Enthalpy of solution of tigogenin saponin in dioxane and the temperature dependence of its heat capacity

The heats of solution of tigogenin C₂₇H₄₄O₃ in dioxane at dilutions equal to 1: 9000, 1: 18 000, and 1: 36 000 (mol solute/mol solvent) have been studied by isothermal calorimetry. The standard enthalpy of C₂₇H₄₄O₃ solution in dioxane at infinite dilution was derived by the mathematical processing of the calorimetric data. Dynamic calorimetry over the range 173–423 K has been used to study the heat capacity of tigogenin. The C _p ^o ～ f(T) plot has a jump at 298.15. K. The standard enthalpies of formation and combustion and the heat of melting of tigogenin have been indirectly calculated.     

Thermodynamic Properties of Dimethylaminoarglabin Methyl Iodide C1 8H2 8O3NI and Its Analogs

The heat of solution of dimethylaminoarglabin methyl iodide C_{1 8}H_{2 8}O₃NI at dilutions (mole of salt/mole of water) of 1 : 75000, 1 : 100000, and 1 : 150000 was determined by isothermal calorimetry. The data obtained were used to calculate the standard heat of solution of the compound in an infinitely dilute (standard) aqueous solution. The heats of combustion, melting, and formation of C_{1 8}H_{2 8}O₃NI and 33 its analogs were estimated by approximate methods of chemical thermodynamics.     

Thermodynamic properties of biologically active substances: 3-acetyl-9-methoxy-2-phenyl-11H-indolizino[8,7-b]indole and 8-acetylharmine

The enthalpies of solution of 3-acetyl-9-methoxy-2-phenyl-11H-indolizino[8,7-b]indole and 8-acetylharmine in dimethyl sulfoxide were measured by isothermal calorimetry at solute: solvent molar ratios of 1: 9000, 1: 18000, and 1: 36000. From the data obtained, the standard enthalpies of solution of the compounds in dimethyl sulfoxide at infinite dilution were calculated. The heat capacities of 8-acetylharmine were determined by dynamic calorimetry in the interval 298.15–673 K, and the C _p ^o = f(T) equations were obtained. The standard enthalpies of combustion of the compounds were estimated by approximate methods, and their heats of melting were calculated. From the data obtained, using Hess cycle, the standard enthalpies of formation of the compounds were calculated.     

过渡金属离子液体的热化学性质研究BMIC/ZnCl2体系

在干燥的氩气氛中, 于363 K下缓慢混合等摩尔的氯化1-甲基-3-丁基咪唑(BMIC)和高纯无水ZnCl2, 得到了无色透明的离子液体BMIC/ZnCl2. 在298.15 K下, 用具有恒温环境的溶解反应热量计测定了不同浓度离子液体BMIC/ZnCl2在水中的溶解焓, 依据Pitzer方程拟合得到它们的标准摩尔溶解焓ΔsH0m和Pitzer溶解焓参数. 利用标准摩尔溶解焓估算了离子液体的水化焓.     

Thermodynamic characteristics of the complex formation in the zinc(II) ion-L-serine-water system

Using calorimetric method we determined the thermal effects of reactions of the L-serine complex formation with the doubly charged zinc ion. The heat effects of the reaction of amino acid solution with a solution of zinc(II) were measured at temperatures 288.15, 298.15, and 308.15 K and ionic strengths 0.25, 0.50, and 0.75, against the background of KNO₃. The heats of dilution of zinc nitrate in the background electrolyte solution were determined under the same conditions, to introduce respective corrections. The thermochemical data were processed with accounting for all the possible equilibria. The standard thermodynamic characteristics of complex formation processes were calculated. The effects of concentration and temperature on the thermal effects of the complex formation of zinc(II) and L-serine in aqueous solution were estimated.     

