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    Determination of dissociation constant of naproxen in different solvent mixtures
    (Tabriz University of Medical Sciences, Faculty of Pharmacy, 2020) Asadi Ghorbani, Mahya; Mirzaei, Zeinab; Jouyban, Abolghasem; Khandar, Aliakbar
    Introduction: The dissociation constant is an important parameter in determining the behavior of compounds in various applications. Simplicity, accuracy and reproducibility of potentiometry made this method as an accepted technique for determination of dissociation constants among different methods. Aim: The aim of this project was to determine the dissociation constant of naproxen in mixtures of 1-propanol + water, 2-propanol + water and tetrahydrofuran + water in various concentrations of (10-90), (20-80), (30-70), (40-60), (50-50), (60-40), (70-30) and (80-20)% v/v at four temperatures of 298, 303, 308 and 313 K by potentiometry method using the BEST computer program. Methods: The ionic strength of solution was adjusted using potassium chloride at 0.1 mol.L-1. Naproxen titrations in different mixtures: 1-propaneol + water, 2-propaneol + water and tetrahydrofuran + water at four different temperatures of 298, 303, 308 and 313 K were done as described by Martell and Motekaitis. In order to the evaluation of the dissociation constant of naproxen, eight sample solutions in different binary solvent mixtures from 10 to 80% (v/v) were used in and the pH range of 2–12 adjusted with HCl of 0.001 mol.L-1. Results: The results showed that in different mixtures of solvents, the dissociation constant of naproxen increased with increasing the amount of organic solvent due to the dominance of the electrostatic forces in the equilibrium process and decreased by temperature increasing, because the acidity of naproxen decreases. Conclusion: The effect of temperature on the dissociation constant in three different temperatures was investigated and the related thermodynamic parameters of naproxen (ΔG°, ΔH° and ΔS°) were calculated from temperature dependence data.
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    Study of solubility and thermodynamic properties of amlodipine besylate in binary mixtures of n-methylpyrrolidone, 1-propanol, 2-propanol at different temperatures
    (Tabriz University of Medical Sciences, School of Pharmacy, 2025) Naghavi Kalajahi, Seyed Mahdi; Jouyban, Abolghasem; Rahimpour, Elaheh
    Introduction: Solubility data has extensive applications in various industries for purpose of dissolution, formulation, and crystallization processes. Various methods exist for altering drug solubility. Cosolvency is recognized as one of the simpler and more effective methods in this field. Objective: The aim of this research is to investigate the solubility and thermodynamic properties of amlodipine besylate in binary mixtures of (N-methylpyrrolidone + 1-propanol), and (N-methylpyrrolidone + 2-propanol) at different temperatures, and to predict solubility data using cosolvency models. Methods: In this study, the shake-flask method was employed for measurement of amlodipine besylate solubility in binary mixtures of solvents. In this process, an excess amount of the drug is added to vessels containing different compositions of solvents. After the solution reaches equilibrium at the specific temperature, the supernatant is separated from the remaining solid material using centrifugation or filtration. Then, after appropriate dilution, UV absorbance of the solution is measured at the drug's maximum wavelength, and the concentration of the samples are determined based on the calibration curve and dilution factors. Then, all acquired data are fitted to mathematical cosolvency models. The thermodynamic properties for dissolution and mixing are calculated using Gibbs and van’t Hoff equations. Results: The obtained data indicates that the solubility of amlodipine besylate increases with an increase in the mass fraction of the cosolvent (N-methylpyrrolidone) and with temperature increase. In both solvent-cosolvent systems, the highest solubility is observed in pure N-methylpyrrolidone at 313.2 K and, the lowest solubility in both systems is observed in pure 1-propanol and 2-propanol, respectively, at 298.2 K. Discussion and Conclusion: The present study demonstrated that with increasing temperature and increasing mass fraction of N-methylpyrrolidone, the dissolution of amlodipine besylate increases significantly. Additionally, the experimental data were compared with calculated data from various cosolvency models, and satisfactory results were obtained modeling accuracy.