SQUARAMIDO-BASED RECEPTORS - DESIGN, SYNTHESIS, AND APPLICATION TO THE RECOGNITION OF TETRAALKYLAMMONIUM COMPOUNDS

A new series of tripodal receptors based on squaramido rings as unprec edented binding units has been devised. Among the different structural possibilities that this functionality offers, the ability of establis hing multiple O to C-H interactions has been explored. On this basis, new receptors capable of recognizing choline, acetylcholine, and relat ed ammonium salts have been synthesized. Association constants in the range 10(3)-10(4) M(-1) have been measured by a H-1-NMR titration meth od The formation of intracavity complexes is supported by the observat ion of characteristic changes in the NMR spectra of the complexes, of intermolecular cross peaks in 2D. ROESY experiments, and by detection of signals corresponding to the molecular weight of the complexes by p ositive FAB mass spectrometry.