Structural Properties of 4-Substituted Phenols Capable of Proton-Coupled Electron Transfer to Superoxide
Structural Properties of 4-Substituted Phenols Capable of Proton-Coupled Electron Transfer to Superoxide
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能够质子耦合电子转移到超氧化物的 4-取代苯酚的结构性质
DOI：
10.20431/2349-0403.0301002
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
B. Uno
中科院分区：
文献类型：
--
作者：
Tatsushi Nakayama;B. Uno
基于电化学和电子自旋共振（ESR）光谱测量和密度泛函理论计算，研究了4-取代酚类化合物对超氧阴离子（O2）的质子耦合电子转移（PCET）的结构性质.虽然酚类的质子和电子供给能力被认为是PCET反应中的重要因素，但4-取代单酚与O2 ·−反应的主要机理是质子转移途径，该途径与电子取代基效应无关。相反，除了对苯二酚之外，4-氨基苯酚的存在明显地影响可逆的O2/O2 ·−氧化还原对;相关的PCET反应从4-氨基苯酚到O2 ·−发生，在氧化还原系统中产生稳定的中间体自由基。从ESR光谱测量结果推断对苯醌亚胺自由基的产生。B3 LYP/PCM/6-31+G（d，p）计算表明，O2 -清除反应包括质子从4-氨基苯酚转移到O2 ·−生成HO 2，然后通过一步协同PCET反应生成对苯醌亚胺自由基和H2 O2. 4-氨基苯酚的结构性质在O2清除PCET反应中是重要的; 4-氨基苯酚的特征在于由涉及两个质子和两个电子的双电子氧化还原系统，类似于醌-氢醌氧化还原系统。
The structural properties of 4-substituted phenols capable of proton-coupled electron transfer (PCET) to superoxide (O2 ) were investigated on the basis of electrochemical and electron spin resonance (ESR) spectral measurements and supported by density functional theory calculations. Although the proton and electron donating abilities of phenols are considered to be important factors in PCET reactions, the major mechanism for the reactions between 4-substitued monophenols and O2 •− is the proton-transfer pathway that is independent of the electronic substituent effect. Conversely, the presence of 4-aminophenol in addition to p-hydroquinone distinctly affects the reversible O2/O2 •− redox pair; the associated PCET reaction occurs from the 4-aminophenol to O2 •− to give a stable intermediate radical in the redox system. The generation of p-benzoquinone imine radical was inferred from the results obtained from ESR spectral measurements. B3LYP/PCM/6-31+G(d,p) calculations indicate that the O2 -scavenging reaction involves a primary proton transfer from 4-aminophenol to O2 •− to give HO2 , followed by a one-step concerted PCET reaction to yield p-benzoquinone imine radical and H2O2. The structural properties of 4-aminophenol are important in the O2 -scavenging PCET reaction; 4-aninophenol is characterized by a electronic redox system involving two protons and two electrons, similar to the quinone–hydroquinone redox system.