NMR study of the inclusion complex formed between γ-cyclodextrin and TmDOTP5−

The host–guest complex formed in aqueous solution between γ-cyclodextrin (γ-CD) and the macrocyclic paramagnetic shift reagent TmDOTP5− was examined by NMR spectroscopy. Paramagnetic lanthanide-induced shifts (LIS) and spin-lattice relaxation rate enhancements in the proton resonances of γ-CD on binding of TmDOTP5− were used to define the position of the guest anion within the host cavity. A proportionality constant which relates pseudo-contact shifts induced by TmDOTP5− to the geometrical position of each ligand nucleus (previously determined from a LIS study of the TmDOTP5− complex) was used to determine a fully bound LIS value for each γ-CD proton. These values, in combination with experimental LIS data from TmDOTP5− titrations at constant γ-CD concentration, were then used to obtain the association constant for the host-guest complex (3.9–4.5 mol l−1). These constants were indicative of a weak host-guest interaction and consistent with the location of the TmDOTP5− binding site reported by the LIS values well above the center of the γ-CD cavity.