Isopiestic Determination of the Osmotic and Activity Coefficients of Li2SO4(aq) at T=298.15 and 323.15 K, and Representation with an Extended Ion-Interaction (Pitzer) Model

Isopiestic vapor-pressure measurements were made for Li₂SO₄(aq) from 0.1069 to 2.8190 mol?kg^?1 at 298.15 K, and from 0.1148 to 2.7969 mol?kg^?1 at 323.15 K, with NaCl(aq) as the reference standard. Published thermodynamic data for this system were reviewed, recalculated for consistency, and critically assessed. The present results and the more reliable published results were used to evaluate the parameters of an extended version of Pitzer’s ion-interaction model with an ionic-strength dependent third-virial coefficient, as well as those of the standard Pitzer model, for the osmotic and activity coefficients at both temperatures. Published enthalpies of dilution at 298.15 K were also analyzed to yield the parameters of the ion-interaction models for the relative apparent molar enthalpies of dilution. The resulting models at 298.15 K are valid to the saturated solution molality of the thermodynamically stable phase Li₂SO₄?H₂O(cr). Solubilities of Li₂SO₄?H₂O(cr) at 298.15 K were assessed and the selected value of m(sat.)=3.13±0.04 mol?kg^?1 was used to evaluate the thermodynamic solubility product K _s(Li₂SO₄?H₂O, cr, 298.15 K) = (2.62±0.19) and a CODATA-compatible standard molar Gibbs energy of formation Δ_f G _m ^o (Li₂SO₄?H₂O, cr, 298.15 K) = ?(1564.6±0.5) kJ?mol^?1.     

The thermodynamic characteristics of formation of cobalt(II) ion complexes with D,L-threonine in aqueous solution

The heat effects of interaction of cobalt(II) ions with D,L-threonine in aqueous solution and the corresponding heats of dilution were determined by direct calorimetry at 288.15, 298.15, and 308.15 K and ionic strength values of 0.25, 0.50, and 0.75 (against the background of potassium nitrate). The standard heat effects of formation of CoThr⁺, CoThr₂, and CoThr ₃ ^? complexes were determined by extrapolation to zero ionic strength according to the equation with one individual parameter. The standard enthalpies of formation of complex particles in the hypothetical nondissociated state in aqueous solution were calculated.     

Thermochemical study of coordination equilibria in the zinc(II)-β-alanine-water system in aqueous solution

The heats of formation of β-alanine (HAla) complexes with Zn²⁺ ion at temperatures of 288.15, 298.15, and 308.15 K and ionic strengths of 0.25, 0.50, and 0.75 mol/l (KNO₃) were determined by calorimetry; the heats of dilution of a zinc nitrate solution in supporting electrolyte solutions were found for introduction of appropriate corrections. The standard heats of complexation in the zinc(II)-β-alanine-water system were determined. The standard thermodynamic characteristics of zinc(II) complexation with β-alanine and standard enthalpies of formation of ZnAla⁺ and ZnAla₂ complex species were calculated.     

Sorption,diffusion, and permeation of ethylbenzene in poly(1‐trimethylsilyl‐1‐propyne)

The solubility, diffusivity, and permeability of ethylbenzene in poly(1‐trimethylsilyl‐1‐propyne) (PTMSP) at 35, 45 and 55 °C were determined using kinetic gravimetric sorption and pure gas permeation methods. Ethylbenzene solubility in PTMSP was well described by the generalized dual‐mode model with χ = 0.39 ± 0.02, b = 15 ± 1, and C^′_H = 45 ± 4 cm³ (STP)/cm³ PTMSP at 35 °C. Ethylbenzene solubility increased with decreasing temperature; the enthalpy of sorption at infinite dilution was −40 ± 7 kJ/mol and was essentially equal to the enthalpy change upon condensation of pure ethylbenzene. The diffusion coefficient of ethylbenzene in PTMSP decreased with increasing concentration and decreasing temperature. Activation energies of diffusion were very low at infinite dilution and increased with increasing concentration to a maximum value of 50 ± 10 kJ/mol at the highest concentration explored. PTMSP permeability to ethylbenzene decreased with increasing concentration. The permeability estimated from solubility and diffusivity data obtained by kinetic gravimetric sorption was in good agreement with permeability determined from direct permeation experiments. Permeability after exposure to a high ethylbenzene partial pressure was significantly higher than that observed before the sample was exposed to a higher partial pressure of ethylbenzene. Nitrogen permeability coefficients were also determined from pure gas experiments. Nitrogen and ethylbenzene permeability coefficients increased with decreasing temperature, and infinite dilution activation energies of permeation for N₂ and ethylbenzene were −5.5 ± 0.5 kJ/mol and −74 ± 11 kJ/mol, respectively. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1078–1089, 2000     

