Two Squares in a Barrel: An Axially Disubstituted Conformationally Rigid Aliphatic Binding Motif for Cucurbit[6]uril

Novel binding motifs suitable for the construction of multitopic guest-based molecular devices (e.g., switches, sensors, data storage, and catalysts) are needed in supramolecular chemistry. No rigid, aliphatic binding motif that allows for axial disubstitution has been described for cucurbit[6]uril (CB6) so far. We prepared three model guests combining spiro[3.3]heptane and bicyclo[1.1.1]pentane centerpieces with imidazolium and ammonium termini. We described their binding properties toward CB6/7 and alpha-/beta-CD using NMR, titration calorimetry, mass spectrometry, and single-crystal X-ray diffraction. We found that a bisimidazolio spiro[3.3]heptane guest forms inclusion complexes with CB6, CB7, and beta-CD with respective association constants of 4.0 x 10(4), 1.2 x 10(12), and 1.4 x 10(2). Due to less hindering terminal groups, the diammonio analogue forms more stable complexes with CB6 (K = 1.4 x 10(6)) and CB7 (K = 3.8 x 10(12)). The bisimidazolio bicyclo[1.1.1]pentane guest forms a highly stable complex only with CB7 with a K value of 1.1 x 10(11). The high selectivity of the new binding motifs implies promising potential in the construction of multitopic supramolecular components.

Automated summary

Novel binding motifs suitable for the construction of multitopic molecular devices are needed in supramolecular chemistry. In this study, we prepared three model guests and investigated their binding properties towards cucurbit[6]uril (CB6)/7 and alpha-/beta-CD. The new binding motifs showed high selectivity and stability, indicating promising potential in the construction of multitopic supramolecular components.