Dominant factors affecting the pressure dependence of melting temperatures in homologous series of aliphatic polyesters

The pressure dependence of the melting temperature of six aliphatic polyesters belonging to two different homologous series, poly(x-succinate) and poly(x-adipate) having even number of methylene groups (2,4,6) in the alkylene segment (x) was investigated by high pressure differential thermal analysis (HP-DTA) up to 500 MPa. The phase diagrams of these polyesters were newly determined except for poly(ethylene adipate). The dT_m/dp_o at atmospheric pressure was obtained from the quadratic equation and the trend of dT_m/dp_o with respect to the number of methylene groups in the monomer unit in each homologous series is discussed. Amorphous densities at 25 °C, expansion and compressibility coefficients in the melt of these polyesters are also reported. The entropy of fusion (ΔS_m), enthalpy of fusion (ΔH_m), volume change on melting (ΔV_m), conformational entropy (ΔS^or) and volume entropy (ΔS^v) were correlated with respect to the number of methylene groups in the alkylene segment. ΔV_m and ΔS^v displayed a similar trend as that of dT_m/dp_o while ΔS_m, ΔS^or and ΔH_m showed an increasing trend. The influence of these parameters on dT_m/dp_o is discussed in the context of the Clapeyron equation.     

Conformational properties ofn-alkanes

Values of the conformational entropy contributionΔS _c to the melting entropyΔS _m are calculated from a recently reported equation of state (Jain and Simha), and compared with theoretical valuesS _c derived from the rotational isomeric state approximation. For the shortern-alkanesΔS _c is considerably larger thanS _c , whereas for the longern-alkanes the conformational entropy contribution can approximately be described with the rotational isomeric state model. Equations are presented for the calculation of specific volumes at the melting temperature as a function of chain length.     

Compensation effect in the thermodynamics of conformational equilibria

The solvent dependence of thermodynamic parameters of conformational equilibria in trans-1,2-dichlorocyclohexane and trans-1,2-bromochlorocyclohexane was investigated by infrared absorption spectra. The results obtained show the existence of a compensation effect in the thermodynamics of conformational equilibria: the enthalpy (ΔH₀) and entropy (ΔS₀) differences change in the same direction when going from one solvent to another. A semi-quantitative estimation of the effect is given on the basis of the equations of statistical thermodynamics. It is shown that the temperature dependence of the ΔS₀ value must be taken into account when determining the enthalpy difference of the conformers. This yields the equality of the true and observed ΔH₀ values.     

Molar heat capacities and standard molar enthalpy of formation of pyrimethanil butanedioic salt

A noval anilino-pyrimidine fungicide, pyrimethanil butanedioic salt (C₂₈H₃₂N₆O₄), was synthesized by a chemical reaction of pyrimethanil and butanedioic acid. The low-temperature heat capacities of the compound were measured with an adiabatic calorimeter from 80 to 380 K. The thermodynamic function data relative to 298.15 K were calculated based on the heat capacity fitted curve. The thermal stability of the compound was investigated by TG and DSC. The TG curve shows that pyrimethanil butanedioic salt starts to sublimate at 455.1 K and totally changes into vapor when the temperature reaches 542.5 K with the maximal speed of weight loss at 536.8 K. The melting point, the molar enthalpy (Δ_fus H _m), and entropy (Δ_fus S _m) of fusion were determined from its DSC curves. The constant-volume energy of combustion (Δ_c U _m) of pyrimethanil butanedioic salt was measured by an isoperibol oxygen-bomb combustion calorimeter at T = (298.15 ± 0.001) K. From the Hess thermochemical cycle, the standard molar enthalpy of formation was derived and determined to be Δ_f H _m ^o (pyrimethanil butanedioic salt)=?285.4 ± 5.5 kJ mol^?1.     

Effects of sizes of nano-copper oxide on the equilibrium constant and thermodynamic properties for the reaction in nanosystem

Thermodynamic properties and equilibrium constant of reaction in nanosystems were analyzed theoretically. The effects of sizes of nano-CuO on thermodynamic properties and equilibrium constant were studied using the reaction of nano-copper oxide and sodium bisulfate as a system. The experimental results indicate that with the sizes of reactant decreasing, the molar Gibbs free energy (Δ_rG_m), the molar enthalpy (Δ_rH_m) and the molar entropy (Δ_rS_m) decrease, but the equilibrium constant (K) increases and there are linear trends between the reciprocal of sizes for nano-CuO and the values of Δ_rG_m, Δ_rH_m, Δ_rS_m and Ln K, which are in agreement with the theoretical analysis.     

