Slippage and Constrictive Binding

Abstract

Kinetically stable superarchitectures can be constructed efficiently by relying upon the assistance that mechanical constraints can offer to noncovalent bonding interactions. Thus, the free energies of binding and activation associated with complexation/dissociation processes are determined by the combined strengths of the noncovalent bonds formed by, and by the size complementarity between, the constituents of a complex, as well as by the differential solvation between the complexed and dissociated states. Using this information, kinetically stable complexes can be constructed through the careful design of stereoelectronicallymatching components and the judicious selection of the experimental conditions under which they are brought together. Rotaxanelike complexes, prepared via the slippage of appropriately sized macrocycles over the stoppers of chemical dumbbells, and hemicarceplexes, created via the ingression of a guest into a hemicarcerand's cavity, are examples of kinetically stable species that can be synthesized noncovalently through the combined action of noncovalent bonding and mechanical coercion. The synthetic protocol brought to light by the syntheses of these complexes holds considerable promise for the future construction of nanosized devices, with specific shapes, sizes and functions, the fabrication of which is impracticable by classical synthetic routes.