Thermodynamic characterization of chromium tellurate

The standard Gibbs energy of formation of chromium tellurate, Cr₂TeO₆ was determined from the vapour pressure measurement of TeO₂(g) over the phase mixture Cr₂TeO₆(s) + Cr₂O₃(s) in the temperature range 1,183–1,293 K. A thermogravimetry (TG)-based transpiration technique was used for the vapour pressure measurement. This technique was validated by measuring the vapour pressure of CdCl₂(g) over CdCl₂(s). The temperature dependence of the vapour pressure of CdCl₂(g) could be represented as logp (Pa) (±0.02) = 12.06 ? 8616.3/T (K) (734 ? 823 K). A ‘third-law’ analysis of the vapour pressure data yielded a mean value of 185.1 ± 0.4 kJ mol^?1 for the enthalpy of sublimation of CdCl₂(s). The temperature dependence of vapour pressure of TeO₂(g) generated by the incongruent vapourisation reaction, $ {\text{Cr}}_{ 2} {\text{TeO}}_{ 6} (\rm s) \to {\text{Cr}}_{ 2} {\text{O}}_{ 3} (\rm s) + {\text{TeO}}_{ 2} (\rm g) + 1/2\,{\text{O}}_{ 2} (\rm g) $ could be represented as logp (Pa) (±0.04) = 18.57 – 21,199/T (K) (1,183 – 1,293 K). The temperature dependence of the Gibbs energy of formation of Cr₂TeO₆ could be expressed as $ \{ \Updelta G_{\text{f}}^{ \circ } ({\text{Cr}}_{ 2} {\text{TeO}}_{ 6} ,{\text{ s}}){\text{ (kJ}}\,{\text{mol}}^{ - 1} )\pm 4. 0 {\text{\} = }} - 1 6 2 5. 6 { \,+\, 0} . 5 3 3 6\,T({\text{K}}) \, (1{,}183 - 1{,}293\,{\text{K}}). $ A drop calorimeter was used for measuring the enthalpy increments of Cr₂TeO₆ in the temperature range 373–973 K. Thermodynamic functions viz., heat capacity, entropy and Gibbs energy functions of Cr₂TeO₆ were derived from the experimentally measured enthalpy increment values. $ \Updelta H_{{{\text{f}},298\,{\text{K}}}}^{ \circ } ({\text{Cr}}_{ 2} {\text{TeO}}_{ 6} ) $ was found to be ?1636.9 ± 0.8 kJ mol^?1.     

Thermodynamic characterization of carbon black-filled rubbers

Unfilled and carbon black-filled samples of synthetic isoprene- and butadiene-methylstyrenebased rubbers were characterized by precise heat capacity measurements in the temperature interval 4.2–300 K. Both unfilled samples proved to behave in an essentially fracton-like way in the temperature interval 6–30 K. The excess thermodynamic quantities derived from the smoothed data suggested that the thermodynamic state of the elastomeric phase in the filled rubbers was intrinsically unstable.     

Thermodynamic characterization of the acetylacetone-trichloroethylene system

Delfini, M., Gironi, F. and Variali, G., 1984. Thermodynamic characterization of the acetylacetone-trichloroethylene system. Fluid Phase Equilibria, 18: 69–82.Vapor-liquid equilibria have been measured for the system acetylacetone-trichloroethylene at 100, 200, 400 and 760 mm Hg. The influence of trichloroethylene on the keto-enol equilibrium of acetylacetone has been elucidated by ¹H NMR spectroscopy.A semiempirical model taking into account the “true” chemical species involved (the enol and keto tautomers of acetylacetone, and trichloroethylene) is used for thermodynamic reduction of the experimental data.     

Thermodynamic characterization of different actin isoforms

Summary The thermodynamic properties of the cardiac and skeletal a-actin isoforms were studied to characterize the molecular bases of the functional differences between them with the method of differential scanning calorimetry (DSC). The thermal properties of the actin filaments were described in the presence of calcium and magnesium ions as well. Based on the calculated free energy changes the α-cardiac actin filaments appeared to be more stable in its physiologically more relevant, magnesium saturated form. The magnesium saturated form of the α-cardiac actin filaments seemed to be more stable compared to the calcium saturated form of it. The enthalpy and entropy changes could differentiate between the α-cardiac and α-skeletal actin isoforms and between the calcium and magnesium saturated cardiac actin isoforms as well. Our results can demonstrate that the few differences between the amino acid sequences of the α-actin isoforms have an influence on the thermal properties and maybe on the function of these proteins as well.     

