Duplex of capped-cyclodextrins, synthesis and cross-linking behaviour with a biopolymer

Abstract

Doubly connected cyclodextrin (CD) dimers, called duplexes, have the ability to cross-link hydrosoluble biopolymers grafted with a hydrophobic moiety, inducing a viscosity increase of the solution through formation of stable supramolecular assemblies. CD duplexes behave differently according to the nature of their inter-CD links. CD duplex with hydrophobic links has a better affinity for adamantane, but suffers from a lack of availability of its cavities, both phenomena being attributed to the hydrophobicity of its spacer arms. In the case of the CD duplex with hydrophilic links, all its cavities are available, but its affinity for adamantane is lower. We report here on the synthesis of a CD duplex displaying an original topology consisting of two capped and doubly connected concave rings. It possesses a hydrophobic arm on the CD primary face which induces an increased binding affinity for adamantane, and hydrophilic inter-CD links to keep all its cavities accessible. The cap was selected according to the binding efficiency of the monomeric capped-CD with adamantane determined by isothermal calorimetry (ITC) experiments. The synthesis of this challenging and unprecedented edifice consisting of two capped CDs doubly linked to each other was made possible thanks to our cyclodextrin debenzylation strategy, as well as the extensive use of metathesis reaction. ITC experiments with the duplex confirmed its better affinity for adamantane compared to the uncapped duplex. However, viscosity measurements revealed that capped and uncapped CD duplexes had similar cross-linking behaviour.