大黄素的电化学氧化还原机理研究

本文利用循环伏安法(CV)、红外光谱循环伏吸法(CVA)和导数循环伏吸法(DCVA)研究大黄素(Q)在乙腈溶剂中的电子转移机理.Q的还原过程中阴离子自由基Q^?-会结合中性分子Q生成二聚物Q₂^?-.Q₂^?-在更负的电位下进一步还原为Q₂^2-.当扫描范围为-0.2 ~ -2.0 V时，经过一个循环伏安过程，在扫描结束物质并没有回到反应物Q，而是Q₂^2-. Q₂^2-会继续发生电化学反应，经历两步一电子过程，分别生成Q₂^3-. 和Q₂^4-.，对应CV图中峰C₃和C₄.当扫描范围扩大至1.0~-2.0 V时，在更正的电位下，观察到两个新的氧化峰A₁和A₂，该范围内的三圈扫描结果表明，在扫描结束物质重新氧化回到Q.当扫描范围缩小至0.3 ~ -1.4 V，A2峰随着扫描圈数的增加而增大，与A2峰对应的氧化产物Q₂^?-在溶液中不断积累.A1峰对应于Q₂^?-氧化回到Q.

Study on the Electrochemical Redox Mechanism of Emodin

The electrochemical reduction of emodin (Q) has been investigated in acetonitrile by cyclic voltammetry (CV), IR spectroelectrochemistry cyclic voltabsorptometry (CVA) and derivative cyclic voltabsorptometry (DCVA) techniques. It was found that anion radical Q^•− interacted with neutral Q to form dimer Q₂^•− which was further reduced to Q₂²⁻ at more negative potentials. A two-step one-electron process involving electrochemical reductions of Q₂²⁻ to form Q₂³⁻ in the first step and Q₂⁴⁻ in the second step, corresponding to the two cathodic peaks of C₃ and C₄ in CV curves was confirmed. When the scan range was between 1.0 and -2.0 V, there were two new anodic peaks (A₁, A₂) formed at more positive potentials. When the scan range was 0.3~-1.4 V, the current value of A₂ increased with the added scan cycles, indicating that Q₂^•− accumulated in the solution. The C₁ and C₂ peaks still appeared in the second and third scans in CV curves under the consecutive scans from 1.0 to -2.0 V, suggesting the regainer of Q after each potential cycle. And Q₂^•− would be oxidized to Q at the potential corresponding to A₁. As a result, the electrochemical redox mechanism of emodin has been proposed.