Guest receptors

Supramolecular Compounds Designed for Host-Guest/Receptor-Substrate interactions... 

Supramolecular Compounds involving Objects Other Than Host-Guest/Receptor-Substrate Association... 

The difficulty resides in the fact that if one modifies the guest (ligand) it is possible that not only but also the host-guest (receptor, R) affinity will be modified, depending on the nature of the modification. Experiments ought to be designed in such a way as to modify K without modifying k. This task... 

Fig. 1. Schematic representation of a receptor—substrate (host—guest) complex involving cavity inclusion of the substrate and the formation of different types of weak supramolecular interactions between receptor (hatched) and substrate (dotted).

From the kinetic point of view the facts are different and the order is reverse, ie, the rigid highly preorganized spherands are slow, as contrasted with the flexible barely preorganized podands that are fast both in formation and decomposition of the receptor—substrate (host—guest) complex (20,21). 

Fig. 26. Clathrate receptor chemistry (a) a chiroselective crystalline host compound (clathrand) (b) a typical guest molecule to be included in the specified configuration and (c) the crystal stmcture of the respective clathrate (A and B denote host and C the guest species) (169).

The main supramolecular self-assembled species involved in analytical chemistry are micelles (direct and reversed), microemulsions (oil/water and water/oil), liposomes, and vesicles, Langmuir-Blodgett films composed of diphilic surfactant molecules or ions. They can form in aqueous, nonaqueous liquid media and on the surface. The other species involved in supramolecular analytical chemistry are molecules-receptors such as calixarenes, cyclodextrins, cyclophanes, cyclopeptides, crown ethers etc. Furthermore, new supramolecular host-guest systems arise due to analytical reaction or process. 

FIGURE 6-15 Schematic representation of the ion permeability modulation for cation-responsive voltammetric sensors based on negatively charged lipid membranes. Complexation of the guest cation to the phospholipid receptors causes an increase of the permeability for the anionic marker ion. (Reproduced with permission from reference 49.)... 

The main aim in host-guest chemistry is to construct molecular receptors by a self-assembly process so that such receptors could, to some extent, gain molecular recognition capability. The goal of such molecular recognition capability is to either mimic or block a biological effect caused by molecular interactions [157]. 

A polyrotaxane with a dendrimer-like structure is known [60]. Based on the observation that [3-CD and sodium deoxycholate (NaDC) 54 forms a 2 1 host guest complex in water, Tato et al. constructed hyperbranched polyrotaxanes 55 by slowly reacting triply branched receptor 53 containing P-CD and NaDC... 

Dorns RW (2000) Beyond receptor expression the influence of receptor conformation, density, and affinity in HlV-1 infection. Virology 276(2) 229-237 Dorns RW (2004) Unwelcome guests with master keys how HIV enters cells and how it can be stopped. Top HIV Med 12(4) 100-103... 

Macrocyclic receptors made up of two, four or six zinc porphyrins covalently connected have been used as hosts for di- and tetrapyridyl porphyrins, and the association constants are in the range 105-106 M-1, reflecting the cooperative multipoint interactions (84-86). These host-guest complexes have well-defined structures, like Lindsey s wheel and spoke architecture (70, Fig. 27a), and have been used to study energy and electron transfer between the chromophores. A similar host-guest complex (71, Fig. 27b) was reported by Slone and Hupp (87), but in this case the host was itself a supramolecular structure. Four 5,15-dipyridyl zinc porphyrins coordinated to four rhenium complexes form the walls of a macrocyclic molecular square. This host binds meso-tetrapyridyl and 5,15-dipyridyl porphyrins with association constants of 4 x 107 M-1 and 3 x 106 M-1 respectively. 

Figure 70 Guest-controlled assembly of PdII-linked cage-like receptors from a dynamic library generated from a Pd11 complex and two different tridentate ligands.

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