Cyclophanes cyclophane receptors

While the previous receptors are typically used in organic solvents, except for the cyclodextrins, there are special cases of cyclophane receptors supphed with peripheral charges (ammonium units) (107—12) or ionizable groups (carboxylate functions) (113,114) (Fig. 17) to allow substrate recognition, as in nature, in an aqueous medium, profiting from the solvophobic effects of water (115). 

The apparent binding constant K y obtained by Stern-Volmer quenching studies is the product of the number of receptors visited by the exciton and the binding constant of to the cyclophane receptor. For this reason polymer 3 and its monoreceptor model 2 were designed so that the binding constant for methyl viologen to the receptor was known for both systems. This allowed the calculation of the true amplification factor of 67. 

Heterotopic Coreceptors — Cyclophane Receptors, Amphiphilic Receptors, Large Molecular Cages... 

The medium may have a marked effect on the shape of receptor molecules itself. Shape modifications could strongly influence their substrate binding properties, for instance in the case of amphiphilic cyclophane receptors subjected to hydrophobic-hydrophilic factors in aqueous solution. Such medium effects in action are visualized by the solid state structures of two different forms of the water-soluble hexasodium salt of the macrobicyclic cyclophane 66, which could be crystallized in two very different shapes an inflated cage structure 71 building up cylinders disposed in a hexagonal array and a flattened structure 72 stacked in molecular layers separated by aqueous layers in a lamellar arrangement [4.73]. These two... 

A macrobicyclic thiazolium cyclophane 84 functions as a model of thiamine pyrophosphate-dependent ligases and effects benzoin condensations [5.38, 5.65a, A.l 1], Acyl transfer is catalysed by formation of a ternary complex between a cyclophane receptor and two substrates [5.65b]. 

Farthing also reported the synthesis of compound 6.8 Advancements in cyclophane receptor chemistry came in 1955, when Stetter and Roos recognized the ability of cyclophanes to form inclusion complexes. They reported what they thought to be cavity inclusion complexation of benzene in cyclophane 7.9 This opened the door to the study of inclusion complexation with cyclophanes. However, in the early 1980 s when the crystal structure of Stetter s complex was solved it was shown that the benzene was located between two host molecules and not inside the... 

A water-soluble cyclophane receptor (Figure 58) has been reported to form intracavity complexes with adenine derivatives with association constants of the order of 100 M [81]. 

Figure 58 A water-soluble cyclophane receptor for adenine derivatives [811...

A basket-shaped, macrotricyclic cyclophane receptor with a deep cavity (Figure 72) has been utilized by Meric et al. for binding quaternary ammonium cations [98]. Association constants of the order of 10 -10 M were reported. 

A boxlike cyclophane receptor has been reported to complex p-nitrophenol with an association constant greater than 4 x 10 M in CDCI3 (Figure 82) [108], Large Ag values were observed in solvents such as chloroform and tetrachloroethane, whereas smaller solvent molecules such as CD2CI2 and 1,2-dichloroethane lowered the binding. A similar effect was earlier reported by Chapman and Still [109]. 

Figure 10.3. Cyclophane receptor consisting of a 4,4 -bipyridinium- and a dipeptide fragment [46],...

Poly(phenylene-ethynylene)s with cyclophane receptors as molecular wires [32]... 

Droz, A.S. Neidlein. U. Anderson, S. Seiler, P. Diederich, F. Optically active cyclophane receptors for mono- and disaccharides The role of bidentate ionic hydrogen bonding in carbohydrate recognition. Hclv. Chim. Acta 2001, 84 (8), 2243-2289. 

Fig. 5 Typical cyclophane receptors for metal ion complexation (siderophore 31. torand 32, crown ether 36), onium ion-rt interactions (33, crpptophane 38). hydrogen bonding interactions (34-37), and chiral recognition (36-38). Self-assembled cyclophanes 39 and 40.

Diederich. F. Molecular Recognition with Cyclophane Receptors in Aqueous Solution. In Modem Cyclophane Chemistry Hopf H.. Gleiter. R., Eds. in press. 

Over the last 10 years or so, numerous books (Dieder-ich and Vogtle are particularly recommended) and chapters in books were published, covering many aspects of cyclophane chemistry. Readers are pointed to a recent review on " Synthetic Receptors that also embraces many aspects of cyclophane chemistry. It is the intention of this article in the Encyclopedia to focus on more recent developments toward the end of the last century and the turn of the new millennium. The examples chosen are in no way exhaustive but rather serve as pertinent examples to emphasize the types of cavities the cyclophane receptors possess and interactions that drive complexation. Where possible, the bioinimetic nature of the receptors will be discussed because the ultimate goal in much of cyclophane work is to mimic nature s processes. It is hoped that the reader will see the cross-fertilization of cyclophane chemistry and how examples discussed in other articles on. for example, cyclodextrins, cryptophanes. cavitands, crown ethers, etc., are just as relevant to this article. 

Becher, J. A pyiTolo-tetrathiafulvalene cage Synthesis and X-ray crystal structure. Org. Lett. 2802. 4. 4189-4192. Bartoli, S. Roelens. S. Binding acetylcholine and tetra-methylammonium to a cyclophane receptor Anion s contribution to the cation-jt interaction. J. Am. Chem. Soc. 2002. 124. 8307-8315. 

The tightly bonded inclusion complexes in aqueous solution, between aromatic and aliphatic guests (steroids, among others) and cyclophane receptors with tetra-oxa[ .l.n.l]paracyclophanes and quaternary ammonium cyclophanes is entropically unfavorable and strongly enthalpically driven. The thermodynamic characteristics of tight inclusion complexes differ from those measured for weak apolar association processes, which are characterized by small enthalpic changes and favorable entropic terms. This is the usual interpretation of the so-called hydrophobic effect. 

Carcanague, D.R. Knobler, C.B. Diedrich. F. Water-soluble cyclophane receptors with convergent functional groups. J. Am. Chem. Soc. 1992. 114. 1515-1517. 

In most cases these receptors were amphfied from libraries designed to include among their members some compounds that resemble previously known receptors for the templates used. Such is the case for a series of macrocychc receptors 25,26, and 28 developed by Otto and Sanders (Scheme 3.13). These receptors were identified from amphfications observed in DCLs prepared from building blocks 22, 23, and 61 inspired by the successful cyclophane receptor 62, developed by the... 

Shipway AN, Lahav M, Blonder R, WiUner I (1999) Bis-bipyridinium cyclophane receptor- Au neuioparticle superstructures for electrochemical sensing applications. Chem Mater 11 13-15 Shipway AN, Katz E, WiUner 1 (2000) Nanoparticle arrays on surfaces for electronic, opticeil, and sensor applications. Chemphyschem 1 18-52... 

Additional evidence supporting the key role played by the size cavity in ATP hydrolysis was provided by Garcfa-Espana and coworkers for a series of cyclophane receptors 103-105 (Scheme 29). ... 

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