Zwitterionic receptors

Faced with the challenge of ion pair binding, there are three basic ion pair receptor designs contact ion pair receptors (including cascade complexes) in which the anion and cation are bound as a contact ion pair, ditopic receptors with individual, well-separated anion and cation binding sites, and zwitterion receptors, Figure 5.2. We will discuss some examples of each type of complex in the following sections. 

Figure 5.2 Schematic diagram of the three different types of simultaneous ion pair receptors, (a) cascade receptor, (b) ditopic receptor and (c) zwitterion receptor.

Guanidium-Based Anion Receptors, p. 615 Hydrogen Bonding, p. 658 Hydrophobic Effects, p. 673 Molecular Clefts and Tweezers, p. 887 Porphyrin Derivatives, Functional, p. 1139 Steroid-Based Anion Complexation Agents, p. 1365 Troeger s Base Derivatives, p. 15 6 Zwitterion Receptors, p. 1639... 

Selectivity Thermodynamic and Kinetic, p. 1225 Self-Assembly Definition and Kinetic and Thermodynamic Considemtions, p. 1248 Solvent Effects in Guest Binding, p. 1322 Spherands, p. 1344 Zwitterion Receptors, p. 1639... 

Supramolecular Electrochemistjy, p. 1412 Supramolecular Photochemistn, p. 1434 Torands, p. 1508 Zwitterion Receptor ., p. 1639... 

Zwitterionic receptors can be split into three classes (i) those that incorporate charge complementarity between the receptor and the zwitterions (ii) those in which the receptor binds one of fhe ionic parts of the substrate, which in turn causes a structural change (induced-fit) such that the other ion group then binds and (iii) betain receptors. Detains, for example, dioctanoyl-L-a-phosphaditylcholine (2.111), are nutrients that play a pivotal role in the cardiovascular system. Together with other nutrients, betains reduces the levels of toxic homocysteine (Hey) that may cause heart disease. Betains contain a tertiary trimethylammonium... 

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