A Self-Assembled Cylindrical Capsule: New Supramolecular Phenomena through Encapsulation

Abstract

The synthesis and spectroscopic characterization of self-assembled cylindrical capsule 1a x 1a of nanometer dimensions is described. Encapsulation studies of large organic guest molecules were performed by using 1H NMR sprectroscopy in [D12]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 1a x 1a can be estimated as 5.7 x 14.7 A (error +/- 0.2 A) with this technique. Dibenzoyl peroxide is readily encapsulated in [D12]mesitylene and was shown to be stable to decomposition for at least three days at 70 degrees C inside the capsule. Moreover, 1a x 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.

Resorcinarenes with 2-benzimidazolone bridges: Self-aggregation, self-assembled dimeric capsules, and guest encapsulation

“…The synthesis and spectroscopic characterization of 2⅐2 have been recently described by Rebek and coworkers, showing remarkable encapsulation capabilities, like pairwise complexation of two different guests (11) or stabilization of reactive species, such as dibenzoyl peroxide (12). Both capsules 1⅐1 and 2⅐2 are of nanometer dimensions (about 1.0 ϫ 1.8 nm) (Fig.…”

Safe storage of radical initiators within a polyaromatic nanocapsule

“…Stabilization of highly reactive molecules in the confines of molecular capsules enabled the spectroscopic and even crystallographic observation of labile species such as cyclopolyenes 9,10 , benzyne 11 , peroxide 12 , phosphoniums 13 , oligosilanols 14 , iminiums 15 , hemiaminals 16 and white phosphorus 17 . The capsules function as protective, nanometre-sized containers and shield the guest molecules from external reagents, solvents, water and air.…”

Experimental and computational probes of the space in a self-assembled capsule

“…All chemicals were used without further purification unless otherwise specified. Cavitand 2 was prepared from corresponding resorcinarene as follows in an improvement on the published procedure (11). The acetylenes 4-ethynyl-4Ј-ethylbiphenyl (4b), 4,4Ј-diethynylbiphenyl (4c), and 4-ethynyl-4Ј-propylbiphenyl (4d) were prepared according to literature procedures (22).…”

“…Their gentle curvature and electronic properties attract cationic, convex molecules, but when the resorcinarene is deepened through synthesis, size selectivity can be seen and the molecules are regarded as cavitands (6)(7). Such cavitands can maintain their conformations through intramolecular hydrogen bonds along the upper rim (8-9), or, when intermolecular hydrogen bonding is possible, the formation of capsules 2.2 can occur (10)(11)(12). This capsule presents guests with an electronic environment dominated by the eight benzene rings at each end (13)(14)(15).…”