Evidence of a bimodal binding between diclofenac-Na and β-cyclodextrin in solution

The complexation between diclofenac sodium and beta-cyclodextrin was investigated in solution by 1D and 2D proton NMR. The continuous variation method was used to establish the stoichiometry. The obtained results indicate that simultaneous inclusion of both rings occur giving rise to two isomeric 1: 1 complexes. The view of a bimodal binding between diclofenac sodium and beta-cyclodextrin was also supported by ROESY experiments. The association constants for the two 1: 1 complexes were calculated by non-linear least-squares regression analysis, applying an iteration procedure. The geometry of the two 1: 1 complexes, according to the obtained NMR data is given.