肾上腺素氧化反应的研究——氧化反应动力学和机理以及自由基中间体

RESEARCH ON THE OXIDATION OF ADRENALINE——KINETICS AND MECHANISM OF THE OXIDATION REACTION AND THE RADICAL INTERMIDATE

用紫外吸收光谱法结合计算机模拟研究了肾上腺素(Adjn)在Cu(Ⅱ)离子催化下,用H_2O_2氧化产生肾上腺素红(Adom)的反应动力学,考查了反应的速率随体系中肾上腺素的初始浓度,Cu(Ⅱ)离子浓度和H_2O_2浓度的变化情况。在流动法或添加自由基稳定剂的条件下,利用顺磁共振法检测丁肾上腺素自氧化,光氧化和Cu(Ⅱ)离子催化H_2O_2氧化产生的半醌自由基。考查了Cu(Ⅱ)离子催化下自由基的相对浓度随反应条件的变化情况。在反应动力学和顺磁共振实验的基础上所提出的可能的反应机理,半定量地解释此反应动力学实验结果和顺磁共振实验中的自由基行为。

Using the UV absorption spectrometry in connection with computer simulation,the oxidation reaction kinetics of adrenaline forming adrenoehrome, with H_2O_2 in Cu(Ⅱ) existing as a catalyst had been studied. Since there is some overlap in the spectra of adrenaline and adrenochrome (Fig.1), the double wave-length method was used. The order of this reaction with respect to adrenaline is 1/2. The corresponding apparent reaction rate constants are independent of the initial concentration [Adin]_0 of adrenline (Table 1), hut depend on the concentrations of Cu(Ⅱ), H_2O_2 and H^+ in accordance with equations (1a) and (1b). The experimental values kE and regression calculated values kC of the apparent rate constants k(app) under different experimental conditions are listed in the last two rows of Table 2, respectively. The linear correlation of kE and kC is shown in Fig2. Examining this figure, it can be said that the regression calculated values are satisfiable. In order to propose a reasonable probable mechanism of this reaction, by means of the electron paramagnetic resonance method, the radical intermidate was examined under the flow condition or sometimes a radical stabilizer…Zn(Ⅱ) was added. The ESR spectra of the radical were obtained through various oxidation reaction ways of adrenaline. The different oxidation reaction ways correspond to autoxidation(Fig.3), photoxidation (Fig.4) and Cu(Ⅱ) catalytic oxidation with H_2O_2 (Fig.5). For the least oxidation way the radical stabilizer Zn(Ⅱ) was added. In this way, the peak heights (h) of ESR spectra in various experiment conditions were studied in more detail (Fig.6 and Table 3). The h ought to be dependent on the [Adin],[Cu(Ⅱ)] and [H_2O_2], as shown in equations (2a-c). The linear correlation between the experimental values(hE)and calculated values (hC) of the peak hights is fine (Fig.7).For eompareing, in the Cu(Ⅱ)+Zn(Ⅱ) system with and without adrenaline, the ESR spectra of Cu(Ⅱ) were eximined (Fig.8). According to the results of both the oxidation reaction kinetic experiment and radical ESR spectra, the probable mechanism has been suggested. Then the kinetics law and the related radical ESR spectra may be explained semi-quantitatively.