Multiple ionic interactions for noncovalent synthesis of molecular capsules in polar solvents

The formation and characterization of molecular capsules resulting from the self-assembly between oppositely charged (thia)calix[4]arenes in polar solvents like MeOH and MeOH-H2O are reported. The multiple ionic interactions allow the self-assembly of the complementary (thia)calix[4] arenes 1 and 2a-d into 1 : 1 complexes as revealed by H-1 NMR and mass spectrometry (ESI-MS). Isothermal titration calorimetry (ITC) was used to determine the association constants, which, depending on the ionic groups involved in the complexes, vary between 10(3) and 10(6) M-1. An X-ray structure of the assembly 1.2d was also obtained. Unlike in solution, in the solid state 1.2d forms a 1 : 1 three-dimensional network in which 2d adopts a 1,2-alternate conformation.