Investigation on γ -cyclodextrin nanotube induced by N,N′N,N′-diphenylbenzidine molecule

Dynamic light scattering (DLS) measurement provides an effective way to investigate the formation of nanotube of γ-cyclodextrin (γ  -CD) induced by N,N′N,N′-diphenylbenzidine (DPB) in water. With the combination of steady-state fluorescence and fluorescence anisotropy experiments, it was found that for α- and β-CD, only 1:2 (guest:host) inclusion complexes were formed and for γ-CD, cyclodextrin nanotube was formed involving 16 γ-CD units at maximum. The pH effect studies with both DLS and fluorescence anisotropy measurements indicated that the hydrogen bonding between neighboring CDs was necessary to the formation of cyclodextrin nanotube. In the temperature experiment, we found that the nanotube of DPB-γ-CD could exist stably at relatively high temperatures and the transition point for structural collapse was estimated to be around 54 °C. The aggregation states of both γ-CD itself and DPB-γ-CD nanotube were observed with TEM.