Cryptophanes complexes with

Canceill, J., Lacombe, L., Collet, A., New cryptophane forming unusually stable inclusion complexes with neutral guests in a lipophilic solvent. J. Am. Chem. Soc. 1986, 108, 4230-4232. 

Xe NMR spectra for a xenon layer frozen on EtOH or H20/EtOH were used to obtain time-resolve imaging of melting and dissociation processes.682 129Xe NMR spectra gave information on the interaction of xenon with a dissymmetrical cryptophane ((Xe)2 bis-cryptophane) complex.683... 

Figure 11. Cryptophane-A (23) and its complexes with Xe (46). Biotinylated cryptophan-A (24) for binding to proteins (47). [Adapted from (3a).]...

A further example of a tailor-made host compound is cryptophane (162) By use of this cyclophane derived from the triveratrylene skeleton and having a large cavity inside the molecule, the differentiation of bromochlorofluoromethane (136) was successfully carried out on an analytical scale. Bromochlorofluoromethane has also been optically enriched through complexation with brucine... 

E0Me4N complex in (CD2Cl2)2- Lower association constants are attributable to the hydrophilic nature of the small aikyl ammonium cations. As the size of an alkyl ammonium ion is increased, however, it tends to become more hydrophobic. Thus, the larger cryptophane-03 forms a complex with acetylcholine that is of comparable stability to that of acetylcholine esterase. 

An interesting example of the interplay between solid-state clathrands and solution-phase cavitands is provided by cyclotriveratrylene (CTV, 8). In the solid state, the saucer-shaped CTV molecules stack one on top of another in the two most common phases (x and and hence, while the molecules possess shallow molecular cavities, they do not include guests such as solvent molecules, which instead are located in voids between host stacks. However, larger guests such as buckminsterfuller-ene C6o, organometallic sandwich compounds,or carboranes form intracavity inclusion compounds, and the association persists in the solid state, with potential applications, for example, in the selective purification of fullerenes. Thus, CTV is both a cavitand and a clathrand. The cavitand behavior of CTV is highlighted by the chemistry of the double-CTV cryptophanes that form very stable solution complexes with a variety of halocarbon guests. 

Figure 5 Crystal structures of guests within cryptophanes. (a) CHCI3 n cryptophane-E with disordered CHCI3 shown in ball-and-stick mode (b) complex (dimethyldiazapyrenium)(CH3CN)2 n 27. Guests shown in space-filling mode with dimethyldiazapyrenium in purple and CH3CN in green.

This review is dedicated to the synthesis of water-soluble cryptophanes and of the closely related hemicryptophane derivatives that were developed more recently. The study of their binding properties with different species and some peculiar properties related to their chiral structure are also described. A particular attention is given to xenon-cryptophane complexes since, as above mentioned, these complexes have played a major role in the development of water-soluble cryptophane derivatives. We describe in a concise manner the different approaches, which have been reported in the literature to introduce hydrophilic moieties onto the cryptophane structure. Finally, we report some physical properties of the water-soluble cryptophane complexes. This mainly concerns the study of their binding properties with neutral molecules or charged species. The preparation of enantiopure cryptophanes has also contributed to the development of this field. Indeed, it was stressed that cryptophanes exhibit remarkable chiroptical and binding properties in water [11]. These properties are also described. The last part of this review is devoted to hemicryptophane derivatives, which are closely related to the cryptophane structure and which allow the functionalization of the inner space of the molecular cavity. These show a renewed interest in their applications in chiral recognition and supramolecular catalysis. 

Cryptophane 1 has been prepared as both a racemate and optically active molecule, and the formation of complexes with neutral species in water has been thoroughly investigated by several spectroscopic techniques (see Sect. 21.3.2). The Xe l complex has also been used as a model system for several fundamental studies. For instance, it has been shown that the Xe chemical shift of the Xe l complex is very sensitive to a small variation in pH [14], which is characterized by a significant shift of the Xe NMR signal (Fig. 21.3). 

LP) NMR techniques at or even below the micromolar scale. For instance, compound 8 has been used to demonstrate that the xenon in-out exchange process with 8 occurs via a degenerate process [18]. Schroder et al. also reported the study of Xe 8 as a sensor to study membrane fluidity and membrane composition [19,20]. Independently, Frechet et al. demonstrated that the introduction of several Xe 8 cryptophane complexes inside a PAMAM dendritic structure allowed a significant gain (by a factor 8) in sensitivity of the Xe NMR signal [21]. 

CONTENTS Preface. George W. Gokel. Cryptophanes Receptors for Tetrahedral Molecules, Andre Collett, Jean-Pierre Dutasta and Benedict Lozach. Inclusion Polymerization in Steroidal Canal Complexes, Kiichi Takemoto, Mikiji Miyata. Functionalized Tetraazamacrocycles Ligands with Many Aspects, Thomas A. Kaden. Calixarenes as the Third Supramolecular Host, Seiji Shinkai, Kyushu University, Japan. Fluorescent Chemosensors for Metal and Non-Metal Ions in Aqueous Solutions Based on the Chief Paradigm, Anthony W. Czamik. Index. 

Figure 6.42 Complexation free energy of cryptophane-C and -E for various guests at 300 K (reproduced with kind permission from Springer Science + Business Media from Section Key Reference 1993).

---