Thermodynamic studies on water-β-cyclodextrin-surfactant ternary systems

Conductance measurements are reported for double chain surfactants like N,N,N-octylpentyldimethylammonium (OPAC) and N,N,N-octyloctyldimethylammonium chlorides (OOAC) in water-β-cyclodextrin solution. From the specific conductivity data, the apparent critical micelle concentration (cmc¹) and the degree of counterion dissociation (β) were obtained at a fixed β-CD concentration (m_βCD = 0.01190 mol kg⁻¹, besides from the cmc¹ value and that in water (cmc) the stoichiometry of the surfactant-β-CD complex was calculated. Densities, heat capacities, enthalpies of dilution at 298 K and osmotic coefficients at 310 K were measured for the same systems; the apparent molar volumes, V_λ, and heat capacities, C_λ, of two surfactants in β-CD solution, calculated as functions of surfactant concentrations m_s, have made possible to obtain the properties of transfer of the surfactant from water to β-CD-water solutions.     

The thermodynamic parameters of complex formation between the copper(II) Ion and β-alanine in aqueous solution

The heats of formation of β-alanine complexes with the doubly charged copper(II) ion were determined calorimetrically. The heat effects of interaction of a solution of the amino acid with a solution of copper(II) were measured at 288.15, 298.15, and 308.15 K and ionic strengths of 0.50, 0.75, and 1.00 against the background of KNO₃. The heats of dilution of a solution of copper nitrate with solutions of the background electrolyte were also determined for the introduction of the corresponding corrections. The standard thermodynamic characteristics of complex formation were calculated. The influence of temperature on the thermal effects of complex formation in the β-alanine-copper(II) ions system were considered. The standard enthalpies of formation of CuAla⁺ and CuAla₂ complex particles in aqueous solution were calculated.     

Thermochemistry of sesquiterpene lactone argolide

The enthalpies of dissolution of argolide (C₁₅H₂₀O₃) in 96% ethanol are determined by isothermal calorimetry at 298.15 K and different dilutions of 1: 18 000, 1: 36 000, and 1: 72 000 (by mole). The standard enthalpy of dissolution of argolide in 96% ethanol is calculated from the obtained data: (86 ± 17) kJ mol^?1. The temperature dependence of heat capacity of C₁₅H₂₀O₃ is studied by means of dynamic calorimetry. An equation is derived to describe the С _p ⁰ ~ f (Т) dependence, and the standard heat capacity at 298.15 K is found to be (393 ± 13) J mol^?1 K^?1. The enthalpies of combustion, fusion and formation of argolide are calculated via approximation.     

Thermodynamic characteristics of the formation of Cd2+ ion-L-serine complexes in aqueous KNO3 solutions at 288–308 K

The heats of formation of complexes of L-serine and doubly charged cadmium ions are determined by calorimetry. The heat effects of the reaction between an amino acid solution and a cadmium(II) solution and the respective heats of dilution of cadmium nitrate solution are measured at temperatures of 288.15, 298.15, and 308.15 K and ionic strengths of 0.25, 0.50, and 0.75 against the background of KNO₃. The standard thermodynamic characteristics of complexation are calculated. Standard enthalpies of formation of mono-, bis-, and tris-coordinated complexes of cadmium(II) in an aqueous solution are found.     

Molar Volumes and Heat Capacities of Electrolytes and Ions in Nonaqueous Solvents: 1. Formamide

Apparent molar volumes and heat capacities of 27 electrolytes have been measured as a function of concentration in formamide at 25°C using a series-connected flow densimeter and Picker calorimeter system. These data were extrapolated to infinite dilution using the appropriate Debye–Hückel limiting slopes to give the corresponding standard partial molar quantities. Ionic volumes and heat capacities at infinite dilution were obtained by an appropriate assumption based on the reference electrolyte Ph₄PBPh₄ (TPTB). The ionic volumes, but not the heat capacities, agree reasonably well with previously published statistically based predictions. The values obtained are discussed in terms of simple models of electrolyte solution behavior and a number of interesting features are noted, including, possible dependencies of ionic volumes on solvent isothermal compressibility and of ionic heat capacities on solvent electron acceptor abilities.     

