Cucurbit[5]uril, decamethylcucurbit[5]uril and cucurbit[6]uril. Synthesis,solubility and amine complex formation

A simple way to prepare cucurbit[5]uril is described. The macrocycles of th e cucurbituril type are nearly insoluble in water. The solubilities of cucu rbit[5]uril, decamethylcucurbit[5]uril and cucurbit[6]uril in hydrochloric acid, formic acid and acetic acid of different concentrations have been inv estigated. Due to the formation of complexes between cucurbit[n]urils and p rotons the solubility increases in aqueous acids. The macrocyclic ligands a re able to form complexes with several organic compounds. Thus, the complex formation of the cucurbituril macrocycles with different amines has been s tudied by means of calorimetric titrations. The reaction enthalpy gives no evidence of the formation of inclusion or exclusion complexes. H-1-NMR meas urements show that in the case of cucurbit[5]uril and cucurbit[6]uril the o rganic guest compound is included within the hydrophobic cavity. Decamethyl cucurbit[5]uril forms only exclusion complexes with organic amines. This wa s confirmed by the crystal structure of the decamethylcucurbit[5]uril-1,6-d iaminohexane complex.