Complex formation between cucurbit[n]urils and alkali, alkaline earth and ammonium ions in aqueous solution

The complex formation between cucurbit[5]uril, decamethylcucurbit[5]uril an d cucurbit[6]uril and alkali, alkaline earth and ammonium cations is examin ed. The solubility of these ligands is rather small in aqueous solution. In the presence of salts the solubility normally increases due to the formati on of complexes. The total concentration of the ligands can be easily measu red from the total organic carbon content of the salt solutions saturated w ith the ligand. From these results it is possible to calculate the stabilit y constants of the complexes formed even without the knowledge of the exact solubility of the ligand.