Calixarenes host-guest inclusion

It should be stressed that there is not alwaysjustice in reseach evaluation. The selective formation of inclusion complexes by cyclodextrins (such as 11) was established by Cramer [6] at least 15 years earlier than that by crown ethers. However, cyclodextrin studies forming an independent branch of host-guest chemistry seem underestimated in spite of their considerably greater practical importance at present than that of other host macrocycles (crown ethers 17, calixarenes 18, etc.). Sometimes they are even totally neglected by discussing inclusion phenomena [7]. 

A Versatile Class of Macrocyclic Compounds, J. Vicens, V. Bohmer, Eds., Kluwer, Dordrecht, 1991, p. 65 G. D. Andreetti, F. Ugozzoli, Inclusion Properties and Host-Guest Interactions of Calixarenes in the Solid State, ibid., p. 87. 

Cavilaics include crown rnacroring inclusion compounds (coronates), cryptates, podates. cytlophane host inclusion compnunds. calixarene inclusion compounds, cyclodextrin and amylose inclusion compounds, cucurbituril inclusion compounds, molecular deft inclusion compounds, and anionic guest inclusion compounds. 

Only few investigations have been published on the gas-phase ion chemistry of host-guest complexes of calixarenes. With the advent of ESI mass spectrometry, especially when combined with ion-trap and FT-ICR mass spectrometry, this field has started to be developed. Binding selectivities of alkali metal ions to cahxarene-based crown ethers and open-chain ethers have been studied , the inclusion of neutral guests into the protonated resorcarene-based cavitand hosts by gas-phase ion-molecule reactions with amines have been studied and the formation of capsules from various calixarene tetraether derivatives and alkylammonium ions as ionic guests (notably enabling their detection by mass spectrometry) have been described recently . ... 

Single molecule force spectroscopy was used to measure the inclusion of a guest into a calixarene host molecule, which served as example in the paragraph on single molecule force spectroscopy in this chapter (see Fig. 10.23) [96]. 

The calixarenes have a flexible or rigid cavity, resp., which can be shaped to some extent. Some inclusion compounds in the solid state have bren described, but the low solubility in water did not allow applications in respect to an enzyme mimick as yet. Host/guest interactions in solution according to studies of Gutsche et al. seem to occur in some cases, but are weak. Shinkai and coworkers seem recently to have overcome parts of these problems by incorporation of sulfonic add groups in this skeleton (72 and 73). 

Harrowfield, J.M. Richmond. W.R. Sobolev. A. Inclusion of quaternary ammonium compounds by calixarenes. J. Inch Phenoin. Mol. Recognit. Chem. 1994. 19. 257. Lippmann, T. Wilde. H. Pink. M. Schaefer. A. Hesse. M. Mann. G. Host-guest complexes between resorcinol-derived cal ix [4] arenas and alkyl ammonium ions. Angew. Chem. 1993, 105, 1258-1260. ... 

Amphiphilic macrocyclic host molecules have been investigated for many years. Among others, it is known that amphiphilic crown ethers, " cryptands, calixarenes, cyclodextrins, and curcubitnrils can form bilayer vesicles in aqueous solution. However, the host-guest chemistry of such host vesicles remained largely unexplored for many years. Darcy and Ravoo prepared bilayer vesicles composed entirely of amphiphilic cyclodextrin host molecules. These vesicles have a membrane that displays a high density of embedded host molecules that bind hydrophobic guest molecules such as f-butylbenzyl and adamantane derivatives. The characteristic size-selective inclusion behavior of the cyclodextrins is maintained, even when the host molecules are embedded in a hydrophobic... 

In these solid inclusion componnds, the association of host and guest components is strictly a solid state phenomenon, and the examples covered in this chapter focns almost entirely on solid inclnsion componnds of this type. However, it is relevant to note that there is also another class of inclnsion compound in which the host is a molecnle containing an appropriate cavity or binding site that can inclnde gnest molecules. Such molecular host-guest complexes generally exist as associated entities both in the solntion state and in the crystalline state, and thns the incln-sion phenomenon is not exclusively a property of the solid state. Examples of host molecules of this type are crown ethers, cyclodextrins, cryptands, and calixarenes. 

Inclusion of cationic molecules by hosts in organic solvents is also observed with other host molecules, such as crown ethers and calixarenes. Cat-ion/n and coordination interactions are the main driving forces in these complexes. However, the formation of host-guest complexes with neutral... 

Cahxarenes are one of the most interesting scaffolds for molecular recognition in host guest chemistry. The versatihty of calixarene macrocycles includes modification of their upper and lower rims, different conformation behavior, and hydrophobic cavity for the inclusion of guest molecules. The conformational preference of calixarene derivatives depends on the substitution at the upper and lower rim. Numerous attractive receptors have been developed for the detection of various guest molecules. The molecular recognition can be characterized by various... 

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