfer volumes ( $\Delta V_{\phi} ^{0}$ ), transfer compressibilities ( $\Delta K_{\phi} ^{0}$ ) and hydration number (n _H) have been calculated. Pair and triplet interaction coefficients have been obtained from the transfer parameters. The values of $V_{\phi} ^{0}$ and $K_{\phi} ^{0}$ vary linearly with increasing number of carbon atoms in the alkyl chain of the amino acids. The contributions of charged end groups ( $\mathrm{NH}_{3}^{+}$ , COO^?), CH₂ group and other alkyl chains of the amino acids have also been estimated. The results are discussed in terms of the solute?Ccosolute interactions and the dehydration effect of potassium fluoride on the amino acids.     

Specific heat capacity and thermodynamic properties of CuTeO3 and HgTeO3

Tellurites of CuTeO₃ and HgTeO₃ are synthesized and their specific molar heat capacities are experimentally determined for the first time. The tellurites discussed in the present paper are used for preparation of optical glasses with special properties for optoelectronics, nuclear and power industries. The tellurites synthesized are prepared for chemical analysis, differential thermal analysis and X-ray analysis. The use of the tellurites studied is related to knowing their thermodynamic properties like specific molar heat capacity (C _p,m), enthalpy \( \left( {\Delta_{{{\text {T}}^{\prime}}}^{\text{T}} H_{\text{m}}^{0} } \right), \) entropy \( \left( {\Delta_{{{\text {T}}^{\prime}}}^{\text{T}} S_{\text{m}}^{0} } \right) \) and Gibbs energy \( \left( { - \Delta_{{{\text {T}}^{\prime}}}^{\text{T}} G_{\text{m}}^{0} } \right) \) . The temperature dependences of their molar heat capacities are determined using the least squares method. The thermodynamic properties are calculated: entropy, enthalpy and Gibbs function.     

Crystal structure and thermodynamic properties of dipotassium diiron(III) hexatitanium oxide

In the present work, the temperature dependence of heat capacity of dipotassium diiron(III) hexatitanium oxide has been measured for the first time in the range from 10 to 300 K by means of precision adiabatic vacuum calorimetry. The experimental data were used to calculate standard thermodynamic functions, namely the heat capacity $ C_{p}^{ \circ } (T) $ , enthalpy $ H^{ \circ } (T) - H^{ \circ } (0) $ , entropy $ S^{ \circ } (T) - S^{ \circ } (0), $ and Gibbs function $ G^{ \circ } (T) - H^{ \circ } (0) $ for the range from T → 0 to 300 K. The structure of K₂Fe₂Ti₆O₁₆ is refined by the Rietveld method: space group I4/m, Z = 1, a = 10.1344(2) Å, c = 2.97567(4) Å, V = 305.618(7) Å³. The high-temperature X-ray diffraction was used for the determination of coefficients of thermal expansion.     

The standard molar enthalpies of formation of chromone-3-carboxylic acid, 6-methylchromone-2-carboxylic acid,and 6-methyl-4-chromanone determined by micro-combustion calorimetry

The energies of combustion of chromone-3-carboxylic acid (C3CA), 6-methylchromone-2-carboxylic acid (6MCC), and 6-methyl-4-chromanone (6M4C) were determined using an isoperibolic micro-combustion calorimeter. The calorimeter used in the present work has been assembled, calibrated, and tested in our laboratory with the desired results. Prior to the measurement of the energies of combustion, the purities, heat capacities (C _p), fusion temperatures (T _fus), and enthalpies of melting (Δ_fus H) for each compound were determined by differential scanning calorimetry. The values of the energies of combustion were used to derive standard molar enthalpies of combustion ( \( \Delta _{{\text{c}}} H_{{\text{m}}}^{\circ } \) ) and standard molar enthalpies of formation ( \( \Delta _{{\text{f}}} H_{{\text{m}}}^{\circ } \) ) in the crystalline phase at T = 298.15 K. The values found for the \( \Delta _{{\text{f}}} H_{{\text{m}}}^{\circ } \) of C3CA, 6MCC, and 6M4C were ?(619.5 ± 2.6), ?(656.2 ± 2.2), and ?(308.9 ± 3.0) kJ mol^?1, respectively.     

Apparent molal volumes of butylammonium chlorides and sodium butanecarboxylates in dilute aqueous solutions

The densities of dilute aqueous solutions of the isomers of butylammonium chlorides (n-, iso-, sec-, andtert-BuNH₃Cl) and sodium butanecarboxylates (n-, iso-, sec-, andtert-BuCOONa) have been determined at 5, 25, and 45°C using a buoyancy technique. The limiting partial molal volumes \(\bar V^\circ\) and expansibilities of the solutes have been evaluated. The branching of alkyl chain causes larger \(\bar V^\circ\) values for BuNH₃Cl series but smaller values for BuCOONa series. The \(\bar V^\circ\) values of branched isomers have been calculated using the data for volume increment accompanying methyl substitution. Good agreement with the experimental values was obtained. It is suggested that the volumetric behavior of the organic electrolytes studied is governed by the influences of the ionic groups on the hydrophobic hydration. The results have been compared with the data for butanol isomers.     

