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

Four tetrapropoxycalix[4]arene-5,17-dicarboxylic acids have been prepared a nd their structures investigated in solution with NMR. The diacids were fou nd to form dimers with the acid groups pinched together in a non-polar solv ent. Salt formation with a number of primary, secondary and tertiary alipha tic amines was found to profoundly influence the structure and to depend on the number of hydrogen interactions possible and the coulombic interaction s. The binding constants for a number of amines were determined by NMR titr ations. A very high binding constant was found for the natural secondary am ine (-)-ephedrine in CDCl3. When phenylazo groups were substituted in the 1 1,23-positions the titration could be followed by absorption spectroscopy i ndicating the possibility of preparing a sensor for ephedrine type molecule s based on these calix[4]arene diacids.