Thermodynamic characterization of asphaltene-resin interaction by microcalorimetry

This paper collects the work performed by isothermal titration calorimetry (ITC) to characterize the interaction between petroleum asphaltenes and resins. The interaction between these two fractions is of great interest in order to understand the mechanism of stabilization ofasphaltenes in crude oil. To simplify the approach, this preliminary study focuses on toluene solutions of both fractions. This paper reports the experimental determination of the average number of sites in asphaltene molecules and the enthalpy of interaction between asphaltenes and resins. Two models have been used to fit the experimental data. The enthalpies calculated by ITC are in the order of -2 to -4 kJ/mol. These values are in the limit of hydrogen bonding and permanent dipole energies. Similar values have been obtained by using the enthalpy as a fitting parameter in the SAFT equation.     

Thermodynamic characterization of ternary solutions of uncharged polymers

The thermodynamic interactions in aqueous solutions of uncharged polymers were studied. Using a gel-deswelling method, the water activities (chemical potentials) in binary and ternary (two polymers in one solvent) solutions of methylcellulose (MC), polyvinyl alcohol (PVA) and polyvinyl pirrolidone (PVP), respectively were determined at various polymer volume fractions (1.0 × 10⁻² < v₂ < 1.0 × 10⁻¹). On the theoretical basis of the Flory–Huggins approximations, the relevant solvent–segment (χ₁₂ or χ₁₃) and segment–segment pair interaction parameters (χ₂₃) have been calculated.

The solvent activity curves (ln a₁ versus polymer volume fraction) can be well described by a polynomial of third-degree in both the binary and the ternary solutions of the polymers. The solvent–segment interaction parameters exhibit a slight dependence on the polymer concentration. For each binary solution, the χ₁₂−v₂ function can be fitted by a straight line wich has a small positive slope. In the mixtures of two polymers, the values of the segment–segment (χ₂₃) interaction parameters were close to zero or sligthly negative (χ₂₃ 0 ± 0.03), indicating that under the studied conditions, the polymers in the ternary solutions are compatible.     

Thermodynamic characterization of polymer‐polymer interfaces

The properties of multiphase polymer blends are determined in part by the nature of the polymer‐polymer interface. The interfacial tension, γ, influences morphology development during melt mixing while interfacial thickness, λ, is related to the adhesion between the phases in the solid blend. A quantitative relation between the thermodynamic interaction energy and these interfacial properties was first proposed in the theory of Helfand and Tagami and has since been correlated with experimental measurements with varying degrees of success. This paper demonstrates that the theory and experiment can be unified for polymer pairs of some technological importance: copolymers of styrene and acrylonitrile (SAN) with poly (2, 6‐dimethyl‐1, 4‐phenylene oxide) (PPO) and with bisphenol‐A polycarbonate (PC). For each pair, the overall interaction energy was calculated using a mean‐field binary interaction model expressed in terms of the interactions between repeat unit pairs extracted from blend phase behavior. Predictions of γ and λ as a function of copolymer composition made by combining the binary interaction model with the Helfand‐Tagami theory compare favorably with experimental measurements.     

Thermodynamic and structural characterization of amphiphilic melamine-type monolayers

Monolayers of amphiphilic melamine derivatives are good candidates for the formation of supramolecular structures by hydrogen-bonding of nonsurface active species dissolved in the aqueous subphase by molecular recognition. In the present work, the thermodynamic and structural properties of the Langmuir monolayers of a homologous series of a selected amphiphilic melamine-type are characterized. Good candidates for such studies are the decyl, undecyl, and dodecyl homologues of the 2,4-di(n-alkylamino)-6-amino-1,3,5-triazine (2CnH(2n+1)-melamine) monolayers because of their two-phase coexistence region in the accessible temperature range. The characterization of the structural and phase behavior is performed by a combination of surface pressure studies with Brewster angle microscopy (BAM) imaging and Grazing incidence X-ray diffraction (GIXD) measurements. A comprehensive thermodynamic analysis provides good agreement between the experimental surface pressure - area (Pi-A) isotherms and the theoretical curves that were calculated on the basis of equations of state for a large region of monolayer stages developed by us in J. Phys. Chem. 1999, 103, 145. Theoretical curves calculated by application of equations of state only for the fluid monolayer state proposed recently by Rusanov (J. Chem Phys. 2004, 120, 10736) are in good agreement with the experiments in a limited temperature range. A rigorous equation is derived and applied to the experimental results for the calculation of the enthalpy of two-dimensional phase transition. The combination of BAM and GIXD illustrates that the microscopic long range ordering of the condensed monolayer phases is related to the lattice structure of the condensed monolayer.     