Thermal degradation study of isotactic polypropylene using factor-jump thermogravimetry

The degradation of isotactic polypropylene in the range 390–465°C was studied using factor-jump thermogravimetry. The degradations were carried out in vacuum and at pressures of 5 and 800 mm Hg of N₂, flowing at 100–400 standard mL/s. At 800 mm Hg this corresponds to linear rates of 1–4 mm/s. In vacuum bubbling in the sample caused problems in measuring the rate of weight loss. The apparent activation energy was estimated as 61.5 ± 0.8 kcal/mol (257 ± 3 kJ/mol). In slowly flowing N₂ at 800 mm Hg pressure the activation energy was 55.1 ± 0.2 kcal/mol (230 ± 0.8 kJ/mol) for isotactic polypropylene and 51.1 ± 0.5 kcal/mol (214 ± 2 kJ/mol) for a naturally aged sample of atactic polypropylene. For isotactic polypropylene degrading at an external N₂ pressure of 5 mm Hg the apparent activation energy was 55.9 ± 0.3 kcal/mol (234 ± 1 kJ/mol). A simplified degradation mechanism was used with estimates of the activation energies of initiation and termination to give an estimate of 29.6 kcal/mol for the ß-scission of tertiary radicals on the polypropylene backbone. Initiation was considered to be backbone scission ß to allyl groups formed in the termination reaction. For initiation by random scission of the polymer backbone, as in the early stages of thermal degradation, an overall activation energy of 72 kcal/mol is proposed. The difference between vacuum and in-N₂ activation energies is ascribed to the latent heat contributions of molecules which do not evaporate as soon as they are formed. At these imposed rates of weight loss the average molecular weights of the volatiles in vacuum and in 8 and 800 mm H_g N₂ are in the ratios 1–1/2–1/9.     

Heats of dilution of trialkyl phosphates in iso-octane and carbon tetrachloride: Interpretation in terms of self-association

The heats of solution and dilution of triethyl phosphate (TEP), tripropyl phosphate (TPP), and tributyl phosphate (TBP) in iso-octane have been measured at 25°C. The enthalpy of dilution was found to decrease with hydrocarbon chain length. The resulting apparent molal heat content, φ_L, values are interpreted in terms of the degree and nature of the associated species present assuming that the heat of dilution is essentially due to the breakdown of the various associated species. The results are consistent with a monomer-to-dimer model. Equilibrium constants and enthalpy change values are calculated for the dimerization reaction. The heat of dilution of TBP in carbon tetrachloride was exothermic rather than endothermic, indicating significant solute-solvent interaction.     

Conformational contribution to the heat capacity of the starch and water system

The heat capacities of starch and starch—water have been measured with adiabatic calorimetry and standard differential scanning calorimetry and are reported from 8 to 490 K. The amorphous starch containing 11–26 wt % (53–76 mol %) water shows a partial glass transition decreasing from 372 to 270 K, respectively. Even the dry amorphous starch gradually increases in heat capacity above 270 K beyond that set by the vibrational density of states. This gradual increase in the heat capacity is identified as part of the glass transition of dry starch that is, however, not completed at the decomposition temperature. The heat capacities of the glassy, dry starch are linked to an approximate group vibrational spectrum with 44 degrees of freedom. The Tarasov equation is used to estimate the heat capacity contribution due to skeletal vibrations with the parameters Θ₁ = 795.5 K, Θ₂ = 159 K, and Θ₃ = 58 K for 19 degrees of freedom. The calculated and experimental heat capacities agree better than ±3% between 8 and 250 K. Similarly, the vibrational heat capacity has been estimated for glassy water by being linked to an approximate group vibrational spectrum and the Tarasov equation (Θ₁ = 1105.5 K and Θ₃ = 72.4 K, with 6 degrees of freedom). Below the glass transition, the heat capacity of the solid starch—water system has been estimated from the appropriate sum of its components and also from a direct fitting to skeletal vibrations. Above the glass transition, the differences are interpreted as contributions of different conformational heat capacities from chains of the carbohydrates interacting with water. The conformational parts are estimated from the experimental heat capacities of dry starch and starch—water, decreased by the vibrational and external contributions to the heat capacity. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 3038–3054, 2001     

Phase Equilibria in Systems DyCuS<Subscript>2</Subscript>–EuS and Cu<Subscript>2</Subscript>S−Dy<Subscript>2</Subscript>S<Subscript>3</Subscript>−EuS

