The kinetic parameters of deswelling on a freeze-dry-treated poly(N-isopropylacrylamide) gel were investigated using glucose and maltose as hydrophilic probes. The activation entropy change at 313K (ΔS_(313)) shifted from negative (-190 J K~(-1)mol~(-1)) in water to positive (+410 J K~(-1)mol~(-1)) in 0.2 M glucose. This is explained by the structural similarity between β-D-glucopyranose and water clusters. β-D-Glucopyranose retains the normal C1 conformation (chair form). On the other hand, a water cluster processes a tridymite-structure. Consequently, the equatorial OH of glucose can easily form hydrogen bonds with the surrounding water in the gel. The apparent activation energy (E_a) and ΔS_(313) are higher in 0.2 M glucose than in water, which may reflect the presence of larger clusters of the iceberg around isopropyl groups in the presence of hydrophilic glucose possessing many hydroxyl groups in equatorial positions.
展开▼