Thermodynamic characterization of polyanetholesulfonic acid and its alkaline salts

Experimental and theoretical results for the thermodynamic properties of polyanetholesulfonic acid and its lithium, sodium, and cesium salts in aqueous solution at 298 K are presented. The osmotic pressure was measured using membrane and vapor pressure apparatus in the concentration range c(m) = 0.001-0.30 monomoles/dm(3). The osmotic coefficients obtained from these measurements were low, from 0.2 to 0.45 in this concentration range, indicating a strong interaction between counterions and polyions. The osmotic coefficients of the polyacid and its lithium and sodium salts appeared to be equal within experimental error, but the results for the cesium salt were lower. This indicates a somewhat stronger binding of cesium ions to the polyanion. In addition, enthalpies of dilution, DeltaH(D), from a certain concentration, m(m), to m(m) = 0.0044 monomoles/kg were measured. The measured heats of dilution were exothermic, with the acid producing the strongest and the cesium salt the weakest effect. These results were compared with previously published data for polyelectrolytes of similar structure, namely, polystyrenesulfonic acid and its alkaline salts. The osmotic pressure results indicate that polystyrenesulfonates bind the counterions more strongly than polyanetholesulfonic acid and its salts. Consistent with this finding, the enthalpies of dilution reveal that more heat is released upon dilution of polyanetholesulfonates (stronger exothermic effect) in comparison with the corresponding solutions of polystyrenesulfonic acid in its alkaline salts. These findings can be explained in terms of the structural differences between the two polyions. The experimental results were analyzed in relation to popular electrostatic theories such as the Manning condensation theory and the Poisson-Boltzmann cell model approach, where the polyion is pictured as a uniformly charged line or cylinder. In addition, we performed Monte Carlo simulations for a model polyanetholesulfonic anion having discrete charges. In all of the calculations, the solvent was treated as a continuum with the dielectric constant of pure water under the conditions of measurement. The theoretical considerations mentioned above yield results in semiquantitative agreement with the measured quantities.     

Thermodynamic characterization of the melting of a series of polyesteramides

The changes in enthalpy, entropy and volume upon melting have been determined by dilatometric and differential scanning calorimetry measurements for four polyesteramides of the type:

$\text{-[-}\text{COφCONH(CH}{}_2\text{)}{}_{\mathrm{n}}\text{}\text{NHCOφCOO(CH}{}_2\text{)}{}_{\mathrm{m}}\text{}\text{O}\text{-]-}{}_{\mathrm{x}}$

with the following values for n and m; 6-6, 12-2, 12-6 and 12-12. The changes in each state function vary quite regularly with the number of CH₂ groups/repeating unit. A comparison is made between experimental data on the entropy of fusion and theoretical predictions. There is emphasis on the influence on the thermodynamics of melting of the rigidity of the -OCO-φ-CONH- residues and, in particular, of the persistence in the molten state of many interchain hydrogen bonds.     

