Construction Of Cucurbituril Molecular Reactors And Inhibition On H-d Exchange Of β-Carbonyl Esters

The cucurbiturils (CB[n], n=5-10) are macrocyclic supramolecules, comprised of n glycoluril units bridged by2n pairs of methylene groups. The cucurbiturils contain an interior hydrophobic cavity100-500A3with polar carbonyl groups surrounding the two identical portals. It can form host-guest complexes with guest molecules through ion-dipole interactions, hydrophobic effect or hydrogen b. onds, thus change the chemical properties of the guest. It is an ideal molecular reactor for its interior hydrophobic cavity is a favourable place for chemical reaction. CB[n] as catalyst were investigated in a variety of reactions, such as hydrolysis reaction, solvolytic reaction, desilylation reaction, oxidation reaction and photoreaction.A vast variety of neutral organic small molecules with different structures have been encapsulated into the cavity of cucurbit[6]uril macrocyclic molecule, through ionic liquid EmimBr replacement method.42neutral molecules have been screened, and totally26host-guest complexes have been prepared such as acid, ester, ketone, alkane, aromatic compounds and heterocyclic compounds et al. The cucurbit[6]uril complexes thereby formed have been characterized by NMR spectroscopy, elemental analysis and thermogravimetric analysis. Further the difference on encapsulation of various molecular structures has been discussed. The research provided a general approach to construct cucurbit[6]uril molecular reactors encapsulating kinds of neutral small molecules.During preparation of cucurbit[6]uril complexes, H-D exchange of β-carbonyl ester has been observed. cucurbit[7]uril was chosen to investigate the effect of cucurbiturils on H-D exchange, due to its higher solubility in H2O. Firstly1H NMR titration experiments were performed to investigate the binding constants of β-carbonyl esters with cucurbit[7]uril:644M-1for cucurbit[7]uril? ethyl acetoacetate,881M-1for cucurbit[7]uril? methyl acetoacetate and145M"1for cucurbit[7]uril? dimethyl malonate. Fast exchange on the NMR time scale was ensured for only one set of guest peaks being observed when cucurbit[7]uril less than1equivalent. The H/D exchange reactions in pD=3.9were monitored by1H NMR spectroscopy and the rate constants have been acquired at the condition of with and without cucurbit[7]uril. The influence were found to vary with different structures ofβ-carbonyl esters in the order:methyl acetoacetate> ethyl acetoacetate> dimethyl malonate, which is in reasonable agreement with that of binding constants.