Bis(polypseudorotaxane)s Formed by Multiple Metallo-Bridged β-Cyclodextrins and the Thermodynamic Origin of Their Molecular Aggregation

Abstract

Bis(polypseudorotaxane)s possessing the bridged bis(β-cyclodextrin)s with multicoordinated metal centers are prepared, in which β-cyclodextrin (β-CD) acts as the host structure, amino-terminated polypropylene glycol (PPG; MW = 2000) as the guest, and nickel(II) complexes as templating moieties. The assembly behavior is comprehensively studied by NMR spectroscopy, gel permeation chromatography (GPC), end group assay, static light scattering, thermogravimetric (TG), differential thermal analysis (DTA), and scanning tunneling microscopy (STM). The obtained results indicate that not only could the two PPG molecules be respectively threaded into metallo-bridged bis(β-CD)s forming the double-strand structure, but they also could play a stabilizing role in the molecular aggregation. The fluorescence titrations are performed in a mixture of acetonitrile/water to calculate the effective binding constants and thermodynamic parameters for the threading process of 2 onto PPG. The results reveal that the assembly proc...