Thermodynamic characterization of rare Earth salts of strong polyacid copolymers

Stoichiometric La3+, Ce3+, and Nd3+ salts of poly[(vinyl alcohol)-co-(vinyl sulfate)] (PVAS) copolymer polyacids have been studied in aqueous solution without added salt. All LnPVAS salts were entirely water-soluble in the composition and concentration range investigated. Ratios of the vinyl sulfate and vinyl alcohol units in the copolymers were between 1:5 and 1:107, leading to structural charge densities both above and under the critical value needed for counterion condensation of trivalent counterions. Solvent activity, a1, has been measured by the gel deswelling method in the concentration range of 5 x 10(-4) to 1 x 10(-1) mol of counterion/kg of water (0.2-9 w/w% of the polyelectrolyte). Results are unusually high for polyelectrolytes (-2 x 10(-6) > ln a1 > -3 x 10(-4)), and they are comparable with values determined in solutions of uncharged polymers. Nevertheless, the different copolymers can be clearly distinguished; the water activity is lowered in the order of the vinyl sulfate content of the polyelectrolytes, except for the one above the critical charge density. No observable difference was caused in the thermodynamic properties by the different lanthanide counterions. Reduced osmotic pressure curves and Flory-Huggins pair interaction parameters have been calculated; both of them were used to estimate degrees of dissociation at zero as well as at finite concentrations. Degrees of dissociation are decreasing with increasing concentration or vinyl sulfate content of the copolymer. They take values between 8-36% at zero polymer concentration and they reach zero value simultaneously at approximately 1 x 10(-3) mol of polymer chains/kg of water. The average number of released counterions per polymer chain (DPn = 1005) approaches to a limit of about 4.4 with increasing vinyl sulfate content. This corresponds to average charge distances of b > or = 19 nm and charge density parameters of xi < or = 0.037. The latter is, however, a very low value and indicates a 1/9 contraction compared to the rod-like assumption.     

Thermodynamic characterization of the binding of tetrahydropterins to phenylalanine hydroxylase

Phenylalanine hydroxylase (PAH) is the key enzyme in the catabolism of L-Phe. The natural cofactor of PAH, 6R-tetrahydrobiopterin (BH4), negatively regulates the enzyme activity in addition to being an essential cosubstrate for catalysis. The analogue 6-methyltetrahydropterin (6M-PH4) is effective in catalysis but does not regulate PAH. Here, the thermodynamics of binding of BH4 and 6M-PH4 to human PAH have been studied by isothermal titration calorimetry. At neutral pH and 25 degrees C, BH4 binds to PAH with higher affinity (Kd = 0.75 +/- 0.18 microM) than 6M-PH4 (Kd = 16.5 +/- 2.7 microM). While BH4 binding is a strongly exothermic process (DeltaH = -11.8 +/- 0.4 kcal/mol) accompanied by an entropic penalty (-TDeltaS = 3.4 +/- 0.4 kcal/mol), 6M-PH4 binding is both enthalpically (DeltaH = -3.3 +/- 0.3 kcal/mol) and entropically (-TDeltaS = -3.2 kcal/mol) driven. No significant changes in binding affinity were observed in the 5-35 degrees C temperature range for both pterins at neutral pH, but the enthalpic contribution increased with temperature rendering a heat capacity change (DeltaCp) of -357 +/- 26 cal/mol/K for BH4 and -63 +/- 12 cal/mol/K for 6M-PH4. Protons do not seem to be taken up or released upon pterin binding. Structure-based energetics calculations applied on the molecular dynamics simulated structures of the complexes suggest that in the case of BH4 binding, the conformational rearrangement of the N-terminal tail of PAH contribute with favorable enthalpic and unfavorable entropic contributions to the intrinsic thermodynamic parameters of binding. The entropic penalty is most probably associated to the reduction of conformational flexibility at the protein level and disappears for the L-Phe activated enzyme. The calculated energetic parameters aid to elucidate the molecular mechanism for cofactor recognition and the regulation of PAH by the dihydroxypropyl side chain of BH4.     

反相液相色谱中同系物收敛的热力学表征

以液相色谱中的溶质计量置换保留模型(SDM-R)为理论基础,从热力学角度进一步对反相液相色谱中同系物的收敛性进行了研究。建立了溶质平均收敛点坐标的计算方程,并从自由能变的角度表征了收敛点坐标的物理意义,阐明了收敛点的纵坐标相等的原因是溶质在收敛点处的自由能变为零。浓度收敛点的横坐标是1mol纯溶剂的解吸附自由能;而碳数收敛点的横坐标为当流动相中有机溶剂的浓度为纯有机溶剂浓度的十分之一时的同系物端基的保留自由能的负值。并以实验数据对该方程进行了验证,两者符合程度甚佳。     

Thermodynamic characterization of the amphoterism of solid oxides MO in aqueous media

Thermodynamic method was used to calculate, with account of the formation of hydroxo complexes, the molar solubilities of crystalline and amphoteric oxides MO as functions of the pH value of an aqueous-alkaline nonoxidizing medium at 25°C and constants of heterogeneous equilibria in water and alkaline and acid media for amphoteric metal MO, where M is Be, Mn-Zn, Cd, Hg, Sn, or Pb.     

