Molecular Binding and Assembly Behavior of β-Cyclodextrin with Piperazine and 1,4-Dioxane in Aqueous Solution and Solid State

The molecular binding behaviors of mono-[6-deoxy-6-(1-piperazinyl)]-β-cyclodextrin (1), piperazine/β-cyclodextrin complex (2), and dioxane/β-cyclodextrin complex (3) were systematically investigated by NMR spectroscopy, mass spectrometry, dynamic light scattering, viscosity measurements, microcalorimetry, crystallography, and electron microscopic observations, displaying that the self-aggregation of piperazine-modified cyclodextrin 1 in both aqueous solution and the solid state produced a head-to-tail polymeric helical structure. In contrast, the cyclodextrin units in piperazine/β-cyclodextrin complex 2 were located in a staggered pattern, which was strikingly distinctive from the reported results by slow solvent evaporation method. Despite the fact that piperazinyl moiety was introduced by covalent and noncovalent chemical bonds in compound 1 and complex 2, respectively, these two superstructures have the same crystal systems and space groups, which was clearly distinguished from the crystal structure of complex 3 and native β-cyclodextrin. These results indicated that the hydrogen bonding interconnection was a crucial and basic factor to govern the unique aggregation structures of supramolecular assemblies.