Reverse micellar mobile phases based on poly(oxyethylene) (4) lauryl ether (Brij 30) and sodium bis(2-ethylhexyl) sulfosuccinate (AOT) were used as mobile phases in HPLC. The chromatographic behavior of the model compounds was studied on the basis of reverse micellar mobile phases modified by salt additives. The binding of o-nitroaniline (o-NA) to the micelles of Brij 30 was determined by UVvisible spectroscopy. The different influences of kosmotropic and chaotropic anions on the binding constant K b was revealed. This may be controlled by the different arrangement of kosmotropic and chaotropic ions in the water core of reverse micelles.Reverse micelles represent one of the normal membranous structures in cells. The biological processes occurring in a reverse micellar system mimic the membranous environment. Reverse micelles are isolated, surfactant-coated water droplets, which have arisen as an appropriate model for confined water in biological systems.1 The structure of water is the subject of basic studies in physics, chemistry, and biology. The complexity of the water structure becomes enormous when it is confined to nanometer-scale cavities. Such environments include biological molecules and membranes, porous rocks and clays, and zeolites. Therefore, investigation of the properties of water core of the reverse micelles is urgent and topical. 1,2 Ion additives significantly influence the structure of a water core in the preparation of a reverse microemulsion from oil, surfactant, and water. Ions are classified as kosmotropes (structure makers) or chaotropes (structure breakers) according to their abilities to affect the structure of water. The ionic kosmotropic and chaotropic additives influence the water structure in water pockets of reverse micelles because of ion water interactions.3 Kosmotropic ions are small or multiply charged ions with a high charge density. They bind water molecules in the first hydrated layer, and they are considered to influence the water structure. Chaotropic ions are large singly charged ions with a low charge density. They retain water molecules weakly in the second hydrated layer and randomize the structure of the liquid water. 4 Direct and reverse microemulsions are used in HPLC for modeling the membrane structure. In particular, frequently, oilin-water microemulsions are used for the estimation of hydrophobicity of compounds with biomedical significance. Water-inoil microemulsions are used rarely despite their interesting structure. Due to the unique two-phase composition of water-inoil microemulsions, their use in HPLC as mobile phases may provide useful information about the solubilization of hydrophilic and hydrophobic compounds into the water nanocages of reverse micelles on the basis of the chromatographic retention factor (k). Sodium bis(2-ethylhexyl) sulfosuccinate (AOT) and sodium dodecyl sulfate are more common surfactants for the preparation of mobile phases in microemulsion liquid chromatography. 5,6 Absorption probe investigation in reverse micellar systems is a p...
The interaction of surface-active drugs with surfactants, used in the simulation of artificial membranes by direct and reversed micelles, mainly determines the transport of drugs in the body and the complex process of the binding to receptors. Besides, the delivery of drugs into the body via microemulsions has been successfully used to reduce the first-pass metabolism. The structure of mixed reverse microemulsions based on the ionic surfactant sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and the cationic surface active drug promethazine hydrochloride (PMT) was studied spectroscopically in the infrared and UV-visible regions, as well as using electrical conductivity and dynamic light scattering. The release profile of PMT from AOT-based microemulsions was studied using cellulose dialysis bags. The introduction of PMT additive into the water pockets of reverse AOT micelles leads to: a) an increase in free water fraction and a decrease in bound water fraction; b) changing the chromatographic retention factors of the model compounds; c) insignificant influence on the values of the binding constant of optical probe o-nitroaniline with the head groups of AOT; d) quenching of water-induced percolation in electrical conductance of reverse AOT microemulsions; e) a slight decrease in the size of water droplets at the same values of the molar ratio of water/surfactant. The release of PMT from the aqueous system obeys Fick’s law of diffusion (n = 0.4852), and the release of PMT from microemulsions is based on non-Fickian or anomalous diffusion.
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