Counterion neutralization, hydrogen bonds

Another way of avoiding the problems of pH range and counterion competition is to use a neutral hydrogen-bonding receptor based on amide functionalities. Peptide groups from the protein backbone are, of course, well known to be involved in enzyme anion binding as discussed earlier. Amide involve-... 

The most popular classification of surfactants is based on its ionic characteristics they are either anionic, cationic, or nonionic. Since ions are normally found in aqueous fluids, ionic characteristics of surfactants are found in the hydrophilic head thus, an anionic surfactant would have negatively charged species in the hydrophilic heads. Because of the requirement of charge neutrality in an overall fluid system, an anionic surfactant would have its positive counterion within its vicinity. This counterion is subject to various ion-exchange mechanisms either with other types of counterions in the fluid or on solid surfaces. It is possible for nonionic species to be hydrophilic, because of their polar and hydrogen-bonding interactions with water molecules. 

In both cation and anion exchangers, the acid or base groups are chemically bonded to the resin matrix, and the resins have a high concentration of fixed negative or positive ions. These are balanced by mobile counterions such as Na+, H+, or Ca2+ for cation resins and CL, OH", or N03 for anion resins, so that electrical neutrality is always maintained in the resin particles. Ion exchange takes place when the activity of ions in the external solution differs from that of the mobile ions in the solid phase. For example, exposing a hydrogen-form resin HR to a solution with Na+ and H+ will result in diffusion of some Na+ ions into the resin and diffusion of some H+ ions into the solution. 

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