The structure of inclusion complex of β-cyclodextrin with p-nitrophenoxyacetic acid in solution and the solid state

Abstract

The inclusion complex (1) of with β-cyclodextrin-p-nitrophenoxyacetic acid was synthesized and characterized. Its inclusion behavior was investigated by means of X-ray crystallography and NMR spectroscopy in solution and in the solid state. The crystallographic study shows that one β-cyclodextrin co-crystallize with one p-nitrophenoxyacetic acid, and 17 water molecules in the Monoclinic system with unit cell constants: a = 18.6864(16), b = 24.961(2), c = 16.6644(14) A, β = 105.129(5)°. Two β-cyclodextrins are held together by hydrogen bonds to form head-to-head dimers. The disordered guest molecule molulates 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 buried in the primary hydroxyl groups of β-CD. The further 2D NMR spectroscopy investigation in solution supports the inclusion mode of the solid state. The inclusion behavior of β-CD with p-NPOAA shows that β-CD forms a 1:1 complex with p-NPOAA, in which the nitro group of guest is located at the second hydroxyl groups and the carboxyl group is buried in the primary hydroxyl groups of β-CD.