Calix[4]arene-5,17-dicarboxylic acids and their interactions with aliphatic amines. Part 1. Studies in solution

Abstract

Four tetrapropoxycalix[4]arene-5,17-dicarboxylic acids have been prepared and their structures investigated in solution with NMR. The diacids were found to form dimers with the acid groups pinched together in a non-polar solvent. Salt formation with a number of primary, secondary and tertiary aliphatic amines was found to profoundly influence the structure and to depend on the number of hydrogen interactions possible and the coulombic interactions. The binding constants for a number of amines were determined by NMR titrations. A very high binding constant was found for the natural secondary amine (−)-ephedrine in CDCl₃. When phenylazo groups were substituted in the 11,23-positions the titration could be followed by absorption spectroscopy indicating the possibility of preparing a sensor for ephedrine type molecules based on these calix[4]arene diacids.