Thermal stability of lysozyme and myoglobin in the presence of anionic surfactants

The interactions of lysozyme and myoglobin with anionic surfactants (hydrogenated and fluorinated), at surfactant concentrations below the critical micelle concentration, in aqueous solution were studied using spectroscopic techniques. The temperature conformational transition of globular proteins by anionic surfactants was analysed as a function of denaturant concentration through absorbance measurements at 280 nm. Changes in absorbance of protein-surfactant system with temperature were used to determine the unfolding thermodynamics parameters, melting temperature, T _m, enthalpy, ΔH _m, entropy, ΔS _m and the heat capacity change, ΔC _p, between the native and denatured states.     

Low-temperature heat capacity and thermodynamic properties of crystalline carboxin (C12H13NO2S)

Carboxin was synthesized and its heat capacities were measured with an automated adiabatic calorimeter over the temperature range from 79 to 380 K. The melting point, molar enthalpy (Δ_fusH_m) and entropy (Δ_fusS_m) of fusion of this compound were determined to be 365.29±0.06 K, 28.193±0.09 kJ mol⁻¹ and 77.180±0.02 J mol⁻¹ K⁻¹, respectively. The purity of the compound was determined to be 99.55 mol% by using the fractional melting technique. The thermodynamic functions relative to the reference temperature (298.15 K) were calculated based on the heat capacity measurements in the temperature range between 80 and 360 K. The thermal stability of the compound was further investigated by differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis. The DSC curve indicates that the sample starts to decompose at ca. 290 °C with the peak temperature at 292.7 °C. The TG-DTG results demonstrate the maximum mass loss rate occurs at 293 °C corresponding to the maximum decomposition rate.     

Adsorption thermodynamic and desorption studies of U(VI) on modified silica gel (SiAPMS-HL)

In this study, the adsorption process was examined by various isotherm models Langmuir, Freundlich and Dubinin–Radushkevich and equilibrium data were successfully described by Langmuir model. Adsorption thermodynamics of uranium (VI) on modified silica gel (SiAPMS-HL) has been studied within a temperature range from 293 to 333 K and the thermodynamic parameters, such as equilibrium constant (K _D), standard free energy changes (ΔG°), standard enthalpy change (ΔH°) and standard entropy change (ΔS°), have been obtained. The desorption studies were conducted in batch system to investigate the kind, concentration and volume of the eluent.     

Thermodynamic properties affect the molecular motion of novolac type phenolic resin blended with polyamide

The effect of association reaction length on the substantial increase of molecular motion as well as entropy (−TΔS_m) of phenolic-polyamide blends is investigated with the ¹³C solid-state NMR and DSC. The H-bonding strength by forming the phenolic-polyamide interaction is great enough to overcome the breaking off the self-association of phenolic. With respect to decreasing the association reaction, the polyamide resonance intensity of ¹³C solid-state NMR spectra is weakened due to the reduction of the cross-polarization efficiency at a high mobile sample. The glass transition temperature of phenolic-polyamide blend as well as T^H_1ρ value from NMR experiments is also decreased. The decreasing strength of H-bonding resulting from blending causes higher entropy (−TΔS_m) and higher molecular mobility of the phenolic-polyamide blends. Accordingly, the polyamide-66 possesses higher H-bonding force and exhibits more mobile role in this phenolic/polyamide blends family. It can be concluded that the molecular segmental motion and entropy are progressively decreased while increasing the inter-association force of the polyamide within the miscible window.     

Determination of the thermodynamic quantities of uranium(VI)–carboxylate complexes by microcalorimetry

Potentiometric and microcalorimetric titration techniques were applied for the determination of the Gibbs free energies and enthalpies of the protonation and U(VI) complexation of some carboxylic acids (formic, acetic, glycolic, and propionic acids) in 1.0 M NaClO₄ solution at 25 °C. By using the values of ΔG determined by potentiometric titrations, the results of calorimetric titrations were analyzed to give the values of ΔH and ΔS. These enthalpy values indicated that the protonation and uranyl(VI) complexation of these carboxylates were mainly entropy-driven, that is, ∣–TΔS∣ ≫ ∣ΔH∣ in ΔG = ΔH − TΔS. The comparison of TΔS_m values for uranyl acetate and glycolate complexation with those for europium(III) complexation revealed that the complexation of U(VI) was accompanied by larger entropy changes due to the limited space in its coordination sphere caused by the steric hindrance of two oxygens in the linear dioxo structure of uranyl ion.     

