摘要
本文研究了由Cu(Ⅱ)(PlC)_2、分子氧和碱构成的体系中醇类选择氧化生成相应醛、酮的反应机理,研究结果表明,该催化体系可作为半乳糖氧化酶催化作用的化学模型。根据原位电子光谱,ESR波谱对催化体系的考察,证明催化反应诱导期是Cu(Ⅱ)→Cu(Ⅰ)状态的转变过程,催化过程存在Cu(Ⅱ)/Cu(Ⅰ)价态的循环。相同配体的Cu(Ⅰ)和Cu(Ⅱ)络合物催化氧化反应的性能差异支持了上述结果。动力学研究表明,催化反应符合酶催化米氏方程的一般规律,根据以上结果,提出了一个由底物、双氧、Cu(Ⅱ)络合物形成的三元复合物中间物种的分解而生成产物醛、酮和H_2O_2的反应机理。
A new chemical model system, Cu (Ⅱ) ( PIC ) 2, has been employed to simulate the copper ( Ⅱ ) metalloenzyme, galactose oxidase. This model system has been studied for its reaction mechanism in the catalytic oxidation of benzyl alcohol in an alkaline medium at room temperature. Hydrogen peroxide which was detected in the reaction mixture was found to inhibit the oxidation reaction. The in-situ electronic spectral and ESR studies in the simulated system indicate that the process taking place in the induction period is the conversion of Cu ( Ⅱ )→Cu ( Ⅰ ). This conversion between copper ( Ⅱ ) and copper (Ⅰ ) species forms cycles and is shown to be essential for the catalytic process. That the copper (Ⅱ ) species must be converted to copper (Ⅰ ) species in the induction period is also indicated by the difference in the oxidation of benzyl alcohol catalyzed by Cu (Ⅱ ) (PIC)2 and by H[Cu ( Ⅰ ) (PIC ) 2]. The initial rate of the catalytic oxidation of PhCH2OH was found to be first order for the copper (Ⅱ ) complex, first order for the substrate at low concentration of PhCH2OH, and zero order in the substrate at high concentration of PhCH2OH. The kinetic study is in favor of the formation of an active intermediate complex: copper (Ⅱ )-alkoxide-superoxide species. Based on the above studies, a mechanism for the catalytic oxidation of PhCH2OH is suggested for this model system for GOase.
出处
《分子催化》
EI
CAS
CSCD
1991年第3期248-256,共9页
Journal of Molecular Catalysis(China)
基金
国家自然科学基金
