Self assembling cyclodextrin systems-from vesicles to genocomplexes

The concept of cooperativity between cyclodextrin host molecules is essential for the attainment of better binding constants for such purposes as the targeting of complexed drugs to their biological sites of action. Recent advances in supramolecular, non-bonded approaches to attaining cooperativity are reviewed here. Amphiphilic cyclodextrins can form monolayers and nanoparticles, thermotropic liquid crystals or micelles. More recent examples form bilayer vesicles. Amphiphilic cyclodextrins with alkylthio chains at the primaryhydroxyl side and oligo-(ethylene glycol) units at the secondary-hydroxyl side form colloidal assemblies, and where these are vesicular they encapsulate both polar and hydrophobic guest molecules as complexes which are stable towards dilution. When modified with surface glycosyl groups for targeting, they show multivalent effects in their binding to lectin. Polyionic cyclodextrins can exploit multiple interactions to assemble in water. Use of ionic CDs in polyelectrolyte multilayers has been shown to modulate the bioactivity of a compound complexed within the layers. Amphiphilic cyclodextrins have also been proposed as molecular templates for the development of a new series of gene delivery vectors. Comparison of polycationic examples with analogous polycationic amphiphilic CDs, has shown that amphiphilicity is important for vector activity.