Densities and Volumetric Properties of Butyl Acrylate + 1-Butanol, or +2-Butanol, or +2-Methyl-1-propanol, or +2-Methyl-2-propanol Binary Mixtures at Temperatures from 288.15 to 318.15 K

The densities, ρ, of binary mixtures of butyl acrylate with 1-butanol, 2-butanol, 2-methyl-1-propanol, and 2-methyl-2-propanol, including those of the pure liquids, were measured over the entire composition range at temperatures of (288.15, 293.15, 298.15, 303.15, 308.15, 313.15, and 318.15) K and atmospheric pressure. From the experimental data, the excess molar volume $ V_{\text{m}}^{\text{E}} $ V m E , partial molar volumes $ \overline{V}_{\text{m,1}} $ V ¯ m,1 and $ \overline{V}_{\text{m,2}} $ V ¯ m,2 , and excess partial molar volumes $ \overline{V}_{\text{m,1}}^{\text{E}} $ V ¯ m,1 E and $ \overline{V}_{\text{m,2}}^{\text{E}} $ V ¯ m,2 E , were calculated over the whole composition range as were the partial molar volumes $ \overline{V}_{\text{m,1}}^{^\circ } $ V ¯ m,1 ° and $ \overline{V}_{\text{m,2}}^{^\circ } $ V ¯ m,2 ° , and excess partial molar volumes $ \overline{V}_{\text{m,1}}^{{^\circ {\text{E}}}} $ V ¯ m,1 ° E and $ \overline{V}_{\text{m,2}}^{{^\circ {\text{E}}}} $ V ¯ m,2 ° E , at infinite dilution,. The $ V_{\text{m}}^{\text{E}} $ V m E values were found to be positive over the whole composition range for all the mixtures and at each temperature studied, indicating the presence of weak (non-specific) interactions between butyl acrylate and alkanol molecules. The deviations in $ V_{\text{m}}^{\text{E}} $ V m E values follow the order: 1-butanol < 2-butanol < 2-methyl-1-propanol < 2-methyl-2-propanol. It is observed that the $ V_{\text{m}}^{\text{E}} $ V m E values depend upon the position of alkyl groups in alkanol molecules and the interactions between butyl acrylate and isomeric butanols decrease with increase in the number of alkyl groups at α-carbon atom in the alkanol molecules.     

Thermochemical Properties of n-Undecylammonium Bromide Monohydrate C11H28BrNO(s)

The crystal structure of n-undecylammonium bromide monohydrate was determined by X-ray crystallography. The crystal system of the compound is monoclinic, and the space group is P2₁/c. Molar enthalpies of dissolution of the compound at different concentrations m/(mol·kg^?1) were measured with an isoperibol solution–reaction calorimeter at T = 298.15 K. According to the Pitzer’s electrolyte solution model, the molar enthalpy of dissolution of the compound at infinite dilution ( $ \Updelta_{\text{sol}} H_{\text{m}}^{\infty } $ ) and Pitzer parameters ( $ \beta_{\text{MX}}^{(0)L} $ and $ \beta_{\text{MX}}^{(1)L} $ ) were obtained. Values of the apparent relative molar enthalpies ( $ {}^{\Upphi }L $ ) of the title compound and relative partial molar enthalpies ( $ \bar{L}_{2} $ and $ \bar{L}_{1} $ ) of the solute and the solvent at different concentrations were derived from experimental values of the enthalpies of dissolution.     

On k-resonance of grid graphs on the plane,torus and cylinder

Grid graphs on the plane, torus and cylinder are finite 2-connected bipartite graphs embedded on the plane, torus and cylinder, respectively, whose every interior face is bounded by a quadrangle. Let \(k\) be a positive integer, a grid graph is \(k\) -resonant if the deletion of any \(i \le k\) vertex-disjoint quadrangles from \(G\) results in a graph either having a perfect matching or being empty. If \(G\) is \(k\) -resonant for any integer \(k \ge 1\) , then it is called maximally resonant. In this study, we provide a complete characterization for the \(k\) -resonance of grid graphs \(P_m\times P_n\) on plane, \(C_m\times C_n\) on torus and \(P_m\times C_n\) on cylinder.     

Symmetry-itemized enumeration of RS-stereoisomers of allenes. I. The fixed-point matrix method of the USCI approach combined with the stereoisogram approach

