Self-catalysis by catechols and quinones during heterogeneous electron transfer at carbon electrodes
Self-catalysis by catechols and quinones during heterogeneous electron transfer at carbon electrodes
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DOI：
10.1021/ja000227u
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发表时间：
2000-07-19
影响因子：
15
通讯作者：
McCreery, RL
中科院分区：
文献类型：
--
作者：
DuVall, SH;McCreery, RL
研究了邻苯二酚在玻碳电极上的非均相电子转移动力学。电极制备得到的GC表面的氧化物或吸附的杂质，表现出较强的吸附多巴胺（DA）和相关的儿茶酚的水平低。相反，修饰的GC与有机单层抑制DA吸附，并在许多情况下，防止电子转移。通过儿茶酚吸附所观察到的电子转移，可以得出结论，吸附层的儿茶酚作为电催化剂的溶液相氧化还原组分。物理吸附或化学吸附的几种醌，包括杜醌，蒽醌，和多巴胺本身的单分子膜，对多巴胺的氧化和还原是催化的，但硝基苯基，三氟甲基苯基，和亚甲蓝单分子膜严重抑制电子转移。抑制的大小受表面和氧化还原体系之间的静电吸引或排斥的影响，但控制电子转移动力学的主要因素不是静电的起源。最合理的机制是通过吸附的醌的"自催化"，其在电子转移到溶液中的氧化还原对期间保持吸附。结果是不一致的氧化还原调解机制，涉及吸附和溶液醌对之间的氧化还原交叉反应。吸附和溶液中的醌类之间的相互作用，在电子转移过程中出现催化的一个或多个步骤中的“方桉”的氢醌/醌氧化还原系统的机制。这些结果解释了关于邻苯二酚和对苯二酚电化学的各种观察结果，并为醌电子转移机制提供了更基本的见解。
Heterogeneous electron transfer kinetics for several catechols were examined on glassy carbon (GC) electrodes in aqueous solution. Electrode preparations yielded GC surfaces with low levels of oxides or adsorbed impurities, which exhibited strong adsorption of dopamine (DA) and related catechols. Conversely, modification of GC with an organic monolayer suppressed DA adsorption and in many cases prevented electron transfer. By relating catechol adsorption to observed electron transfer, it was concluded that an adsorbed layer of catechol acts as an electrocatalyst for solution-phase redox components. Physisorbed or chemisorbed monolayers of several quinones, including duroquinone, anthraquinone, and dopamine itself, are catalytic toward dopamine oxidation and reduction, but nitrophenyl, trifluoromethylphenyl, and methylene blue monolayers severely inhibit electron transfer. The magnitude of inhibition was affected by electrostatic attraction or repulsion between the surface and the redox system, but the major factor controlling electron-transfer kinetics is not electrostatic in origin. The most plausible mechanism is "self-catalysis" by an adsorbed quinone, which remained adsorbed during electron transfer to a redox couple in solution. The results are inconsistent with a redox mediation mechanism involving a redox cross-reaction between adsorbed and solution quinone couples. An interaction between the adsorbed and solution quinone species during electron transfer appears to catalyze one or more of the steps in the "scheme of squares" mechanism for hydroquinone/quinone redox systems. The results explain a variety of observations about catechol and hydroquinone electrochemistry, as well as provide more fundamental insights into quinone electron-transfer mechanisms.