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

Abstract

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 ¹H 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 10³ and 10⁶ 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.