Thermodynamic characterization of poly(2,2,3,3,3‐pentafluoropropyl methacrylate)

The thermodynamic characterization of a fluorinated methacrylic homopolymer was conducted by means of inverse gas chromatography (IGC), at infinite dilution. The homopolymer under study, poly(2,2,3,3,3‐pentafluoropropyl methacrylate) (PPFPMA), was synthesized via a free radical polymerization reaction and was characterized by the employment of Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and size exclusion chromatography (SEC) techniques. The specific retention volume of 15 solvents, used as probes, was used for the assessment of the Flory–Huggins interaction parameter, the weight fraction activity coefficient, the molar heat, energy and entropy of sorption, the partial heat of mixing of the probes, as well as the solubility parameter of the polymer. The results demonstrate that PPFPMA is insoluble in most organic solvents even at increased temperatures, with the exception of solvents like 2‐Butanone. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1826–1833, 2010     

Thermodynamic and structural characterization of a mixed perfluorocarbon-phospholipid ternary monolayer surfactant system

Pulmonary lung surfactant is a mixture of surfactants that reduces surface tension during respiration. Perfluorinated surfactants have potential applications for artificial lung surfactant formulations, but the interactions that exist between these compounds and phospholipids in surfactant monolayer mixtures are poorly understood. We report here, for the first time, a detailed thermodynamic and structural characterization of a minimal pulmonary lung surfactant model system that is based on a ternary phospholipid-perfluorocarbon mixture. Langmuir and Langmuir-Blodgett monolayers of binary and ternary mixtures of the surfactants 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol (DPPG) and perfluorooctadecanoic acid (C18F) have been studied in terms of miscibility, elasticity and film structure. The extent of surfactant miscibility and elasticity has been evaluated via Gibbs excess free energies of mixing and isothermal compressibilities. Film structure has been studied by a combination of atomic force microscopy and fluorescence microscopy. Combined thermodynamic and microscopy data indicate that the ternary monolayer films were fully miscible, with the mixed films being more stable than their pure individual components alone, and that film compressibility is minimally improved by the addition of perfluorocarbons to the phospholipids. The importance of these results is discussed in context of these mixtures' potential applications in pulmonary lung surfactant formulations.     

Thermodynamic characterization of microwave sintered sodium beta alumina by a potentiometric technique

The characterization of the phase equilibrium in microwave sintered sodium beta alumina was carried out by following up the variation in the sodium oxide activity on changing sodium activity in the ambience. The microwave-processed material was found to respond much faster in adapting to the surrounding atmosphere when compared to the conventionally processed materials. The results of the present investigation helped in assessing the suitability of the microwave sintered sodium beta alumina for technological applications.     

Thermodynamic characterization of binding of DNA with cisplatin in aqueous solution by calorimetry

The behaviour of cis-diamminedichloroplatinum(II) (cisplatin) binding to DNA was studied thermodynamically by calorimetric methods such as flow microcalorimetry and differential scanning calorimetry (DSC). The thermodynamic quantities of binding of cisplatin to DNA were determined from the measurement of the heat of mixing. From the results obtained, it was suggested that the complex formation by the interaction of DNA with cisplatin may be influenced by the entropy term as a dominant factor. UV spectral measurement on solutions having a known concentration of DNA and cisplatin solutions of various concentrations was carried out at room temperature, and the difference of absorption, Δ A ₂₆₀ at wavelength 260 nm between DNA solutions with and without cisplatin was estimated. From the results obtained, a hyperchromic effect in the DNA solution containing cisplatin was found to exist. The appearance of the hyperchromic effect may be considered to originate from the disturbance of the base stacking between adjacent base pairs of DNA by the interaction of DNA with cisplatin. In addition, the thermal stability of the DNA-cisplatin complex was also studied by DSC method. The binding of cisplatin decreases the thermal stability of DNA; the transition temperature and the heat of the helix-coil transition of DNA decrease accompanying the binding of cisplatin. The decrease of the transition temperature is caused by the kinked DNA(helix') accompanying the appearance of the hyperchromic effect by binding cisplatin; also, the decrease of the heat of helix-coil transition may be based on the cooperative action between the heat of helix-coil transition of the kinked DNA(helix') and the heat of dissociation when cisplatin is dissociated from the DNA-cisplatin complex. By taking into consideration these results, the heat of binding of cisplatin to DNA was estimated to be about −106 kJ per mole of cisplatin.