Determination of the Inclusion Geometry for the β-Cyclodextrin/Benzoic Acid Complex by NMR and Molecular Modeling

摘要

The inclusion complex of benzoic acid and β-CD has been studied. A 1:1 stoichiometry and an association constant of 48.5 M~(-1) were determined based on induced chemical shifts considering all possible protons presenting chemical shifts. This low constant indicates a very fast equilibrium between complexed and free substrates which, in turn, results in an averaged inclusion geometry. The reasonable agreement between the experimentally determined distance ratios (based on NOE values) and the computed geometry for the inclusion (carboxylic group pointing toward the smaller rim) is remarkable. The molecular mechanics-derived structure appears to be a very reasonable representative of the average geometry for the complex in solution.