Crown ethers configuration

The combined features of structural adaptation in a specific hybrid nanospace and of a dynamic supramolecular selection process make the dynamic-site membranes, presented in the third part, of general interest for the development of a specific approach toward nanomembranes of increasing structural selectivity. From the conceptual point of view these membranes express a synergistic adaptative behavior the addition of the most suitable alkali ion drives a constitutional evolution of the membrane toward the selection and amplification of a specific transport crown-ether superstructure in the presence of the solute that promoted its generation in the first place. It embodies a constitutional selfreorganization (self-adaptation) of the membrane configuration producing an adaptative response in the presence of its solute. This is the first example of dynamic smart membranes where a solute induces the preparation of its own selective membrane. 

Cram et al. distinguish five classes of crown ethers of the dilocular type (I-V) and arrive at the following conclusions (Peacock et al., 1978) about the configurational preference ... 

With regard to the chiral recognition by crown ethers D. J. Cram kindly informed us that the EDC value of 38 (footnote b, Table 67) proved to be in error, and that the reported RR-S configuration in Table 68, footnote d and page 403, is still uncertain. Recent work (Peacock et al., 1980) has shown that the chiral recognition of amino acids (page 397 and Table 69) is comparable to that of amino-acid esters. The peculiar optimum in EDC values as a function of acetonitrile concentration (page 401 and Table 72) could not be duplicated. 

AZT from the corresponding mesylate by Schreiber and Ikemoto (equation 5)34. Using 3 equivalents of KO2 and 2.5 equivalents of crown ether in DMF at 0 °C for 30 min, the hydroperoxide could be synthesized in 66% yield with inversion of configuration. 

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