1,3-Di-peptido-conjugates of calixarene and its di-OCH(3) derivatives: Synthesis, characterization and phosphate recognition
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Novel double-armed peptido-conjugates of calixarene have been developed on the lower rim of the macrocycle. The functional group pendants exhibit conformational bend through the involvement of 11-atom N-H center dot center dot center dot O hydrogen bond inscribed in a 14-atom O-H center dot center dot center dot O interaction. As a result, only the terminal -COOR and -COOH groups are exposed to the environment, but not the amide moiety. The cone-conformation of the calixarene is further stabilized through the O-H center dot center dot center dot O interactions at the lower rim. In effect, the conjugates exhibit a binding core at the lower rim along with hydrophobic cavity formed by the enclosure of arene moieties. Conformational mobility induced by the replacement of lower rim phenolic-OH by -OCH(3) has also been demonstrated by variable temperature NMR studies in case of the corresponding - OCH(3) derivatives. Differential receptor binding characteristics of these conjugates towards phosphate are demonstrated using absorption spectroscopy. The negatively charged phosphate group is received preferentially by the carboxylic terminal over the ester terminal conjugate.
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