After the RS-stereoisomeric group \(\mathbf{D}_{2d\widetilde{\sigma }\widehat{I}}\) of order 16 has been defined by starting point group \(\mathbf{D}_{2d}\) of order 8, the isomorphism between \(\mathbf{D}_{2d\widetilde{\sigma }\widehat{I}}\) and the point group \(\mathbf{D}_{4h}\) of order 16 is thoroughly discussed. The non-redundant set of subgroups (SSG) of \(\mathbf{D}_{2d\widetilde{\sigma }\widehat{I}}\) is obtained by referring to the non-redundant set of subgroups of \(\mathbf{D}_{4h}\) . The coset representation for characterizing the orbit of the four positions of an allene skeleton is clarified to be \(\mathbf{D}_{2d\widetilde{\sigma }\widehat{I}}(/\mathbf{C}_{s\widetilde{\sigma }\widehat{I}})\) , which is closely related to the \(\mathbf{D}_{4h}(/\mathbf{C}_{2v}^{\prime \prime \prime })\) . According to the unit-subduced-cycle-index (USCI) approach (Fujita, Symmetry and combinatorial enumeration of chemistry. Springer, Berlin 1991), the subduction of \(\mathbf{D}_{2d\widetilde{\sigma }\widehat{I}}(/\mathbf{C}_{s\widetilde{\sigma }\widehat{I}})\) is examined so as to generate unit subduced cycle indices with chirality fittingness (USCI-CFs). Then, the fixed-point matrix method of the USCI approach is applied to the USCI-CFs. Thereby, the numbers of quadruplets are calculated in an itemized fashion with respect to the subgroups of \(\mathbf{D}_{2d\widetilde{\sigma }\widehat{I}}\) . After the subgroups of \(\mathbf{D}_{2d\widetilde{\sigma }\widehat{I}}\) are categorized into types I–V, type-itemized enumeration of quadruplets is conducted to illustrate the versatility of the stereoisogram approach.     

Thermodynamic Solvation of a Series of Homologous α-Amino Acids in Aqueous Mixtures of 1,2-Dimethoxyethane

The standard Gibbs energies $ \left( {\Updelta {}_{\text{t}}G^\circ (i)} \right) $ ( Δ t G ° ( i ) ) and entropies $ \left( {\Updelta {}_{\text{t}}S^\circ } \right) $ ( Δ t S ° ) of transfer in aqueous mixtures of 1,2-dimethoxyethane (DME) containing 0, 20, 40, 60, 80, 100 wt-% DME have been determined from the solubility data of a series of homologous α-amino acids, evaluated by the formol titrimetric method. The observed result of Δ_t G°(i) and TΔ_t S°(i) against DME concentration profiles are complicated due to the various interaction effects. The chemical effects on the transfer Gibbs energies ( $ \Updelta_{\text{t}} G_{\text {ch}}^{ \circ } (i) $ Δ t G ch ° ( i ) ) and entropies of transfer $ T\Updelta_{\text{t}} S_{\text {ch}}^{ \circ } (i) $ T Δ t S ch ° ( i ) have been obtained after elimination of the cavity effect, calculated by the scaled particle theory, and dipole–dipole interaction effects, estimated by the use of Keesom-orientation expression for total transfer Gibbs energies Δ_t G°(i) and entropies Δ_t S°, respectively. The chemical transfer energetics of the zwitterionic homologous α-amino acids are guided by the composite effects of increased dispersion interaction, basicity and decreased acidity, hydrogen bonding capacity and hydrophobic hydration of the DME mixed solvent as compared to that of reference solvent, water.     

Thermodynamic behavior of complexation process between benzo-15-crown-5 with Li+, Na+, K+, and NH4 + cations in acetonitrile–methanol binary media

The stability constants of 1:1 (M:L) complexes of benzo-15-crown-5 (B15C5) with Li⁺, Na⁺, K⁺ and NH₄ ⁺ cations, the Gibbs standard free energies ( $ \Updelta {\text{G}}_{\text{c}}^{ \circ } $ ), the standard enthalpy changes ( $ \Updelta {\text{H}}_{\text{c}}^{ \circ } $ ) and standard entropy changes ( $ \Updelta {\text{S}}_{\text{c}}^{ \circ } $ ) for formation of these complexes in acetonitrile–methanol (AN–MeOH) binary mixtures have been determined conductometrically. The conductance data show that the stoichiometry of the complexes formed between the macrocyclic ligand and the studied cations is 1:1 (M:L). In most cases, addition of B15C5 to solutions of these cations, causes a continuous increase in the molar conductivities which indicates that the mobility of complexed cations is more than the uncomplexed ones. The stability constants of the complexes were obtained from fitting of molar conductivity curves using a computer program, GENPLOT. The results show that the selectivity order of B15C5 for the metal cations changes with the nature and composition of the binary mixed solvent. The values of standard enthalpy changes ( $ \Updelta {\text{H}}_{\text{c}}^{ \circ } $ ) for complexation reactions were obtained from the slope of the van’t Hoff plots and the changes in standard entropy ( $ \Updelta {\text{S}}_{\text{c}}^{ \circ } $ ) were calculated from the relationship $ \Updelta {\text{G}}_{{{\text{c}},298.15}}^{ \circ } = \Updelta {\text{H}}_{\text{c}}^{ \circ } - 298.15\Updelta {\text{S}}_{\text{c}}^{ \circ } $ . A non-linear behavior was observed between the stability constants (log K_f) of the complexes and the composition of the acetonitrile–methanol (AN–MeOH) binary solution. The results obtained in this study, show that in most cases, the complexes formed between B15C5 and Li⁺, Na⁺, K⁺ and NH₄ ⁺ cations are both enthalpy and entropy stabilized and the values of these thermodynamic quantities change with the composition of the binary solution.