Supramolecular capsules

Kim. H.-J., Moon, D., Lah, M.S. and Hong, f.-I. (2002) An enantiomerically pure propeller-shaped supramolecular capsule based on the stereospecific self-assembly of two chiral tris(oxazoline) ligands around three Ag(I) ions. Angeiv. Chem., Int. Ed., 41, 3174-3177. 

Hydrogen-bonded supramolecular capsule I compared with coordination capsule II. The external aliphatic groups are omitted for clarity. Note that a pair of intermolecular O—H O hydrogen bonds is replaced by four square-planar Cu-O coordination bonds in the metal-ion insertion process that generates the isostructural inorganic analog. From R. M. McKinley, G V. C. Cave and J. L. Atwood, Proc. Nat. Acad. Sci. 102, 5944-8 (2005). 

Fig. 27 A A chiral object like a hand in an achiral environment leaves a chiral space available. B Spherical supramolecular capsules are much less suitable compared to C cylindrical ones for enantiorecognition because of the greater number of possible reciprocal orientations of two co-guests encapsulated...

Fig. 2.14 Supramolecular capsule formation top) the tennis ball [28] and (bottom) hemisphere approach [29]...

Cavitands and Calix[n]arenes Building Blocks for Supramolecular Capsules. 101... 

Moreover, the inner cavity of supramolecular capsules provides a discrete, well-defined environment ideally suited to investigate effects of compartmentalization and processes in confined spaces [8]. To realize technical applications as detection and stabilization of encapsulated molecules or their use as nano-sized reaction vessels, precise control of important factors such as size, stability, porosity of the walls, and functionalization of the inner surface have to be achieved [9-18]. Several capsules have been synthesized and a proof of principle for several applications has been provided, but in most cases their use is restricted to small guest molecules. The development of spacious architectures which are able to encapsulate several bulky molecules and are amenable for decoration of the inner surface with functional groups will constitute an important step on the way to functional systems. 

The synthesis of hollow architectures based on cavitands started in 1985, when Cram et al. reported on the inclusion of solvent molecules in a carcerand obtained by covalent linkage of two cavitands [30]. Since then, molecular and supramolecular capsules have been prepared from cavitands and calix[n]arenes due to two important properties the bowl-shaped form and the various functionalizations which can be introduced at the upper rim of the cavitands or the wider rim of the calix[n]arenes (Fig. 1). 

The kind of attachment of the metal coordinating groups to the cavitand is an important structure-defining parameter. Hong et al. studied the self-assembly of a cavitand 15 functionalized with pyridyl groups via flexible ether linkages (Fig. 5) [48, 49]. Due to the conformational freedom of the connection, intramolecular coordination of the metal (Pt2+ and Pd2+) centers is observed in competition with intermolecular complexation leading to the supramolecular capsules 16a-b. While the capsules 16a b and the half-capsules 17a-b are in dynamic equilibrium in nitromethane, the dimeric capsule is formed exclusively in chloroform/methanol mixtures. 

Dalgamo SJ, Power NP, Atwood JL (2008) Metallo-supramolecular capsules. Coord Chem Rev 252 825... 

Schroder T (2010) Synthesis and single-molecule force spectroscopy of supramolecular capsules. PhD Thesis, Bielefeld University, Bielefeld... 

Schroder T, Sahu SN, Anselmetti D, Mattay J (2011) Supramolecular capsules derived from resorcin[4]arenes by H-bonding and metal coordination. Synthesis, characterization and single-molecule force spectroscopy. Isr J Chem 51 725... 

Park SJ, Shin DM, Sakamoto S, Yamaguchi K, Chung YK, Lah MS, Hong JI (2005) Dynamic equilibrium between a supramolecular capsule and bowl generated by inter- and intramolecular metal clipping. Chem Eur J 11 235... 

Very Large Supramolecular Capsules Based on Hydrogen Bonding... 

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