The phase diagram of system DyCuS₂–EuS has been first constructed, and the phase equilibria in the Cu₂S–Dy₂S₃–EuS triangle at 970 K have been studied. Compound EuDyCuS₃ (1DyCuS₂ : 1EuS), space group Pnma, a = 10.1901(3) Å, b = 3.9270(1) Å, c = 12.8468(3) Å, melts incongruently at 1727 ± 7 K according to the reaction: EuDyCuS_3solid ? 0.17 SS EuS (90 mol % EuS, 10 mol % DyCuS₂) + 0.83 liq (42 mol % EuS, 58 mol % DyCuS₂), ΔH = 2.9 ± 0.6 kJ/mol; microhardness of the phase is 3080 ± 35 MPa. Compound EuDyCuS₃ is transparent in the range 3000–1800 cm^–1. In system DyCuS₂–EuS, the solid solution (SS) based on EuS extends from 91 to 100 mol % at 1770 K and from 92 to 100 mol % at 1170 K. In γ-DyCuS₂, 2 mol % EuS dissolves at 1487 K. The eutectic is formed between compounds DyCuS₂ and EuDyCuS3 at 12 mol % EuS, T = 1487 ± 8 K. In system Cu₂S?Dy₂S₃?EuS, 10 secondary systems have been isolated. At 970 K, tie-lines are located between compound EuDyCuS₃ and solid solutions based on compounds β-Cu₂S, EuS, DyCuS₂, β-(DyCu₃S₃), and EuDy₂S₄; between DyCuS₂ and the solid solution of α-Dy₂S₃, DyCuS₂, and EuDy₂S₄.     

Selective Extraction of Sinapic Acid Derivatives from Mustard Seed Meal by Acting on pH: Toward a High Antioxidant Activity Rich Extract

The aim of this paper is to study the effect of the pH on the extraction of sinapic acid and its derivatives from mustard seed meal. Solutions of acidic pH (pH 2), basic pH (pH 12) and distilled water (uncontrolled pH ~ 4.5) were tested at different percentages of ethanol. The maximum extraction yield for sinapic acid (13.22 µmol/g of dry matter (DM)) was obtained with a buffered aqueous solution at pH 12. For ethyl sinapate, the maximum extraction yield reached 9.81 µmol/g _DM with 70% ethanol/buffered aqueous solution at pH 12. The maximum extraction yield of sinapine (15.73 µmol/g _DM) was achieved with 70% ethanol/buffered aqueous solution at pH 2. The antioxidant activity of each extract was assessed by DPPH assay; the results indicated that the extracts obtained at pH 12 and at low ethanol percentages (<50%) exhibit a higher antioxidant activity than extracts obtained at acidic conditions. Maximum antioxidant activity was reached at pH 12 with buffer solution (11.37 mg of Trolox Equivalent/g _DM), which confirms that sinapic acid-rich fractions exhibit a higher antioxidant activity. Thus, to obtain rich antioxidant extracts, it is suggested to promote the presence of sinapic acid in the extracts.     

Thermodynamics of aqueous gallium chloride. Heats of solution and dilution at 25°C

The heat of solution of GaCl₃ and heats of dilution of single GaCl₃ solutions in water and of mixed GaCl₃−HCl solutions in HCl solutions (with a fixed HCl concentration of 0.1337 mol-kg⁻¹ HCl) up to 4 mol-kg⁻¹ GaCl₃ were measured at 25°C. While in the acid solutions hydrolysis is suppressed to below 0.5% of total gallium concentration, the measurements in water allow evaluation of the effect of hydrolysis on the relative enthalpy. The Pitzer interaction model for excess properties of aqueous electrolytes was used to interpret the change in relative enthalpy with concentration. Pitzer parameters were derived by statistical inference using ridge regression. Their physical significance is supported by the heat of solution data. The measurements yield the following results for standard heats of formation and Pitzer parameters for the relative molar enthalpy at 25°C: With these parameters the overall variance in the partial molar heat of solution at infinite dilution, extrapolated from the present experiments, is minimized to 0.35 kJ²-mol⁻², while the experimental apparent molar heats of dilution are reproduced on average within 2.7 kJ-mol⁻¹.