Crown ethers host-guest complexation

In this chapter we discuss host-guest complexes of arenediazonium salts with crown ethers and related compounds. Transition metal complexes of arenediazonium ions are treated together with those of dinitrogen and of diazoalkanes in our second book (Zollinger, 1995, Sec. 10.1). 

HMPT, see Hexamethylphosphoric triamide Host-guest complexation, general 289ff., 293ff., 321, see also Crown ether complexes... 

Kuhn, R., Emi, F., Bereuter, T., and Hausler, J., Chiral recognition and enantiomeric resolution based on host-guest complexation with crown ethers in capillary zone electrophoresis, Anal. Chem., 64, 2815, 1992. 

Fig. 28. Host-guest complex formed between ferrioxamine B (4) and 18-crown-6 crown ether an ionophore-siderophore supramolecular assembly.

Loeb has reported a series of pseudorotaxanes [84,85] and rotaxanes [86,87] where C-H- 0 hydrogen bonding interactions (together with N+- -O attractive forces) play an important contribution in templating the formation of the interlocked species. In particular, the formation of a pseudorotaxane was observed when equimolar amounts of [pyCH2CH2py]2+ and the crown ether 20 were mixed. The structural characterization of the resulting host-guest complex... 

The maximum observed free energy difference between two enantiomeric host-guest complexes in which one 1,1 -dinaphthyl element is the only source of chirality in the crown ether is about 0.3 kcal mol-1. Improvement of the free energy difference can be achieved by introduction of two such elements. Unfortunately crown ethers with three 1,1 -dinaphthyl groups did not form complexes with primary ammonium salts (de Jong et al., 1975). The dilocular chiral crown ether [294] forms complexes of different stability with R- and 5-cr-phenylethylammonium hexafluorophosphate. The (J )-J J -[284] complex was the more stable by 0.3 kcal mol-1 at 0°C (EDC value 1.77) (Kyba et al., 1973b). Crown ether [284] also discriminates between the two enantiomers of phenylglycine methyl ester hexafluorophosphate and valine methyl ester... 

Host-guest inclusion complexes, 262—263 antibiotic hosts, 231—233 cahxarene hosts, 228—231 chiral crown ether hosts, 213—218 cyclic oligosaccharide hosts, 218—222 cyclodextrin host selectivities, 223/ host molecular size, 221 hnear ohgosaccharide hosts, 222—228 ir- TT stacking interactions, 217 proteic hosts, 231 Human 15-hpoxygenase, 52/... 

Crown-ethers are macrocyclic polyethers capable of forming host-guest complexes, especially with inorganic and organic cations. Modification of the crown-ether by the introduction of four carboxylic groups makes it possible to use this class of compounds as chiral selectors in CE. ... 

A molecule that contains one or more binding sites that can accommodate inorganic or organic ions referred to as guests. The binding site could even be a cavity within a crystal structure. Although enzymes clearly qualify as examples of host molecules, the term is usually restricted to structures such as crown ethers, macrocycles, and cyclodextrins. Nevertheless, these hosts do serve as models for molecular recognition. See also Crown Ethers Macrocycles Inclusion Complexes... 

HORN-BORNIG PLOT HORSERADISH PEROXIDASE HOST-GUEST INTERACTIONS HOST MOLECULE CROWN ETHERS MACROCYCLES INCLUSION COMPLEXES HOCKEL MOLECULAR-ORBITAL CALCULATIONS... 

R Kuhn, F Stoeklin, F Emi. Chiral separations by host—guest complexation with cyclodextrin and crown ether in capillary zone electrophoresis. Chromatographia 33 32—36, 1992. 

Acid hydrolysis under standard conditions (6M HC1, 110 °C, 24 h) leads to partial decomposition of selenocystine and selenocysteine derivatives, thus making quantification of this amino acid by amino acid analysis difficult. Similarly, acid hydrolysis of 5e-[2-(4-pyr-idinyl)ethyl]selenocysteine peptides, obtained by reduction of the selenocystine peptides with NaBH4 and reaction with 4-vinylpyridine, results in partial decomposition. This de-rivatization, however, is useful for the enantiomeric resolution of the acid hydrolysates by capillary zone electrophoresis by applying host-guest complexation with crown ethers.11" 22 ... 

It has been suggested that in the crown-ether complexes, crystal stability is correlated with an increase in the X—H acidity of the guest9). Bifurcated hydrogen bonds are also common in these host/guest complexes, and their occurrence has been correlated with an increase in the acidity of the X—H groups10>. 

Polar O—H bonds are found in molecules such as water and alcohols. Crystal structures of several crown ether complexes have indicated that the cavity need only be partially filled by water.260-262 Several host-guest complexes of alcohols with the pyridino crown (83) have been reported.263 Longer chain and branched alcohols do not in general form crystalline adducts with this ligand. 

Fig. 8. Working hypothesis for the development of pH-gated peptide structures. Specific conformations can be induced and stabilized by the formation of a side-chain host-guest complex between an ammonium group and a crown ether. (Reproduced with the permission of Ref. 11).

Schneider, H.J. Rudiger, V. Raevsky, O.A. The incremental description of host-guest complexes Free energy increments derived from hydrogen bonds applied to crown ethers and cryptands. Org. Chem. 1993, 58 (14), 3648-3653. 

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