Study of Influence of Salt Additives on Mixed Reverse Micelles via Reverse Microemulsion Chromatography and UV–visible Spectroscopy

Abstract

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...

Detection of Medium-Sized Polycyclic Aromatic Hydrocarbons via Fluorescence Energy Transfer

“…Energy transfer efficiencies observed in phosphate buffer for compound 6 were markedly decreased compared to the energy transfer efficiencies observed in PBS. Sodium is a known kosmotropic agent (26,27), meaning that it stabilizes hydrophobic interactions such as those required for cyclodextrin-independent energy transfer (28). Because the sodium content of PBS is substantially higher than that of the phosphate buffer, hydrophobic binding is strengthened under those conditions.…”