Sulfonated Calix[6]arene Host-Guest Complexes Induce Surfactant Self-Assembly

The results obtained in a study of a mixed system based on 5,11,17,23,29,35-hexasulfonato-37,38,39,40,41,42-hexamethoxycalix[6]arene (1) and the cationic surfactant dodecyltrimethylammonium bromide (2), are presented. The results show that the host-guest complex formed by 1 and 2 self-aggregates at lower concentrations than the pure surfactant alone. This result can be explained in terms of the surfactant properties of the host-guest complex and its self-aggregation to form micelles. Calixarenes are flexible hosts that can adopt several conformations depending on the substituents present on the lower and upper rims. Molecular modeling calculations also indicated that 1 is highly flexible, as the authors could not locate a clearly defined energy minimum. NMR titration experiments were performed to gain more of an insight into the behavior of the 1:2 mixed system. The proximity of calixarene molecules causes the chemical shifts to move upfield as a result of the aromatic ring current effects.