The underestimated role of counter ions in electrostatic self-assembly: [1+1] cavitand-calix[4]arene capsules based on azinium-sulfonate interactions

The apparent K-a values of the formation of [1+1] cavitand-calix[4]arene capsules, based on azinium-sulfonate electrostatic interactions, obtained by direct titration experiments are concentration dependent due to the influence of the interaction of the charged capsule components with their initial counterions. H-1 NMR and UV dilution experiments, in which this ion-pairing is excluded, gave K.-values larger than 2 center dot 10(6) M-1 in methanol and methanol/water (1:1) for the capsule formation. The capsule encapsulates small guests like methanol, ethanol, etc., as proven by ESI-MS. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)