金屬紫質的多步驟選擇性電催化氧化反應研究及去活性反應的機制探討
| Autor: | Ellen Cheng, 鄭雅倫 |
|---|---|
| Rok vydání: | 2000 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 89 Manganese Tetrakis(N-methyl-4-pyridyl)porphine ( Mn(4-TMPyP) ) selectively catalyzes the oxidation of nerol and geraniol at the hydroxyl group to form aldehydes, neral and geranial, respectively. The products keep the original stereostructure of substrates. Manganese porphyrin plays a role of hydrogen atom abstractor in this catalysis. Citral, the mixture of neral and geranial, can be further oxidized by Mn(4-TMPyP) to give epoxides. The epoxidation selectively takes place at the 6,7 double bond of citral. It is the very especial thing that olefin catalyzed by Mn(4-TMPyP) in pH 7 buffer mixed solution undergoes a stepwise catalytic oxidation. First, alcohol was oxidized to aldehyde. Then, epoxidation takes place at the 6,7 double bond of the diolefin. However, the manganese porphyrin lost its catalytical capability as the pH of the solution increased to 10.0. Moreover, the manganese porphyrin showed no appreciable catalytic ability toward geranyl acetate. Semi-empirical calculation suggests that the spatial orientation may play an important role. Besides, kinetic study supports the reaction rate between geraniol and O=MnIV(4-TMPyP) is faster than other substrates. MnTSPP was alao used to be the catalyst in the same pH 10 buffer mixed solution at +1.0 V. There is no remarkable catalyical ability toward geraniol, citral, and geranyl acetate. Porphyrin ring cleavage is the major deactivation reaction in the process of heme catabolism. The process of porphyrin ring cleavage is thought to involve the formation of isoporphyrin. Endogenous isoporphyrin was formed in oxidation of amide linked zinc meso-tetraphenyl porphyrin (ZnPH). It exhibited three unusual reversible oxidative couples on cyclic voltammetry. The half-wave potentials are at +0.74, +1.07 and +1.38 V, respectively. Observation by UV-vis-near IR spectroelecrochemistry indicated that ZnPH was first oxidized to ZnPH+ and that the second oxidation renders rapid intramolecular chemical reaction to form isoporphyrin, ZnIP. FT-IR spectroelecrochemical study revealed the stepwise intramolecular attack by the oxygen of the amide group to the meso carbon of the porphyrin dication and the formation of the endogenous isoporphyrin. Further oxidation of the isoporphyrin probably resulted in slow ring-opening and decomposition. Addition of a sterically hindered organic base, 2,6-lutidine, rapidly caused ZnPH+ deprotonation to form ZnIP. EPR spectrum of ZnIP was observed and shown a free radical formation. ZnIP could be oxidized to ZnIP+ at the formal potential of +0.96 V. This is the first time that an isoporphyrin radical is observed. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
| Externí odkaz: |
|