The structural analysis of the inclusion complex of β-cyclodextrin with m-nitrophenoxyacetic acid

The inclusion complex of β-cyclodextrin with m-nitrophenoxyacetic acid was studied by single crystal X-ray diffraction, 2D NMR spectroscopy and semi-empirical methods AM1. The crystallographic study shows that two β-cyclodextrins are held together by hydrogen bonds to form head-to-head dimers. The disordered guest molecule adjusts itself to attain the most stable accommodation into the cavity in which the nitro group is located at the dimer interface while the carboxyl group is buried in the primary hydroxyl groups of β-cyclodextrin. The guest inside the cavity is disordered over two sites and exhibits mobility. Moreover, 2D NMR spectroscopy and theoretical study show the same inclusion behavior. In comparison to the inclusion complex of β-cyclodextrin with p-nitrophenoxyacetic acid, the host-guest stoichiometries are different, i.e., 2:1 for m-nitrophenoxyacetic acid and 1:1 for p-nitrophenoxyacetic acid, while the inclusion orientation and the packing pattern of the host are similar in both complexes.

The inclusion behavior of β-cyclodextrin with m-nitrophenoxyacetic acid shows that β-cyclodextrin forms a 2:1 complex with m-nitrophenoxyacetic acid, in which the disordered guest molecule adjusts itself to attain the most stable accommodation into the cavity. In comparison to the inclusion complex of β-cyclodextrin with p-nitrophenoxyacetic acid, the host-guest stoichiometries are different, i.e., 2:1 for m-nitrophenoxyacetic acid and 1:1 for p-nitrophenoxyacetic acid, while the inclusion orientation and the packing pattern of the host are similar in both complexes.Figure optionsDownload as PowerPoint slide