Double Capping

As cyclodextrins possess more than two hydroxyls on their primary rim, a second capping reagent can be attached. This would lead to tetrafunctionalized cyclodextrins. This second reaction is more difficult, as the primary rim becomes more crowded after the introduction of the first cap, but as a consequence it is also more selective. Some of the few tetrafunctionalizations of -cyclodextrin have been achieved through installation of two capping groups on its primary rim. 

Modification of Capped Cyciodextrins 9.3.3.1 Addition of Another Functionaiity 

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Perera and Amar (1989) found more detailed support for the structural control of caging in classical dynamics calculations on a model of Br2 in large clusters of Ar and C02. The dissociation channel was found to become closed, as a function of cluster size, between 11 and 12 C02 molecules in the BrJ(C02)M clusters, correlating with the appearance of double-capped minimum energy structures. This correlation was found in the Br2 Ar clusters as well. Collisions between a vibrating diatomic molecule in a cluster and the solvent particles may cause V-T energy transfer and rapid evaporation of the cluster. 

Scheme 9.13 Double capping gives access to original patterns of functionalization on the prima7 rim of P-cyclodextrin.

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