Supramolecular Catalysis And Self-Assembly Based On Cucurbiturils

Supramolecular catalysis,which was originally inspired by natural enzymatic catalysis,refers to the modulation on the rate and the direction of chemical reactions based on the noncovalent interactions,such as hydrogen bonding,electrostatic interaction and host-guest interaction.In comparison to natural enzymes,supramolecular catalysts are always with simpler structure,easier to modify and more robust under various conditions.Meanwhile,supramolecular catalyst is able to be designed on the chemical reactions which do not have counterparts in biological systems.We have developed a supramolecular catalysis system based on cucurbit[8]uril and Brooker’s merocyanine.Because of the product inhibition effect,cucurbituril usually has to be added in a stoichiometrical extent.However,in this supramolecular catalysis system,1% of cucurbit[8]uril was sufficient to catalyse the photodimerization of Brooker’s merocyane to the end within a short period(~ 10 min).We proved that in this system,cucurbit[8]uril acted as a catalyst but not a reactant,and we also investigated the reasons for the high catalytic activity of cucurbit[8]uril.Supramolecular polymers refer to the polymeric arrays of monomeric units that are linked by noncovalent interactions with reversibility and directionality.As most of the supramolecular polymers are under thermodynamic equilibrium once prepared,in which the monomers are frequently converging and splitting all the time,the molecular weight of supramolecular polymers is always dependent on the concentration of monomers.Therefore,when monomer concentration is constant,the molecular weight of supramolecular polymers is hard to be adjusted continuously.We have employed the supramolecular catalysis system of cucurbituril/Brooker’s merocyanine for the modulation on the molecular weight of supramolecular polymers.We synthesized a ditopic monomer with Brooker’s merocyanine moieties and mixed it with cucurbit[8]uril.By tuning UV irradiation time,we obtained the supramolecular polymers with different molecular weight under the same origianal concentration of monomer.By varying the wavelength of UV light source and adding competitive guest molecules,respectively,the controllable disassociation of the supramolecular polymers is realized.