Cryptophanes complexes

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... 

The crystal structures of only a few well-defined cryptophane complexes were reported. The complexes cryp-tophane-COCHiClzJ cryptophane-DOCH2Cl2, and... 

Brotin, T. Devic. T. Lesage. A. Emsley, L. Collet, A. Synthesis of deuterium-labeled Cryptophane-A and investigation of Xe cryptophane complexation dynamics by ID-EXSY NMR experiments. Chem. Eur. J. 2001. 7. 1561-1573. 

Xenon. [Xe/cryptophane] complexation dynamics have been investigated by Xe one-dimensional EXSY NMR experiments. ... 

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. 

In recent time the number of water-soluble cryptophanes reported in the literature has increased substantially. The main reason for this arises from the rapid development of the xenon-cryptophane complexes aimed at designing biosensors for MRI applications. Nevertheless, it seems important to distinguish between two types of water-soluble cryptophanes. The first series of water-soluble cryptophanes are made from a cryptophane skeleton, which has been properly modified in order to significantly enhance its solubility in water. For instance, the hexa-carboxylate cryptophane 1 (Fig. 21.2), whose synthesis is reported below (Scheme 21.1), is sparingly soluble in neutral water and very soluble in basic solution (Na0H/H20). The second class of water-soluble cryptophanes is made of lipophilic cryptophane cores, which have been adequately functionalized in order to make the whole molecule soluble in water. For example, cryptophanol-A 2, when suitably substituted by hydrosoluble moiety at the phenol function, belongs to this second class of molecule (Fig. 21.2). Original cryptophane biosensors have been prepared by this way and will be described in more detail below. 

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]. 

Fig. 16. (a) Inclusion complex of a cryptophane and (b) a carceplex (carcerand inclusion complex). 

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).

Figure 6.43 X-ray crystal structure of the CHC13 complex of cryptophane-E.

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. 

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