Hexasulfonated Calixarene Derivatives: A New Class of Catalysts, Surfactants, and Host Molecules

Article abstract of DOI:10.1021/ja00269a045

Water-soluble hexasulfonated calix<6>arenes with various substituens (1-R) have been sythesized for the first time and applied as host molecules in an aqueous system.Dynamic ¹H NMR studies established that calix<6>arene-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)calix<6>arene (1-C) adopts a similar conformation in D2O 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. 6E-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-anilinonaphtalene, 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 calix<6>arene derivatives efficiently accelerate acid-catalysed hydration of 1-benzyl-1,4-dihydronicotinamide and the reaction proceeds according to the Michaelis-Menten kinetics.In particular, the rate constans for 1-H and 1-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 calix<6>arenes 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.