Fast-scan voltammetry of cyclic nitroxide free radicals.
Fast-scan voltammetry of cyclic nitroxide free radicals.
复制标题
环状硝基氧自由基的快速扫描伏安法。
作者：
J. Baur;Shuai Wang;M. Brandt
采用碳纤维微电极快速扫描循环伏安法对环氮氧自由基（克里思）及其类似物进行了检测。克里思类似物在未改性碳纤维电极上的电化学行为被发现与它们在玻璃碳电极上的行为有很大不同。在用聚合物Nafion涂覆电极之后，电极表现出对克里思和4-氨基-TEMPO的增加的灵敏度。在Nafion涂层电极的氮氧化物的伏安图表明，氧化形式（氧铵离子）和自由基的形式有很大不同的迁移率通过聚合物涂层。对氮氧化物浓度变化的响应时间从裸电极（所有四种类似物）和修饰电极的4-羟基-TEMPO的亚秒到修饰电极的克里思和4-氨基-TEMPO的1-3秒不等。4-氨基-TEMPO的检测限在未修饰电极上为50 μM，在Nafion涂层碳纤维电极上为5 μM。Nafion修饰电极对克里思、4-羟基-TEMPO和4-氨基-TEMPO的灵敏度可以通过选择一个静息电位来提高，在该电位下，氮氧化物的氧代铵离子形式被预浓缩到Nafion膜中。利用快扫描循环伏安法和碳纤维修饰电极，可以监测两种氮氧自由基与抗坏血酸的反应。这项工作表明，在微电极上的快速扫描伏安法是一种灵敏的方法，可以用来跟踪溶液中的环氮氧自由基的反应。
Fast-scan cyclic voltammetry at carbon fiber microelectrodes is used to detect the cyclic nitroxide 2,2,6,6-tetramethylpiperidinyl-1-oxy free radical (TEMPO) and three analogs. The electrochemical behavior of the TEMPO analogs at unmodified carbon fiber electrodes is found to differ greatly from their behavior at glassy carbon electrodes. After the electrode is coated with the polymer Nafion, the electrodes exhibit increased sensitivity to TEMPO and 4-amino-TEMPO. Voltammograms of the nitroxides at Nafion-coated electrodes indicate that the oxidized form (oxoammonium ion) and the free radical form have greatly different mobilities through the polymeric coating. Response times to changes in nitroxide concentration vary from subsecond at bare electrodes (all four analogs) and 4-hydroxy-TEMPO at modified electrodes to 1-3 s for TEMPO and 4-amino-TEMPO at modified electrodes. The detection limit for 4-amino-TEMPO is 50 μM at an unmodified electrode and 5 μM at a Nafion-coated carbon fiber electrode. The sensitivity of the Nafion-modified electrode to TEMPO, 4-hydroxy-TEMPO, and 4-amino-TEMPO can be improved by choosing a resting potential at which the oxoammonium ion form of the nitroxide is preconcentrated into the Nafion film. Using fast-scan cyclic voltammetry and the modified carbon fiber electrodes, the reaction of two nitroxide free radicals with ascorbate can be monitored. This work shows that fast-scan voltammetry at microelectrodes is a sensitive method that can be used to follow reactions of cyclic nitroxide free radicals in solution.