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Anion Sensing: -/- by Franz P. Schmidtchen (auth.), Ivan Stibor (eds.)

By Franz P. Schmidtchen (auth.), Ivan Stibor (eds.)

This treatise on anion sensing and popularity represents a brand new addition to a truly small variety of books during this area......

Although this Topics volume doesn't disguise the entire diverse sessions fo receptors, it does offer new and well timed views to anion chemistry by way of highlighting numerous parts which were commonly neglected in different reports. the person chapters are well-written and contain references from prior works as much as the current. As such, this quantity might be of curiosity to the group of researchers drawn to anions in addition to to those that desire to find out about the host-guest chemistry of anion popularity and its applications.

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The enantioselective Chiral Recognition of Anions 47 transport of amino acids, facilitated by the receptors 32–34, was studied in a U-shaped tube using chloroform as a liquid membrane. The amino acid guests (Z-Ala, Z-Phe, Bz-Ala) were dissolved in cesium hydroxide. The constants of chiral recognition determined from transport ratios of the enantiomers as kL/kD are summarized in Table 3. The discrimination between enantiomers of Z-phenylalaninate was observed only using receptors 32 and 33 for the complexation.

Ligand 31 showed preferential binding of the L-enantiomer of N-Ac-Ala (K=1,610 M–1) against N-Ac-D-Ala (K=930 M–1). Also a slight preference for the L-enantiomer of N-AcTrp (K=1,145 M–1) over N-Ac-D-Trp (K= 1,005 M–1) was observed. On the contrary, the D-enantiomer of N-Ac-Phe showed preference over the L-enantiomer, (N-Ac-D-Phe: K=680 M–1; N-Ac-L-Phe: K=585 M–1). There are two problems connected with this unexpected behavior. First, the ligand is still rather flexible and second, it contains only one chiral center.

The overall conformation of the L-Trp was determined from the information provided by the NMR spectra (NOE). This conformation reduced the number of alternative docking orientations and placed the indole ring oriented toward the ester group linking the aza-crown subunit to the guanidium. The optimized structures of complexes between 14b and both the enantiomers of tryptophan were obtained (see Fig. 2). Surprisingly, the relative distances and disposition of the two anchored pairs are quite similar for both complexes.

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