Host-Guest Chemistry and Reactivity
Encapsulation of Reactive Species
Ordinarily-pyrophoric white phosphorus (P₄) could be isolated as an air-stable complex through encapsulation by a water soluble tetrahedral Fe₄L₆ cage, providing striking example of the ability of metal-organic capsules to modulate guest reactivity. The same cage is also capable of selectively binding and sequestering the potent greenhouse gas SF₆ from a mixture of gases, preventing the climatic impact of releasing it into the atmosphere, and has been used as a whole molecule ‘supramolecular protecting group’.
Selective guest binding and sensing
Some of our cages can selectively bind guests thanks to a good match between cavity and guest shapes as well as complementary interactions. A variety of guest types can be bound such as natural products[1,2] or anions,[3,4] among others. Cages can be designed to serve as sensor for the desired guests by incorporating, for example, fluorescent moieties.
Complex host-guest assemblies
In addition to binding a single guest we have used metal-organic capsules to bind multiple guests or guests that can also act as hosts. A large tetrahedral capsule constructed from metalloporphyrin-based subcomponents was able to form host-guest complexes containing up to four fullerenes allowing the electronic properties of these unique fullerene clusters to be tuned through encapsulation. Another tetrahedron was able to encapsulate a covalent cage, cryptophane-111 (CRY) which was in turn capable of accommodating a cesium cation or xenon atom, with altered kinetics and thermodynamics compared to the CRY host alone. Enantiopure CRY could be bound with high enantioselectivity and stereochemical information was transfered from the inner covalent cage to the outer self-assembled capsule, leading to the formation of enantiopure Russian Doll complexes.
New nanoscopic environments
Self-assembled cages can be constructed with a variety of panels that will create a new environment – a nanospace – for encapsulated guests. This new nanoscale environment can be used to probe the response of guests in conditions normally inaccessible on a macroscopic scale.[1,2]