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Dissociation Enthalpies and Thermodynamic Constants of Sildenafil Citrate by the Regression of Multiwavelength pH-spectrophotometric Titration Data
Authors: Meloun Milan | Ferenčíková Zuzana | Vaverková Eva | Pekárek Tomáš
Year: 2012
Type of publication: článek v odborném periodiku
Name of source: Journal of Solution Chemistry
Publisher name: Springer
Page from-to: 2123-2137
Titles:
Language Name Abstract Keywords
cze Disociační entaplie a termodynamické disociační konstanty sildenafil citrátu regresní analýzou pH-spektrofotometrických dat Pro stanovení disociačních konstant sildenafil citrátu při různých iontových silách a teplotách 288.15 K, 298.15 K a 310.15 K bylo užito pH-spektrofotometrických dat a dva různé přístupy vyšetření dat pomocí programů SPECFIT/32 a SQUAD(84). Spolehlivost odhadů parametrů byla dokázana těsností proložení spektrálních dat. Termodynamické disociační konstanty byly stanoveny pomocí nelineární regrese užitím Debye.-Huckelovy rovnice: pKTa1= 2.79 (1), 3.03 (3) a 3.53 (1);pKTa2 = 4.97 (2), 5.23 (2) a 5.34 (1);pKTa3 = 8.14 (2), 7.93 (1) a 7.47 (1);pKTa4 = 9.47 (2), 9.30 (1) a 9.13 (4); a pKTa5= 10.73 (5), 10.75 (3) a 10.79 (5) při T = 288.15, 298.15 a 310.15 K.. V závorkách jsou uvedeny směrodatné ochylky parametrů. Nalezené parametry byly v dobré shodě s predikčním programem SPERC založeném na kvantově chemických výpočtech na základě struktury. Faktorová analzy algoritmem INDICES odhalila správný počet světloabsorbujícíh částic. Byl proveden odhad disociační entalpie a entropie pomocí van´t Hoffovi rovnice. spektrofotometrická titrace;disociační konstanty;sildenafil citrát;SPECFIT;SQUAD
eng Dissociation Enthalpies and Thermodynamic Constants of Sildenafil Citrate by the Regression of Multiwavelength pH-spectrophotometric Titration Data pH-spectrophotometric titration data were used to determine the mixed dissociation constants of sildenafil citrate at different ionic strengths I at temperatures of 288.15, 298.15 and 310.15 K, with the use of two different multiwavelength and multivariate treatments of spectral data, SPECFIT32 and SQUAD(84) nonlinear regression analyses, and INDICES factor analysis. The reliability of the dissociation constants of this drug was proven with goodness-of-fit tests of the pH-spectra. The thermodynamic dissociation constants were estimated by a nonlinear regression of (pK (a) , I) data using the Debye-Huckel equation: pKTa1= 2.79 (1), 3.03 (3) and 3.53 (1);pKTa2 = 4.97 (2), 5.23 (2) and 5.34 (1);pKTa3 = 8.14 (2), 7.93 (1) and 7.47 (1);pKTa4 = 9.47 (2), 9.30 (1) and 9.13 (4); and pKTa5= 10.73 (5), 10.75 (3) and 10.79 (5) at T = 288.15, 298.15 and 310.15 K, respectively, where the numbers in parentheses are the standard deviations in the last significant digits. Concurrently, the experimentally determined five thermodynamic dissociation constants are in a good agreement with their computational prediction of the SPARC program based on knowledge of the chemical structures. The factor analysis of spectra in the INDICES program predicts the correct number of light-absorbing components when the instrumental error is known and when the signal-to-error ratio SER is higher than 10. A rough estimation of the dissociation enthalpies Delta H (0) (kJ center dot mol(-1)) and entropies Delta S (0) (J center dot K-1 center dot mol(-1)) has been obtained from the temperature variation of the thermodynamic dissociation constants by means of the van't Hoff equation. Spectrophotometric titration; Dissociation constant; Sildenafil citrate; SPECFIT; SQUAD

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