Hemicarcerands self-assembly

Keywords Constrictive Binding m Crown Ethers m Hemicarcerands a Host-Guest Chemistry a Noncovalent Interactions aRotaxanes a Self-Assembly a Slippage a Supramolecular Chemistry... 

The relatively low thermodynamic stability of complexes of hemicarcerands or other container-type hosts is a direct consequence of structural aspects of the walls that make up the inner surface of such compounds. These walls are lined by aromatic subunits while free electron pairs of heteroatoms such as those of the ether oxygen atoms are preferentially oriented to the outside. Complexes are therefore enthalpically stabilized only by weak dispersive interactions. In the case of positively charged guests cation-re interactions can contribute to binding enthalpy as in a self-assembled calixarene-derived capsule [9], but directed interactions such as hydrogen-bonding interactions are usually absent. 

Carcerands and Hemicarcerands, p. 189 Cryptophanes, p. 340 Glycoluril-Based Hosts, p. 597 Hydrogen Bonding, p. 658 Micelles and Vesicles, p. 861 Molecular Squares, Boxes, and Cubes, p. 909 Platonic and Archimedean Solids, p. 1100 Self-Assembly Definition and Kinetic and Thermodynamic Considerations, p. 1248 Self-Assembly Terminology, p. 1263 Soft and Smart Materials, p. 1302... 

Egg-shaped or spherical capsules can be formed by the assembly of two halves or hemispheres. Like then-covalent carcerand and hemicarcerand counterparts, self-assembled capsules are of interest for drug delivery and as containers for stabilizing reactive intermediates and for inducing selectivity in reactions. Capsules have been... 

The efficiency of these hemicarcerand and polycavitand nanocapsule syntheses approaches those of self-assembly processes using hydrogen bonding or metal-ligand coordination and results from selection of the least strained capsule through the thermodynamic control and reversibility of the system. 

The early 2000s were an intense time for metal coordination via the two-position and the assembly of cavitands into dimeric capsules. Work in the Kobayashi group focused on using palladium coordination to assemble capsules from 17,18, and 19 (Fig. 9.8) [67]. Around the same time the Reinhoudt group examined the assembly of 20 on gold surfaces [68]. Kobayashi s further work examining assemblies with two different cavitands showed that self-sorting into either homo- or hetero-cavitand hemicarcerands was controlled by a balance of factors such as... 

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