Inclusion complexation of γ-cyclodextrin and coumarin dye inside alumina nanopores over a temperature range of 303-233 K

In the present study, we aimed to demonstrate that complexation reactions inside an inorganic water-filled nanopore can be enhanced at below the homogeneous nucleation temperature of bulk water (273 K). Using fluorescence experiments, we examined the inclusion complexation of propylamide coumarin 343 (PAC343) with γ-cyclodextrin (γ-CD) inside cylindrical alumina nanopores over a temperature range of 303-233 K. A PAC343-immobilized porous anodic alumina membrane (PAC343-PAA) with a pore diameter of ca. 70 nm was fabricated, and its fluorescence spectra were measured after introduction of aqueous γ-CD solution into the alumina nanopores. Our results confirmed that the inclusion complexation reaction was gradually enhanced with decreasing temperature, particularly at temperatures between 273 and 233 K. The inclusion complexation reaction was confirmed to be exothermic from van't Hoff analysis of adsorption constants of γ-CD obtained at temperatures between 288 and 283 K. These results confirm low-temperature (T < 273 K) conditions to be useful for enhancing exothermic complexation reactions that occur inside alumina nanopores filled with water.