Water-soluble hexasulfonated calixarenes with various substituents (1-R) have been synthesized for the first time and applied as host molecules in an aqueous system. Dynamic 1H NMR studies established that calixarene-p-hexasulfonate (1-H) adopts a “winged” or “hinged” conformation in D2O-Me2SO-d6 (2:1 v/v) owing to hydrogen bonding among the OH groups, while 5,11,17,23,29,35-hexasulfonato-37,38,39,40,41,42-hexakis(hexyloxy)calixarene (1-C6) adopts a similar conformation in D20 owing to hydrophobic bonding among the hexyl groups. The aggregation behavior in water was examined about 1-C6 and 1-C12. Physical (light-scattering, surface tension, and conductance) and spectral (fluorescence and absorption spectroscopies) studies established that 1-C6 has a cmc at ca. 6 X 10-4 M, as does sodium dodecyl sulfate (SDS), while 1-C12 has no detectable cmc and rather acts as a “unimolecular” micelle. In fact, 1-C6 associated with small molecules (pyrene, 2-anilinonaphthalene, and Orange OT) according to the micelle-like biphasic concentration dependence, while 1-C12 formed host-guest-type 1:1 complexes with these molecules. It was found that these calixarene derivatives efficiently accelerate acid-catalyzed hydration of 1-benzyl-1,4-dihydronicotinamide and the reaction proceeds according to the Michaelis-Menten kinetics. In particular, the rate constants for 1-H and l-CH2COOH, which both have acidic protons to catalyze the reaction and anionic sulfonates to stabilize the cationic intermediate at the two edges of the cavity, were greater by 426-1220-fold than those for noncyclic analogues. These findings indicate that hexasulfonated calixarenes serve as a new class of catalysts, surfactants, and host molecules. This is the first example for the host-guest-type behavior of calixarenes observed in an aqueous system.
All Science Journal Classification (ASJC) codes
- Colloid and Surface Chemistry