Isothermal decomposition of ternary oxide AxByOz on an isobar—Stability of perovskite ABO3 (A = La,Sm, Dy; B = Mn,Fe) in a reducing atmosphere

The isothermal decomposition of any ternary oxide A_xB_yO_z on liberation of n moles of oxygen at a constant pressure is found to be driven by the mixing entropy ΔS_m = ?nRln P_O2 of the total entropy change ΔS = ΔS° + ΔS_m. The stability of A_xB_yO_z towards isothermal decomposition into a biphasic solid mixture is derived from the equilibrium condition $\text{ΔG1 = 0}$ as functions of standard changes ΔH° and ΔS°. Assuming ΔS° = 44n and calculating ΔH° in terms of lattice energies U(ABO₃) and U(A₂O₃), the stability of perovskites is given as a function of the ionic radius of the A³⁺ ion. The calculated stability agrees well with that observed. The effect of electronic entropy change ΔS_e on ΔS° is demonstrated for AFeO₃ (A = La, Sm, Dy).     

The adsorption of phosphamidon on the surface of antimony(V) phosphate: A thermodynamic study

The thermodynamics of the adsorption of phosphamidon on antimony(V) phosphate cation exchanger has been studied at 30, 45 and 50°C and the thermodynamic equilibrium constant (K₀), standard free energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°) have been calculated to predict its adsorption behaviour. All the data are adequately represented by the Freundlich isotherms.     

Hydrophobic interaction chromatography of proteins: Thermodynamic analysis of conformational changes

For BSA and β-lactoglobulin adsorption to hydrophobic interaction chromatography (HIC) stationary phases leads to conformational changes. In order to study the enthalpy (ΔH_ads), entropy (ΔS_ads), free energy (ΔG_ads) and heat capacity (Δc_p,ads) changes associated with adsorption we evaluated chromatographic data by the non-linear van’t Hoff model. Additionally, we performed isothermal titration calorimetry (ITC) experiments. van’t Hoff analysis revealed that a temperature raise from 278 to 308 K increasingly favoured adsorption seen by a decrease of ΔG_ads from −12.9 to −20.5 kJ/mol for BSA and from −6.6 to −13.2 kJ/mol for β-lactoglobulin. Δc_p,ads values were positive at 1.2 m (NH₄)₂SO₄ and negative at 0.7 m (NH₄)₂SO₄. Positive Δc_p,ads values imply hydration of apolar groups and protein unfolding. These results further corroborate conformational changes upon adsorption and their dependence on mobile phase (NH₄)₂SO₄ concentration. ITC measurements showed that ΔH_ads is dependent on surface coverage already at very low loadings. Discrepancies between ΔH_ads determined by van’t Hoff analysis and ITC were observed. We explain this with protein conformational changes upon adsorption which are not accounted for by van’t Hoff analysis.     

Heat capacities and thermodynamic properties of 2-benzoylpyridine (C12H9NO)

The heat capacities of 2-benzoylpyridine were measured with an automated adiabatic calorimeter over the temperature range from 80 to 340 K. The melting point, molar enthalpy, Δ_fusH^m, and entropy, Δ_fusS^m, of fusion of this compound were determined to be 316.49±0.04 K, 20.91±0.03 kJ mol^–1 and 66.07±0.05 J mol^–1 K^–1, respectively. The purity of the compound was calculated to be 99.60 mol% by using the fractional melting technique. The thermodynamic functions (H_T–H_298.15) and (S_T–S_298.15) were calculated based on the heat capacity measurements in the temperature range of 80–340 K with an interval of 5 K. The thermal properties of the compound were further investigated by differential scanning calorimetry (DSC). From the DSC curve, the temperature corresponding to the maximum evaporation rate, the molar enthalpy and entropy of evaporation were determined to be 556.3±0.1 K, 51.3±0.2 kJ mol^–1 and 92.2±0.4 J K^–1 mol^–1, respectively, under the experimental conditions.     

Molar heat capacity and thermodynamic properties of 1-cyclohexene-1,2-dicarboxylic anhydride [C8H8O3]

The molar heat capacity C_p,m of 1-cyclohexene-1,2-dicarboxylic anhydride was measured in the temperature range from T=(80 to 360) K with a small sample automated adiabatic calorimeter. The melting point T_m, the molar enthalpy Δ_fusH_m and the entropy Δ_fusS_m of fusion for the compound were determined to be (343.46 ± 0.24) K, (11.88 ± 0.02) kJ · mol⁻¹ and (34.60 ± 0.06) J · K⁻¹ · mol⁻¹, respectively. The thermodynamic functions [H_(T)−H_(298.15)] and [S_(T)−S_(298.15)] were derived in the temperature range from T=(80 to 360) K with temperature interval of 5 K. The mass fraction purity of the sample used in the adiabatic calorimetric study was determined to be 0.9928 by using the fractional melting technique. The thermal stability of the compound was investigated by differential scanning calorimeter (DSC) and thermogravimetric (TG) technique, and the process of the mass-loss of the sample was due to the evaporation, instead of its thermal decomposition.     

