Formation, characterization, and thermal degradation behavior of a novel tricomponent aggregate of beta-cyclodextrin, ferrocene, and polypropylene glycol

A tricomponent aggregate PPG-Fc-beta-CD formed by polypropylene glycol (PPG), ferrocene (Fc), and beta-cyclodextrin (beta-CD) was obtained and characterized by a series of physical methods, such as (1)H nuclear magnetic resonance, flame atomic absorption spectrometry, high performance liquid chromatography, UV-vis absorption spectroscopy, thermogravimetry, and gas chromatography coupled to time-of-flight mass spectrometry. First, the tricomponent aggregate exhibited a component ratio of 1:28:32 (PPG/Fc/beta-CD) in the solid state, and showed a completely different order in thermal stability when compared with beta-CD: under a nitrogen atmosphere, beta-CD > PPG-Fc-beta-CD, and in a vacuum, PPG-Fc-beta-CD > beta-CD. Second, the appearance of two peculiar points p and q at the end of TG curve of the aggregate gave a strong impression that the degradation rate further increased after the sharp decomposition of the aggregate reached point p and the amount present in the residual fraction at point q about 780.0 K was lower than 1%, both of which were rather different from those reported previously. This finding implied that the molecular assembly resulting from the binding interaction among Fc, PPG, and beta-CD induced more efficiently the degradation of each of them. Third, an interesting phenomenon was found that the order of thermal release of the three assembled components in PPG-Fc-beta-CD was Fc > beta-CD > PPG. Results of this study provide some insight into an initial attempt to construct a supramolecule among a polymer, a coordination compound, and an organic compound.