Self-assembled hemicapsules with inherent functionalities: Modeling of a supramolecular electrostatic self-assembly

An approach to functional self-assembled hemicapsules is described consisting of the use of multivalent (valency g 4) and divalent components, the functional groups of which have a relatively weak binding affinity. Electrostatic self-assembly of tetrakis(pyridiniummethyl) cavitand hemispheres (H) and doubly charged anions (A) in polar media gives rise to an equilibrium mixture that consists, as detected with ESI-MS, of hemicapsule H(2)A(3), capsule H(2)A(4), and other ion-pair associates. Fitting H-1 NMR data with a model that includes (hemi) capsules and ion-pair associates gave an effective molarity (EM) for the intramolecular assembly of the host (H) with sulfate (A) of 0.19 +/- 0.02 M and binding constants of the functional [2 + 3] hemicapsules H(2)A(3) and the [2 + 4] capsules H(2)A(4) in methanol of 3.25 x 10(12) M-4 and 3.45 x 10(15) M-5, respectively. A substantial amount of the functional [2 + 3] hemicapsules H(2)A(3) with respect to [2 + 4] capsules H(2)A(4) is present in solution, with ratios of H(2)A(3) to H(2)A(4) of 5.67-0.43 in the studied concentration range (0.1-25 mM of [H] tot). The [2 + 3] hemicapsules H(2)A(3) built with sulfate linkers incorporate guests between the closely positioned pyridinium planes.