Chiral recognition phenomenon

An interesting phenomenon whereby achiral compounds occupy chiral cavities has been reported. Steroidal host compounds give rise to the attachment of definite chiral conformations of achiral compounds within cavities, making it possible to observe solid-state circular dichroism spectra. Gdaniec and Polonski reported this type of property for the inclusion compounds of DCA and CA with various aromatic ketones [40a] and benzil [40c], Furthermore, it is possible for the selected conformers to maintain their chiral state temporarily in solution. That is, soon after the inclusion compounds are dissolved, the chirality may be retained for some time. /V-Nitrosopiperidines were found to display this type of dynamic chiral recognition in DCA and CA inclusion compounds [40b], In this case, one can observe the decay of the circular dichroism signal after dissolution of these inclusion compounds in methanol. 

Chiral crown ethers derived from binaphthol, pentahelicene, bi-phenanthrol, and other natural precursors have been prepared in recent years. Their chiral recognition in complexation equilibria towards various primary alkylammonium and amino acids and ester salts as well as the structural requirements of this phenomenon have been investigated. The crown ethers based on 18-crown-6 structure are known to form most... 

The odors of the two enantiomeric carvones are distinctly different from each other. The presence of one or the other isomer is responsible for the characteristic odors of each oil. The difference in the odors is to be expected because the odor receptors in the nose are chiral (see essay, "Stereochemical Theory of Odor"). This phenomenon, in which a chiral receptor interacts differently with each enantiomer of a chiral compound, is called chiral recognition. 

D-sugars - and this defines the chiral, side of life. The natural consequence is that more complex large biomolecules - proteins, polysaccharides, and nucleic acids - are homochiral as well. Chiral recognition is therefore a eommon and basic phenomenon in biology. In most cases both enantiomers of a chiral molecule aet differently in living organisms. 

Results from the hrst investigation of this phenomenon are reproduced in Fig. 4, which illustrates the chiral selectivity of the enantiomers of binaphthyl phosphate (BNP) by an amino acid-based molecular micelle. This observation not only indicated that the anisotropy could actually be sensitive to chiral recognition, but led us to posit that the magnitude of the difference could be a quantitative measure of the selectivity [28]. 

A logical extension of these ideas will lead you to a recognition of the fact that a phenomenon of this type could yield species in solution which appear to behave as if they contain a chiral centre - even when they don t. We have seen pseudo enantiomeric behaviour in compounds of the type shown in Structure 6.23 (when protonated). 

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