An inclusion complex (1) has been prepared by β-cyclodextrin with α-aminopyridine. The result of X-ray crystallographic analyses showed that the α-aminopyridine molecules in the β-cyclodextrin cavities possess two opposite orientations, i.e. the amine group of α-aminopyridine pointing to the primary side (1a, occupancy: 41.2%) or the secondary side (1b, occupancy: 58.8%) of β-cyclodextrin, forming two scalelike supramolecular aggregations. The studies of 2D NMR and circular dichroism spectra indicated that the α-aminopyridine molecule is deeply embedded in the β-cyclodextrin cavity to form host-guest inclusion complex, showing a circular dichroism spectrum induced by the chiral cavity of cyclodextrin. The results obtained are helpful for understanding the molecular recognition and aggregation mechanism between the host and guest.
The self-assembly behavior of mono(6-phenolic-6-deoxy)-β-cyclodextrin bothin solution and the solid state is comparatively studied by X-ray crystallography and ~1H NMRspectroscopy. The results obtained show that the phenolic groups in the crystal 1 can successivelypenetrate into the adjacent β-cyclodextrin cavities from the secondary side to form head-to-taillinear polymeric su-pramolecule with a 2-fold screw axis. The self-assembly behavior also can bedetermined in D_2O solution, giving a self-association constant of 240 mol^(-1)·L. Using thepresent and previous structures reported for the relevant β-cyclodextrin derivatives, i.e.,mono(6-anilino-6-deoxy)-β-cyclodextrin, mono(6-phenylselenyl-6-deoxy)-β-cyclodextrin, andmono(6-phenylthio-6-deoxy)-β-cyclodextrin, we further reveal the factors governing the formationsof supramolecular assemblies.
