Effect of the Dipole-Dipole Interaction on the Self-Assembly of Cyclodextrin Inclusion Complexes

Abstract

We performed scanning tunneling microscopy (STM) observations on self-assembled α-cyclodextrin (CyD) inclusion complexes on HOPG for the guest compounds of (1) H₂O, (2) MeOH (Methanol) and (3) p-NP (p-nitrophenol). The observed structures of α-CyD-H₂O and α-MeOH complexes were channel-like with twofold symmetry, however, α-CyD-p-NP showed a structure different from that of the others, namely, a threefold symmetric arrangement. On the other hand, the dipole moments calculated for α-CyD-H₂O and α-MeOH complexes were similar and directed from the secondary to the primary hydroxyl groups of the α-CyD. However, the dipole moment on the α-CyD-p-NP complex was oblique to the axis for the other two complexes. Taking into account this difference in the dipole moment and the hydrogen bonding between the CyDs, the structural differences observed by STM could be explained comprehensively. The obtained results indicate the existence of a high potential for the structural control of the self-assembled α-CyD complexes by changing the guest compounds.