Acid-base properties and solubility of pindolol, diazepam and chlordiazepoxide in SDS micelles.
ABSTRACT The effect of sodium dodecyl sulphate (SDS) on the acid-base properties and on the solubility of a beta-blocker (pindolol) and of two benzodiazepines (diazepam and chlordiazepoxide) has been assessed. The study was performed by potentiometric and spectrophotometric determinations of the acidity constants and by spectrophotometric evaluation of the solubilities of the pharmaceutical drugs in aqueous solution and in solutions to which was added SDS with concentrations below and above the critical micelle concentration (cmc), at 25 degrees C and at an ionic strength 0.1 M (NaCl). The effect of the organized assemblies on the pKa values was quantified by the application of two theoretical models that differ in the inclusion of ionic exchange between positively charged species in solution. These models have allowed the determination of the binding constants for drug/micelle and yielded values in good agreement with those obtained by the solubility method, and in addition provide a more detailed picture of the effect of drug charge on its partition. The results can be taken to evidence different interaction modes of the drugs with the SDS micelles.
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ABSTRACT: Spectrofluorimetric characteristics of pindolol have been investigated with the aim of using this technique for analytical determinations. Other monosubstituted indole derivatives, 4-methoxy and 5-methoxyindole, have been also studied for comparative purposes. Corrected excitation and emission wavelengths in different solvents are reported and the effect of solvent on the Stokes shifts of these compounds has been analysed using the Lippert equation. In addition, the Stokes shift of pindolol has been determined in dioxan–water solvent mixtures and the presence of specific solvent effects is discussed. The fluorescence of pindolol is pH dependent, the quantum yields determined in water are lower than those in other solvents. With respect to the sensitivity, it has been found that the detection limits in aqueous solutions are improved in the presence of β and methyl-β-cyclodextrin. Finally, a fluorimetric analysis of the interaction between pindolol and different cyclodextrins has been carried out in order to determine the apparent stability constants of the complexes and the thermodynamic parameters associated to complexation.Talanta 07/2003; 60:477-482. · 3.50 Impact Factor
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ABSTRACT: Micellisation of sodium dodecyl sulphate (SDS) was studied in the presence of hydrochloric acid (HCl) and perchloric acid (HClO4) using conductometry method. The conductivity-[SDS] plots showed abnormal profile pattern at [HCl] > 0.002 mol dm−3 and [HClO4] > 0.001 mol dm−3. Below these acid concentrations, conductivity pattern was normal, and the critical micelle concentration (CMC) values of SDS were lower in both acids than in water. At high acid concentrations, post-micellar slopes were negative. Fourier transform infrared (FTIR) analysis showed significant shifts in the bands suggesting the formation of dodecyl hydrogen sulphate by SDS at high acid concentrations. Thermodynamic parameters for SDS micellisation at low acid concentrations ([HCl] = 0.002 mol dm−3 and [HClO4] = 0.001 mol dm−3) were determined in the temperature range 15–40°C. As temperature increases, the change in enthalpy and entropy of micellisation becomes less positive, and the change in free energy of micellisation becomes increasingly negative.Physics and Chemistry of Liquids 05/2014; 52(3):388-399. · 0.52 Impact Factor
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ABSTRACT: The pKa values of ACE inhibitors captopril, cilazapril, enalapril, fosinopril, lisinopril, perindopril, quinapril, ramipril, and zofenopril were determined by potentiometry. Because to the presence of single or several ionizable groups (carboxyl, thiol, primary and secondary amino groups) these substances represent acids and ampholytes. Determinations of pKa values were performed at 25 °C and constant ionic strength of 0.1 M (NaCl), in the absence and in the presence of surfactants, anionic sodium dodecyl sulfate (SDS), cationic cetyltrimethyl ammonium bromide (CTAB), and nonionic 4-octylphenol polyethoxylate (TX 100). A computer program Hyperquad was used to derive pKa values from the data obtained by potentiometric titrations. The observed shift of pKa values from +1.90 to −1.54 pK units demonstrated a significant effect of the surfactants on ionization of ACE inhibitors. It has been observed that the carboxyl group was more susceptible to the effect of the above surfactants than the amino group. Also, among the three surfactants employed, SDS expressed the most prominent effect on acid–base equilibria. On the basis of the shifts of pKa values in the presence of the applied surfactants different ACE inhibitor–micelle interactions were suggested.Journal of Chemical & Engineering Data 08/2013; 58(9):2567–2573. · 2.05 Impact Factor