铜(Ⅱ)及其多胺螯合物催化抗坏血酸有氧氧化动力学

抗坏血酸与自由钢(Ⅱ)及其多胺螯合物不发生直接的氧化还原反应。铜(Ⅱ)与抗坏血酸有络合作用。螯合齿数大于2的铜(Ⅱ)-多胺螯合物对抗坏血酸的有氧氧化无催化活性。当配位数为2时, 铜(Ⅱ)-乙二胺的1:1螯合物的催化反应符合酶催化动力学。自由铜(Ⅱ)催化反应对铜(Ⅱ)及抗坏血酸均显一级。实验结果说明钢(Ⅱ)在催化抗坏血酸有氧氧化时, 只能有2个配位位置被占据。其它位置必须是空位或容易被取代。实验事实支持三元络合物形成的机制。

KINETICS OF THE AEROBIC OXIDATION OF ASCORBIC ACID CATALYZED BY Cu (Ⅱ) AND ITS POLYAMINE CHELATES

The kinetics of aerobic oxidation of ascorbic acid(H_2A) catalyzed by Cu(Ⅱ) and its polyamine chelates, of which chelate number vary from 2 to 5, was stu- died,The chelating agents used were ethylenediamine(en), diethylenetriamine(dien), triethylenetetramine(trien) and tetraethylenepentamine(tetren). The pH value was maintained constant by an automatic titrator without using buffer. The results showed that Cu(Ⅱ) could form a complex with ascorbate, however they did not react directly. Cu(Ⅱ) and Cu(Ⅱ)(en) did not react directly. Cu(Ⅱ) and Cu(Ⅱ)(en) did not change their valence during the catalytic processes. The kinetic determination showed that Cu(Ⅱ)(dien), Cu(Ⅱ)(trien), Cu(Ⅱ)(tetren) and Cu(Ⅱ)(en)_2, of which chelate number are larger than 2 were catalytically inactive. For Cu(Ⅱ)(en) catalyzed reaction, the rate was first order with respect to Cu(Ⅱ)(en) and conformed to the Michaelis-Menten equation with respect to ascorbate. For free Cu(Ⅱ) catalyzed reaction, the rate was first order with respect to both Cu(Ⅱ) and ascorbate.A mechanism via a ternary complex, Cu(Ⅱ)HAO_2, was proposed. It was suggested that Cu(Ⅱ) and Cu(Ⅱ)(en) undergo the same initial step in the catalytic processes.