Hexameric Capsules Studied by Magic Angle Spinning Solid‐State NMR Spectroscopy: Identifying Solvent Molecules in Pyrogallol[4]arene Capsules

Abstract

Powders of pyrogallol[4]arene hexamers were produced by evaporation from organic solvents and were studied, for the first time, by magic angle spinning solid-state NMR (MAS ssNMR). Evaporation selectively removed non-encapsulated solvent molecules leaving stable hexameric capsules encapsulating solvent molecules. After exposure of the powder to solvent vapors, (1)H/(13)C heteronuclear correlation MAS ssNMR experiments were used to assign the signals of the external and encapsulated solvent molecules. The formed capsules were stable for months and the process of solvent encapsulation was reversible. According to the ssNMR experiments, the encapsulated solvent molecules occupy different sites and those sites differ in their mobility. The presented approach paves the way for studying guest exchange, guest affinity, and gas storage in hexamers of this type in the solid state.

Requirements for Terpene Cyclizations inside the Supramolecular Resorcinarene Capsule: Bound Water and Its Protonation Determine the Catalytic Activity

“…Utilizing capsule I as an aromatic cavity with some similarities to natural cyclase enzymes, we were able to showcase some first examples: A four-step total synthesis of isolongifolene, the first total synthesis of δ-selinene, as well as a four-step synthesis of the complex tricyclic presilphiperfolan-1β-ol, which is difficult to access via other means. Interestingly, the closely related hexamer II , which is formed from six units of pyrogallolarene 2 (Figure b), has been found to be catalytically inactive in THT cyclizations . The reason for its inactivity, however, remained unknown.…”

Mechanically induced pyrogallol[4]arene hexamer assembly in the solid state extends the scope of molecular encapsulation

“…More recently, the Cohen group has studied pyrogallol[4]arene powders obtained by evaporation of CH 2 Cl 2 solutions using solid-state NMR. 25 They found evidence for solvent encapsulation within hexameric assemblies.…”

To catalyze or not to catalyze: elucidation of the subtle differences between the hexameric capsules of pyrogallolarene and resorcinarene

“…To learn more about the pivotal requirements for the catalytic activity of hexamer I , we became interested in the structurally closely related pyrogallolarene hexamer II . 5 It self-assembles from six units of pyrogallolarene 2 . Surprisingly, hexamer II displays a different encapsulation behavior compared to I in chloroform solution.…”