1098-1108Novel double-armed peptido-conjugates of
calix[4]arene 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…O hydrogen bond inscribed in a 14-atom O-H…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 calix[4]arene is further stabilized through the O-H…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 –OCH3
has also been demonstrated by variable temperature NMR studies in case of the
corresponding –OCH3 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