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Journal of Thermal Analysis and Calorimetry
Authors: G. Wolf, J. Lerchner, H. Schmidt, H. Gamsjäger, E. Königsberger, and P. Schmidt
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Abstract  

A method has been purposed to calculate some of the thermodynamic quantities for the thermal deformation of a smectite without using any basic thermodynamic data. The Hançılı (Keskin, Ankara, Turkey) bentonite containing a smectite of 88% by volume was taken as material. Thermogravimetric (TG) and differential thermal analysis (DTA) curves of the sample were obtained. Bentonite samples were heated at various temperatures between 25–900°C for the sufficient time (2 h) until to establish the thermal deformation equilibrium. Cation-exchange capacity (CEC) of heated samples was determined by using the methylene blue standard method. The CEC was used as a variable of the equilibrium. An arbitrary equilibrium constant (K a) was defined similar to chemical equilibrium constant and calculated for each temperature by using the corresponding CEC-value. The arbitrary changes in Gibbs energy (ΔG a 0) were calculated from K a-values. The real change in enthalpy (ΔH 0) and entropy (ΔS 0) was calculated from the slopes of the lnK vs. 1/T and ΔG vs. T plots, respectively. The real changes in Gibbs energy (ΔG 0) and real equilibrium constant (K) were calculated by using the ΔH 0 and ΔS 0 values. The results at the two different temperature intervals are summarized as below: ΔG 1 0H 1 0−ΔS 1 0 T=−RTlnK 1=47000−53t, (200–450°C), and ΔG 2 0H 2 0S 2 0T=−RTlnK 2=132000−164T, (500–800°C).

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Abstract  

A new adsorption isotherm equation based on the extension of the potential theory of adsorption on microporous fractal solids and corresponding thermodynamic functions were formulated and applied for description of the experimental data of adsorption on a microporous carbon. The comparison of the obtained results with the original Dubinin-Astakhov equation is presented. In this paper the dependence of thermodynamic functions (the differential molar enthalpy of adsorption ΔH and the differential molar entropy of adsorption ΔS) on the fractal dimension D are discussed, as well.

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/Δ r G ranged from 0.20 to 1.14. These differences are not trivial and are of great importance when considering the thermodynamics accompanying the “origin of life” as it is thought to occur under anaerobic conditions

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Abstract  

Enthalpies of solution and dilution of aqueous solutions of sodium diclofenac salt were measured by isoperibolic calorimeter at 293.15, 298.15, 303.15, 308.15 and 318.15 K. The concentration of the electrolyte was restricted to solubility salt at various temperatures and did not exceed 0.035–0.057 mol kg−1 values depending on the studied temperature. The virial coefficients were derived from Pitzer’s model and the excess thermodynamic functions of both the solution and the components of the solution were calculated. The analysis of thermodynamic characteristics of the solution from concentration and temperatures was carried out and discussed.

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Journal of Thermal Analysis and Calorimetry
Authors: C. Giancola, A. Buono, G. Barone, L. De Napoli, D. Montesarchio, D. Palomba, and G. Piccialli

Abstract  

In this work we report a thermodynamic characterization of stability and melting behaviour of two 24-mer DNA triplexes. The third strand, that binds the Watson-Crick double helix with Hoogsteen hydrogen bonds, contains 3′-3′ phosphodiester junction that determines the polarity inversion. The target double helix is composed of adjacent and alternate fragments of oligopurine-oligopyrimidine tracts. The two helices differ from the substitution of the cytosine, involved in the junction, with the thymine. Calorimetric data reported here provide a quantitative measure of the influence of pH and base modification on the stability of a DNA triplex.

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A theoretical description of the proton dissociation process of weak polyacids is given. Incorporation of conformational variability in the free energy of a polyelectrolyte system provides quantitative fitting of experimental data. In addition, it extends the validity of the theory to cases in which a cooperative order-disorder transition takes place. Biopolymers considered are: poly(L-aspartic acid), poly(L-glutamic acid), samples of poly(uronic acid) and some carboxylic derivatives of a gelling bacterial polysaccharide.

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