Inclusion behaviour of benzoic acid towards intercalates of α- and γ-zirconium hydrogen phosphates with 2-aminopropylamino-substituted β-cyclodextrin

The inclusion behaviour of benzoic acid towards intercalates of - and -zirconium hydrogen phosphates with mono[6-(2-aminopropylamino)-6-deoxy]--cyclodextrin (CDpn) has been studied at 25°C. Both intercalates take up benzoic acid to form a complex, with an accompanying partial release of CDpn. It is concluded that the remaining CDpn molecules in the -complex are rearranged as a bilayer with their cavity axes perpendicular to the phosphate layers. Those in the -complex act as a molecular prop to maintain the initial structure in which the CDpn molecules are arranged as a bilayer with their cavity axes parallel to the phosphate layers. The benzoic acid molecules are embedded inside and outside the CDpn cavity. The pore volume between the CDpn molecules amounts to approximately 0.07 and 0.29 cm³ per gram of the - and -complexes, respectively.