A self-assembled cylindrical capsule: New supramolecular phenomena throughencapsulation

The synthesis and spectroscopic characterization of self-assembled cylindri cal capsule 1a.1a of nanometer dimensions is described. Encapsulation studi es of large organic guest molecules were performed by using H-1 NMR sprectr oscopy in [D-12]mesitylene solution. In addition to the computational (Macr oModel 5.5, Amber* force field) analysis of the capsule's shape and geometr y, an experimental approach towards estimation of the internal cavity dimen sions is described. This involves using series of homologous molecular "rul ers" (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 t his technique. Dibenzoyl peroxide is readily encapsulated in [D-12]mesityle ne and was shown to be stable to decomposition for at least three days at 7 0 degrees C inside the capsule. Moreover, 1a.1a prevents the encapsulated p eroxide 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 th e capsule together. The protection and release of encapsulated species augu rs well for the application of capsules in catalysis and delivery.