Abstract: Calixarenes often serve as molecular host in supramolecular chemistry, however, they show a conformation flexibility due to the inversion of the aromatic rings. It is important to control the structure flexibility of calixarenes. In this work, a C_3v-symmetrical molecular receptor calixTPA was synthesized and characterized via ¹H NMR, ¹³C NMR, ESI-MS, and X-ray structural analysis. Molecular recognitions of calixTPA for small organic ammoniums were investigated with ¹H NMR, and the inclusions of the straight chain ammoniums were reversiblly controlled by the acidity of the solution. The results indicate that the introduction of a tripodal N4-crypto cap is beneficial to rigidify the structure in a cone conformation, the hydrophobic cavity is an efficient receptor for organic guests, and the reversible recognition of straight chain ammoniums can be potentially applied in separation of organic amines.

Key words: Calixarene, Molecular recognition, ¹H NMR spectrum, Supramolecular chemistry