Sorption properties of the cucurbit[5–8]uril family towards water

Abstract

The water vapor sorption and desorption kinetics of the cucurbit[n]uril (CB[n]) homologues (n = 5–8) were investigated. Kinetic analysis revealed that the water uptake capacity varies as a function of cavity size with CB[5], CB[6], CB[7] and CB[8] exhibiting sorption of 8, 12, 18 and 17 mol H₂O per mol of host, respectively. The corresponding sorption equilibria were attained over 270, 320, 210 and 300 min, while complete desorption required 270, 390, 450 and 400 min, respectively. Experimentally derived rate constants for sorption (k_sorp) and desorption (k_des) were determined as follows: CB[5] k_sorp = 0.0172 min^− 1, k_des = 0.0101 min^− 1; CB[6] k_sorp = 0.013 min^− 1, k_des = 0.0047 min^− 1; CB[7] k_sorp = 0.0195 min^− 1, k_des = 0.039 min^− 1; CB[8] k_sorp = 0.0129 min^− 1, k_des = 0.0063 min^− 1. Notably, the highest sorption rate constants were observed for CB [5] and CB [7], which also demonstrate comparatively greater aqueous solubility, suggesting a possible correlation between hydration affinity and solubility behavior.