A self-assembled cylindrical capsule:: New supramolecular phenomena through encapsulation

The synthesis and spectroscopic characterization of self-assembled cylindrical capsule 1a.1a of nanometer dimensions is described. Encapsulation studies of large organic guest molecules were performed by using H-1 NMR sprectroscopy in [D-12]mesitylene solution. In addition to the computational (MacroModel 5.5, Amber* force field) analysis of the capsule's shape and geometry, an experimental approach towards estimation of the internal cavity dimensions is described. This involves using series of homologous molecular "rulers" (e.g. aromatic amides 5a-i). The available space inside the capsule la la can be estimated as 5.7 x 14.7 Angstrom (error +/- 0.2 Angstrom) with this technique. Dibenzoyl peroxide is readily encapsulated in [D-12]mesitylene and was shown to be stable to decomposition for at least three days at 70 degrees C inside the capsule. Moreover, 1a.1a prevents the encapsulated peroxide from oxidizing Ph3P or diphenyl carbazide present in solution. The normal chemical reactivity of the peroxide is restored by release from the capsule by DMF, a solvent that competes for the hydrogen bonds that hold the capsule together. The protection and release of encapsulated species augurs well for the application of capsules in catalysis and delivery.