Molar heat capacity and thermodynamic properties of 1,2-cyclohexane dicarboxylic anhydride [C8H10O3]

The molar heat capacity C _p,m of 1,2-cyclohexane dicarboxylic anhydride was measured in the temperature range from T=80 to 390 K with a small sample automated adiabatic calorimeter. The melting point T _m, the molar enthalpy Δ_fus H _m and the entropy Δ_fus S _m of fusion for the compound were determined to be 303.80 K, 14.71 kJ mol⁻¹ and 48.43 J K⁻¹ mol⁻¹, respectively. The thermodynamic functions [H _T-H _273.15] and [S _T-S _273.15] were derived in the temperature range from T=80 to 385 K with temperature interval of 5 K. The thermal stability of the compound was investigated by differential scanning calorimeter (DSC) and thermogravimetry (TG), when the process of the mass-loss was due to the evaporation, instead of its thermal decomposition.     

Isothermal titration calorimetry vs. high performance liquid chromatography fingerprint

Chinese Medicine Injections (CMIs) are powerful preparations, but adverse drug reactions can hardly be avoided. Incorrect drug combination is a major cause. Recently, insoluble particulate matter test, pH measurement, and high performance liquid chromatography (HPLC) fingerprint have been recommended as potential strategies for prediction of drug-incompatible reactions. However, these methods were complex to manipulate, subjective to judge, or were of poor relevance and low sensitivity. In this study, a novel application for the detection of compatibility of combination of CMIs based on isothermal titration calorimetry (ITC) has been proposed. Qingkailing Injection (QKL) was selected as a representative drug to blend with Potassium Chloride Injection (KCl) and Calcium Chloride Injection (CaCl₂). The type of reactions between them was intuitively manifested by the thermodynamic parameters including Gibbs free energy change (ΔG), enthalpy change (ΔH), and entropy change (ΔS). The results indicated that when QKL mixed with CaCl₂, ΔG < 0, and |ΔH| > T|ΔS|, which meant chemical changes happened between them and ADRs might happen in clinic. On the contrary, the reactions between QKL and KCl existed solely as physical processes, indicating that it was relatively safe. Meanwhile, HPLC fingerprint was also applied, but no significant difference was found. It is hard to distinguish whether incompatible reactions have happened during HPLC. The study suggested that with the advantages of convenience, sensitivity, and reliability, ITC could serve as an essential tool in the detection of incompatible reactions of drug combination. The described method could be used for early prediction of adverse drug reactions, which would be helpful to ensure the rationality of drug combination.     

High pressure dilatometry on polybutene-1

High pressure dilatometry is used to study the melting processes and the melt of isotactic polybutene-1. Evaluating a great number of isobaricV(T)-curves determined in the range of a few hundred bar the pressure dependence of the melting temperature is accurately determined for modifications I and II. Extrapolation to 1 bar yieldsdT _m/dp=43.6 K/kbar and a heat of fusionΔH _m=8.0 kJ/ mol for modification I. The values for modification II are 21.4 and 6.9 resp. Up to 4.25 kbar data of melting temperature, volume, entropy and enthalpy as a function of pressure are reported and also the compressibility of the melt. Finally the relative thermodynamic stability of the different modifications is discussed.     

Non-isothermal decomposition of anhydrous silver malonate

The non-isothermal decomposition of anhydrous disilver malonate was studied up to 300°C by means of TG, DTA and DSC techniques in different atmospheres (e.g. N₂, H₂ and air). Acetic acid, CO₂, acetone and CO were identified as the volatile decomposition products using gas chromatography. Silver metal, on the other hand, was identified as the final solid product using X-ray powder diffraction. The mechanism described involves the breakdown of adsorbed radicals, probably including-CH₂COO- and related species, on the surface of the metallic silver product. The activation energy (ΔE) and the frequency factor (InA) were calculated for the decomposition process from the variation of peak temperature (of the DTA curves) with the rate of heating (φ). The enthalpy change (ΔH), the heat capacity (C _p) and entropy change (ΔS) were calculated from the DSC measurements.