关键词: 大黄素, 二聚, 现场红外光谱电化学, 循环伏吸法, 导数循环伏吸法

Abstract:

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.

Key words: emodin, dimerization, in situ FT–IR spectroelectrochemistry, cyclic voltabsorptometry (CVA), derivative cyclic voltaborptometry (DCVA)