Supramolecular chemistry of ditopic anion sensors and amphiphilic molecules

Abstract

Two heteroditopic electrochemical anion sensors (2d) and (3d) comprised of crown ether for cation recognition and amidoferrocene for anion complexation using diaza-18-crown-6 and p-tert-butylcalix[4]arene as scaffold have been developed. Halide binding abilities of those two receptors in the presence and absence of Na[superscript +] and K[superscript +] cations have been investigated by [superscript 1]H NMR and electrochemical techniques compared to the monotopic receptor (1). From NMR studies, the proposed receptors presented the highest selectivity for Br[superscript -] in the presence of Na[superscript +]. In addition, they can act as electrochemical sensors for CI[superscript -] in the presence of Na[superscript +] and K[superscript +]. A new amphiphilic receptor containing a macrocyclic anionic headgroup and a single alkyl chain was prepared through an efficient templated synthesis, receptor (8b). The interdependence of the aggregation behavior and the host-guest chemistry was studied. In the absence of any guest the terminus of the alkyl chain of the receptor is included inside the hydrophobic cavity of the macrocycle leading to self-assembly into micrometer-long nanotubes. The alkyl chain can be displaced by an acridizinium bromide guest, which leads to a dramatic change in aggregate size and morphology. Studies of the solubilization of nile red suggest that the resulting aggregates are micelles having a cmc of around 35 [micrometre]. These results represent one of the first examples in which specific host-guest chemistry controls the size and shape of nanoscale aggregates.