Cucurbituril With The Catalytic Oxidation Of Ascorbic Acid

The kinetics of oxidation of L-Ascorbic acid catalyzed by transition metal ions(Cu²⁺,Ni²⁺,Co²⁺ and Zn²⁺) and their complexes with cucurbitt[n,n=5-8]urils,β-cyclodextrin has been studied by UV-vis absorption spectroscopy. The catalysis activity of metal ions has been improved when ions formed cooradinated complexes with cucurbit[n,n=5-8]urils. The catalysis activity depends on species of metal ions and is independent of the cavity size of cucurbiturils. The electrode potential have been employed to thermodynamically study the oxidative ability of metal ions and their complexes with cucurbiturils, and it shows that oxidation activity of metal ions would be improved after coordinating with cucurbiturils. In addition, we have successfully synthesized and characterized the complexes of Cu²⁺,Ni²⁺ and Zn²⁺ with (2-aminomethyl)pyridine ligand. Single crystal X-ray diffraction and infrared spectrum have been used to analyses the structures of the complexes. The interaction between the three metal complexes and cucurbit[n, n=6-8]urils has been investigated by fluorescence spectroscopy method. And the interaction models of 1:1 between guests and cucurbit[n, n=6-8]urils is obtained. UV-vis absorption spectroscopy is employed to investigate oxidation of L-Ascorbic acid catalyzed by metal complexes in the present of cucurbiturils. The catalysis ability of metal coordinations is weaker than the free metal ions'. Moreover, the zinc complex with (2-aminomethyl) pyridine can restrain the self-oxidation of L-Ascorbic acid in air. It has been approved that the rate of oxidation of L-Ascorbic acid increased in the present of cucurbiturils. Compared with the first-sphere complex mat formed by metal ion with cucurbiturils, the formation of second-sphere complex of metal complexes with cucurbiturils resulted in weakly interaction between cucurbiturils and ion center and their worse catalysis activity.