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.
SourceAvailable from: Loanda Cumba[Show abstract] [Hide abstract]
ABSTRACT: Recent work has reported the first electroanalytical detection of pindolol using reduced graphene oxide (RGO) modified glassy carbon electrodes [S. Smarzewska and W. Ciesielski, Anal. Methods, 2014, 6, 5038] where it was reported that the use of RGO provided significant improvements in the electroanalytical signal in comparison to a bare (unmodified) glassy carbon electrode. We demonstrate, for the first time, that the electroanalytical quantification of pindolol is actually possible using bare (unmodified) screen-printed graphite electrodes (SPEs). This paper addresses the electroanalytical determination of pindolol utilising RGO modified SPEs. Surprisingly, it is found that bare (unmodified) SPEs provide superior electrochemical signatures over that of RGO modified SPEs. Consequently the electroanalytical sensing of pindolol is explored at bare unmodified SPEs where a linear range between 0.1 μM-10.0 μM is found to be possible whilst offering a limit of detection (3σ) corresponding to 0.097 μM. This provides a convenient yet analytically sensitive method for sensing pindolol. The optimised electroanalytical protocol using the unmodified SPEs, which requires no pre-treatment (electrode polishing) or electrode modification step (such as with the use of RGO), was then further applied to the determination of pindolol in urine samples. This work demonstrates that the use of RGO modified SPEs have no significant benefits when compared to the bare (unmodified) alternative and that the RGO free electrode surface can provide electro-analytically useful performances.The Analyst 01/2015; 140(5). DOI:10.1039/c4an02005g · 3.91 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. DOI:10.1080/00319104.2013.842473 · 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. DOI:10.1021/je400397p · 2.05 Impact Factor