Host-guest chemistry crown ether hosts

Host-Guest Chemistry of Triheterapentalene Crown Ethers 522... 

Early Development of Host-Guest Chemistry. Pedersen s Works on Crown Ethers... 

Recently, efforts have been initiated to examine intrinsic host-guest chemistry in the solvent-free environment of a mass spectrometer. Of present interest are preliminary reports on perfluorinated hosts, crown ethers and cryptands, which are physiologically compatible and may possess important biological properties, such as the ability to carry oxygen and transport ions through membranes. Specifically, the oxygen-binding properties of... 

The host guest chemistry of crown ethers continues to be exploited for the development of new ionophores for the selective recovery of Hg(II). A novel crown ring system containing a redox switchable trithiadiazapentalene/trithiotriuret unit (17/18) allows control of Hg(II) in solvent extraction experiments between chloroform and water. The thiocar-bonyl sulfur donor sites outside the macrocycUc cavity of (18) are responsible for strong complexation and extractabiUty into chloroform. 

The construction of macrocyles containing TTF units has received considerable attention since such molecules may act as a host in host-guest chemistry. Planar derivatives containing the TTF-crown ether 971 and TTF-crown thiaether 972 have been investigated for potential use as electroactive cation sensors <2000CSR153>. 

The formation of clathrate inclusion compounds in which guest species are enclosed by channels or cages that occur in a given host lattice was first discovered in the middle of the past century Since then a large number of clathrates and solvates, found mostly by chance as by-products of research in other areas, have been characterized ". These multicomponent systems attracted however relatively little attention, and a systematic development of their chemistry was very slow. The rapid advancement of host-guest chemistry in the last two decades, since the pioneering work of Pedersen on crown ethers provided a turning point in this respect. Initially,... 

Host-guest chemistry can be applied. For example, bola molecules with crown ether heads can host ionic surfactants such as SDS such a catanionic bola/surfactant system is expected to be responsive to additional salt or specific metal ions and, in fact, the sodium ions released from the SDS can enter the cavity of the crown ether, charging the bola, so as to form ion pairs with the anionic SDS molecules. ... 

Host-guest chemistry of crown ethers with Tc has been exploited to develop supramolecular imaging probes... 

A watershed observation was reported by Pedersen in 1967 based on studies performed at DuPont Central Research. Pedersen noted that the cyclic polyether called 18-crown-6 formed remarkably tight complexes with simple cations like K. The "crown" nomenclature arose because of the shape of the complex, with six oxygens binding the cation in a characteristic macrocyclic shape (Figure 4.6). The seminal observations of Pedersen were brilliantly exploited by other workers, most notably Cram and Lehn, and these three shared the 1987 Nobel Prize in chemistry for this work. "Host-guest" chemistry was born, with the crown ether serving as a molecular host to the cationic guest. 

This stabilization was carried to extremes in work that ultimately led to the 1987 Nobel Prize in Chemistry for Charles J. Pedersen (1904—1989) of du Pont, Donald J. Cram (1919-2001) of UCLA, and Jean-Marie Lehn (b. 1939) of Universite Louis Pasteur in Strasbourg for opening the field of host-guest chemistry. Pedersen discovered that certain cyclic polyethers (the hosts) had a remarkable affinity for metal cations (the guests). Molecules were constructed whose molecular shapes created different-sized cavities into which different metal ions fit well. Because of their vaguely crown-shaped structures, these molecules came to be called crown ethers. Rgure 6.60 shows two of them. 

Huang et al. reported apseudo[l]catenane produced by a combination of pillar[5]arene and crown ether host-guest chemistry. A novel co-pillar[5]-arene, bearing two benzo-18-crown-6 units (8.48), was synthesized by a CuAAC reaction (Figure 8.8). 1,8-Diaminooctane was added as the guest molecule to thread into the pillar[5]arene cavity to form the... 

Host-guest chemistry, based on the ability of Lewis base functionalities to coordinate positively charged ions, and the crown ethers ability to trap alkaline metals developed rapidly since its... 

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. 

Pedersen, Cram and Lehn received the Nobel Prize in Chemistry in 1987 for their work on synthetic macrocyclic compounds. In their Nobel lectures, Pedersen (1988) described the discovery of crown ethers, Cram (1988) and Lehn (1988) the further development of work on new synthetic macrocycles and their host-guest properties. 

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