Hydrophobic interactions among many solutes

Membrane lipids spontaneously form extensive bimolecular sheets in aqueous solutions. The driving force for membrane formation is the hydrophobic interactions among the fatty acid tails of membrane lipids. The hydrophilic head groups interact with the aqueous medium. Lipid bilayers are cooperative structures, held together by many weak bonds. These lipid bilayers are highly impermeable to ions and most polar molecules, yet they are quite fluid, which enables them to act as a solvent for membrane proteins. 

The basic interfacial process in flotation is selective hydrophobization (or lepophiliza-tion) and hydrophilization of particulate matter. The role of the solution chemistry is very important in flotation as it is determined by the dissolution behavior of mineral particles in the aqueous solution (pulp) and subsequent dissociation, hydrolysis and precipitation of the soluble species the dissolution, association, dispersion and emulsion behavior of various flotation reagents in the pulp and interactions among reagents with both soluble and surface species of minerals. The efficiency of flotation and separation of mineral particles and consumption of reagents are thus controlled by the solution chemistry of the pulp. As other processes such as oil displacement are also governed by such interactions and in turn by the wettability of the solid surface, the study of solution chemistry of surfactant/mineral/additive systems become very important for the development of many technologies. 

CDs are oligosaccharides with characteristic toroidal molecular shapes. Their outside surfaces are hydrophilic, while their cavities are hydrophobic. CDs tend to include molecules, which fit their cavities by hydrophobic interaction. The most widely used CDs consist of six (a-CD), seven (fi-CD), or eight (y-CD) glucopyranose units. The size of the cavity differs significantly among the a-, / -, and y-CDs. Selectivity results from the inclusion of a portion of a hydro-phobic solute into the cavity. The use of CDs is especially effective for the separation of aromatic isomers and aromatic enantiomers that have the chiral center close to the aromatic ring. Many CD derivatives have been developed for increased solubility in water as well as for modifying the cavity shape that provides different selectivities from un-derivatized CDs and are commercially available. 

Additional substances (buffer additives) are often added to the buffer solution to alter selectivity and/or to improve efficiency, and the wall of the capillary may be treated to reduce adsorptive interactions with solute species. Organic solvents, surfactants, urea and chiral selectors are among the many additives that have been recommended (table 4-24). Many alter or even reverse the EOF by affecting the surface charge on the capillary wall, whilst some help to solubilize hydrophobic solutes, form ion-pairs, or minimize solute adsorption on the capillary wall. Chiral selectors enable racemic mixtures to be separated by differential interactions with the two enantiomers which affects their electrophoretic mobilities. Deactivation of the capillary wall to improve efficiency by minimizing internet ions. with solute species can be achieved by permanent chemical modification such as silylaytion or the... 

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