Potentiometric determination of dissociation constant and thermodynamic parameters of dissociation process of some newly synthesized pyrimidine derivatives in MeOH/DMF–water medium at different temperatures

2014 ◽  
Vol 190 ◽  
pp. 190-195 ◽  
Author(s):  
K.D. Bhesaniya ◽  
S. Baluja
e-xacta ◽  
2017 ◽  
Vol 10 (2) ◽  
pp. 73 ◽  
Author(s):  
Heloísa Righi Pessoa da Silva ◽  
Roberta Pazinato Cuco ◽  
Barbara Daniele Almeida Porciuncula ◽  
Camila Da Silva

<p>Este estudo tem como objetivo a obtenção de dados cinéticos da secagem de cenouras, bem como o ajuste de modelos matemáticos aos dados experimentais e determinação dos parâmetros termodinâmicos do processo. Buscando este propósito, experimentos foram conduzidos em estufa com renovação e circulação de ar, nas temperaturas de 50, 60, 70 e 80 °C. Os modelos matemáticos foram ajustados aos dados das cinéticas de secagem à diferentes temperaturas, e os modelos de Page e de Midilli apresentaram o maior coeficiente de correlação (R<sup>2</sup>) e menor valor de RMSE. Da análise termodinâmica verificou-se que a entalpia e a energia livre de Gibbs diminuíram com o aumento da temperatura, característico de um processo endotérmico. A entropia apresentou valores negativos e diminuiu com a diminuição na temperatura de secagem, isto indica que há um aumento no grau de ordem do sistema, considerado desfavorável entropicamente.</p><p> </p><p>ABSTRACT</p><p>This study aims to obtain kinetic data of carrot drying, as well as the adjustment of mathematical models to the experimental data and determination of the thermodynamic parameters of the process. For this purpose, experiments were conducted in an oven with renovation and circulation of air, at temperatures of 50, 60, 70 and 80 °C. The mathematical models were adjusted to the drying kinetics data at different temperatures, and the Page and de Midilli models presented the highest correlation coefficient (R<sup>2</sup>) and lowest RMSE values. From the thermodynamic analysis it was verified that the enthalpy and the free energy of Gibbs decreased with the increase of the temperature, characteristic of an endothermic process. The entropy presented negative values and decreased with the decrease in the drying temperature, this indicates that there is an increase in the degree of order of the system, considered as entropically unfavorable.</p>


2020 ◽  
Vol 16 (2) ◽  
pp. 158-165 ◽  
Author(s):  
Natalija Nakov ◽  
Katerina Brezovska ◽  
Vasil Karchev ◽  
Jelena Acevska ◽  
Aneta Dimitrovska

Background: The available data concerning aqueous dissociation constant of mupirocin (sparingly soluble drug) are scarce. In this study, chromatographic, surfactant based potentiometric concept and spectrophotometric method were used for determination of the aqueous pKa value of mupirocin. Methods: Different approaches were used for estimation of the aqueous pKa value from the apparent pKa values obtained at four ACN concentrations, ranging from 22% to 30%. The potentiometric determination of the pKa value of mupirocin was performed using different concentration of Tween 80 as a surfactant. Results: The aqueous pKa value of mupirocin, determined for the first time by reverse-phase liquid chromatography method, was found to be 4.76. The obtained value was confirmed by potentiometric method (4.85). It was found that Tween 80 increases the pKa values. The linear relationship between the apparent pKa values and the surfactant concentrations was used as an approach for estimation of the aqueous pKa value. Both methods gave similar values for aqueous pKa which correspond with the theoretically obtained pKa value (4.88) using Pallas computer program. It was found that mupirocin gives pH-indipendent spectra, thus spectrophotometric method is not applicable for determination of pKa of this compound. Conclusion: This comprehensive approach used for the pKa determination enable us to obtained reliable results for the aqueous pKa value of mupirocin. The linear relationship between the pKa values and the nonionic surfactant concentrations could be used as a reliable and simple approach for determination of aqueous pKa value of sparingly soluble drugs.


2019 ◽  
Vol 57 (9) ◽  
pp. 778-783
Author(s):  
V E Shiryaeva ◽  
A A Korolev ◽  
T P Popova ◽  
A Y Kanateva ◽  
A A Kurganov

Abstract Chromatographic determination of the thermodynamic parameters of sorption for light hydrocarbons retention on a stationary phase based on poly [trimethylsilyl (propyn-1)] (PTMSP) was performed and the effect of column preheating at temperatures up to 260°C on the retention of analytes was investigated. It was shown that heating the column to 130°C does not affect the retention of the analytes. At temperatures above 130°C, the gradual decrease of the retention of analytes on PTMSP stationary phase is observed. The process is non-selective and proceeds at the same extent for all the studied hydrocarbons, regardless of the size and geometry of the molecule. Values of enthalpy and entropy of sorption of light hydrocarbons are determined for the original column and after its aging at 200°C. The enthalpy of sorption of the analytes at the PTMSP phase is practically independent on the heating temperature of the PTMSP phase, whereas the loss of entropy increases after heating. The increase of the entropy factor after the heating of the PTMSP stationary phase is associated with its aging and is confirmed by the construction of compensation functions for treated and untreated columns.


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