Different self-assembly behaviors of mono-modified β-cyclodextrin substituted by benzoic acid derivatives

Abstract

The mono-modified β-cyclodextrin derivative, 6-O-(4-aminobenzoyl)-β-cyclodextrin (1), was synthesized and characterized. We compared its self-assembling behavior with structurally related β-cyclodextrin derivative, 6-O-(4-hydroxybenzoyl)-β-cyclodextrin (2), in aqueous solution and in the solid state using NMR spectroscopy and single crystal X-ray structure analysis. The two complexes displayed different self-assembling behaviors. Complex 1 formed a head-to-tail helical columnar superstructure in which the substituent group penetrated deeply into the hydrophobic cavity of the adjacent β-cyclodextrin from the second side and aligned along the screw axis, whereas 2 exhibited a channel superstructure with a tail-to-tail dimer as the repeating motif. Further NMR studies in aqueous solution supported the result of the solid state. The influence of substituent groups on the self-assembly behavior was examined in mono-modified β-cyclodextrins by means of substituting an amino group for a hydroxyl group, which indicates that the weak intermolecular interaction is a critical factor in determining the self-assembling behavior.