Effects of pressure on inclusion complexation of methylene blue with water‐soluble <i>p</i>‐sulfonatocalix[<i>n</i>]arenes

Abstract

Abstract The effects of pressure were examined for the inclusion complexation of water‐soluble p ‐sulfonated calix[ n ]arenes (Calix‐S n : n = 4, Calix‐S4; n = 6, Calix‐S6; n = 8, Calix‐S8) with methylene blue (MB). A differential pressure effect was found in the inclusion equilibria of Calix‐S n . As the external pressure increases, the inclusion equilibrium of MB with Calix‐S4 and Calix‐S6 shifts to the dissociation side. However, with Calix‐S8, the inclusion equilibrium shifts to the association side with increased pressure. From the pressure dependence of the inclusion equilibria of Calix‐S n , the reaction volumes, which are changes in volume accompanied by inclusion, were estimated as 32.1 cm 3 mol −1 for Calix‐S4, 30.1 cm 3 mol −1 for Calix‐S6 and −13.8 cm 3 mol −1 for Calix‐S8. In addition, the structures of the inclusion complexes of Calix‐S n with MB have been established by 1 H NMR measurements. Based on the results, the behavior of inclusion complexation with Calix‐S n is discussed. Copyright © 2004 John Wiley &amp; Sons, Ltd.