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.
- H NMR
- Host‐guest complex
- Lanthanide‐induced NMR shifts
- γ‐Cyclodextrin‐paramagnetic anion complex
ASJC Scopus subject areas
- Materials Science(all)