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Research Article Open Access
This article is intended to combine different physico-chemical properties of three pharmaceuticals (Phs): Methoxyphenamine hydrochloride, Octopamine hydrochloride and Pargyline hydrochloride. This work aimed to: Differential Scanning Calorimetry (DSC) analysis of chosen drugs; determine phase diagrams of binary systems of tested drugs with water and selected alcohols; use different mathematical models to describe the solubility equilibria curves; spectrophotometric and potentiometric determination of acidity constants of drugs in aqueous solutions; determine of the partition coefficient 1-octanol/water. All studied drugs are salts, and they have aromatic structure and functional groups, which supposed to reveal the different interaction with water and an alcohol. The solubility was determined with a dynamic method in three important solvents: water, ethanol and 1-octanol. Measurements were carried out mainly with a dynamic visual method. The UV-Vis spectrophotometric method was used in the binary system (octopamine·HCl + 1-octanol), because the solubility was very small. The obtained experimental data were correlated with the three excess molar free energy (GEx) equations: Wilson, NRTL and UNIQUAC. Tested Phs showed larger solubility in water than in alcohols, which means that they can be served to the human body in aqueous solutions. The measurements of constant acidity were made using the potentiometric and spectrophotometric (Bates–Schwarzenbach) method. Unfortunately, the pKa data for methoxyphenamine·HCl and pargyline·HCl could not be found with a spectrophotometric method. Tests of constant acidity showed, which form of drug is active at some pH and provide guidance on drug dosage. In this work the partition coefficient 1-octanol/water for tested drugs was also determined. This coefficient is a measure of the hydrophilic/hydrophobic properties of the substance. Partition coefficient was measured by using the shake flask method, which consisted in dissolved test the substance in two solvents: 1-octanol and water. The values of the partition coefficients for all studied Phs are below unity, which shows a lipophobic character of these drugs.