Host-guest chemistry anion guests

Chemical transformations at the macroeyclic chromophorc of expanded porphyrins are still not known. The complexation behavior of expanded porphyrins is very different from that of nonexpanded porphinoid macrocycles. The coordination hole of the expanded porphyrins is often too big for the complexation of a single metal ion, so in fact two metal ions can be chelated. With some expanded porphyrins, anion binding is observable, a striking difference to the nonexpanded porphyrins. The complexation behavior and the host-guest chemistry of expanded porphyrins is a rapidly growing field of research. The work in this field has been reviewed. Ie f... 

Keywords Anion host Host-guest chemistry Supramolecular association ... 

A recent macrocyclic host (65) also incorporates the metal ions into the walls of the macrocycle (165). Various small tetrahedral or Y-shaped anions were observed to selectively bridge the two metal centers and a novel host-guest chemistry was proposed. However, the system acts analogously to many of the systems already discussed. 

The use of coordination compounds with peripheral hydrogen-bonding substituents in the formation of infinite one-, two-, and three-dimensional frameworks, which can be used for host/guest chemistry, has recently been reviewed by Beatty. Brammer and Rivas, on the other hand, have reviewed the hydrogen bonding in substituted ammonium salts of the tetracarbonylcobaltate(i) anion. The reader is addressed to these two papers for a detailed analysis. 

Organocopper and -silver macrocycles are also known and it would be interesting to check their molecular recognition of anions, if any. Thus, the pentameric (jU-mesityl)copper(I) derivative [21] and the tetrameric (/i-mesityl)silver(I) derivative [22] would be interesting candidates as receptors in host-guest chemistry. 

Cooperativity is also seen for anion coordination chemistry in terms of the chelate, macrocyclic and cryptate effects. However, the area has been less extensively studied than for the transition metals and supramolecular metal ion host-guest chemistry. Some examples, primarily structural with a smattering of binding constants, which illustrate the importance of cooperativity in anion coordination chemistry are provided below. 

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. ... 

In host guest chemistry, anthracene fluorophore is of special interest in both inorganic and biological systems, because of its availability, derivatization, and fluorescence sensitivity [47]. Numerous anthracene-appended calix[4]arene hosts have been developed for the fluorogenic recognition of cations and anions. 

Practically motivated, the aim was to develop methods for recovery and determination of amino acids in the context of analytical chemistry and biotechnology. Amino acids are hydrophilic compounds, which therefore are difficult targets for conventional solvent extraction. Extraction to an organic solvent may be enhanced by the addition of lipophilic cationic or anionic extractants, forming extractable complexes with amino acids, or by the use of macrocyclic compounds, which form stable hydrophobic host-guest complexes. The most popular reagents from the latter group are crown... 

Figure 3. Schematic representations of models based on charge separation for membrane potential changes induced by host-guest complexation at liquid membrane surfaces, (a) Membrane potential change induced by a cationic guest, (b) Membrane potential change induced by an anionic guest (reproduced with permission of Elsevier Science Ltd. from Comprehensive Supramolecular Chemistry, 1996, Vol. 2,p. 176).

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