Calix arenes fixation

In order to obtain more information about the factors that influence the ratios of the conformations and the interconversion process we investigated the properties of partially fixed calix[4]arenes. Using different methods for selective functionalization, we synthesized a series of mixed diethyldimethyl ethers (17), that are partially rigidified because of the presence of the ethoxy groups [16]. The partial fixation precludes one or two of the conformations and in this way also certain pathways for interconversion are excluded. Table 1 shows the ratios of conformations of the four... 

Table V displays the sodium ion selectivity for three kinds of bridged type cal-ix[4]arene derivatives. Since the capping of the lower rim of calix[4]arene with a bridge of different length methylene groups results in the fixation of a rigid cone conformation and the change of the cavity size, the Na" " selectivity is expected to be improved.

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