Thermodynamic analysis of inclusion complexation between α-cyclodextrin-based molecular tube and poly(ethylene oxide)-block-poly(tetrahydrofuran)-block-poly(ethylene oxide) triblock copolymer

Thermodynamic analysis of inclusion complexation between a-cyclodextrin-based molecular tube (MT) and poly(ethylene oxide)-block-poly(tetrahydrofuran)-block-poly(ethylene oxide) triblock copolymer (PEO-b-PTH-Fb-PEO) was carried out in terms of isothermal titration calorimetry. As for the titration of MT to PEO in aqueous solution, no strong exothermic peak was observed. On the contrary, strong exothermic peaks were observed for the titration of MT to PEO-b-PTHF-b-PEO in aqueous solution, which is attributable to inclusion complexation between MT and the triblock copolymer. Thermodynamic parameters were obtained for the process of inclusion complexation between MT and PEO-b-PTHF-b-PEO by changing the molecular weight of MT and the temperature. The stoichiometry of inclusion complexation changes in relation to the molecular weight of MT. Interestingly, it was found that MT with a large molecular weight behaves as the host molecule having multibinding sites. Thermodynamic parameters suggested that van der Waals interaction, hydrophobic interaction, and hydrogen bond play an important role to determine the magnitude of DeltaH. Some thermodynamic parameters clearly indicated that the dehydration of the triblock copolymer is a key factor in inclusion complexation between MT and PEO-b-PTHF-b-PEO. These results afford a deeper insight into the mechanism of the macromolecular recognition process.