Characterization of the Nonionic Microemulsions by EPR. I. Effect of Solubilized Drug on Nanostructure
Autor: | Nissim Garti, Shoshana Rozner, Maria Francesca Ottaviani, Ponisseril Somasundaran, Abraham Aserin, Somil C. Mehta, Anna Kogan |
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Rok vydání: | 2008 |
Předmět: |
Nanostructure
Chemistry Electron Spin Resonance Spectroscopy Analytical chemistry Nanoparticle Buffers Surfaces Coatings and Films law.invention Dilution Excipients Microviscosity Surface-Active Agents Carbamazepine Pharmaceutical Preparations Pulmonary surfactant law Amphiphile Materials Chemistry Nanoparticles Physical chemistry Emulsions Microemulsion Physical and Theoretical Chemistry Electron paramagnetic resonance Oils |
Zdroj: | The Journal of Physical Chemistry B. 113:691-699 |
ISSN: | 1520-5207 1520-6106 |
Popis: | The effect of the solubilized model drug, carbamazepine, on the internal structure of fully dilutable nonionic microemulsions was examined for the first time using electron paramagnetic resonance (EPR). Systems containing different surfactant to oil ratios, at two different pH values (4.6 and 8.5), with continuous dilution implementing structural transformations (micellar solution-W/O-bicontinuous-O/W) were investigated. The internal order, micropolarity, and microviscosity were scrutinized utilizing pH-dependent amphiphilic probe 5-doxylstearic acid (5-DSA). In the basic environment, the probe explored the vicinity of the surfactant head region; the deeper hydrophobic region of the surfactant tails was investigated in the acidic milieu. The study demonstrated that the EPR technique enables efficient monitoring of structural changes and examination of drug influence on structure in surfactant-poor systems. Lower order and microviscosity values were obtained in surfactant-poor systems in comparison to surfactant-rich systems. The drug functioned as a spacer of the surfactant molecules or as a cosurfactant depending on the formed microemulsion structure and the surfactant to oil ratio. The structural changes, pH variation, and presence of the drug did not alter the polarity parameter, indicating that the probe most likely does not sense a water environment in any of the examined systems. Under the basic conditions, higher microviscosity and order values were obtained in comparison to those at low pH, suggesting a higher order packing of the surfactant chains near the surfactant heads. The structural changes initiated in the vicinity of the surfactant heads, therefore, are more apparent in the basic environment. The ability to control and monitor the intramicellar interactions within drug carrier systems may be of significant interest for understanding the kinetics of drug release. |
Databáze: | OpenAIRE |
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