Electron Paramagnetic Resonance for the Detection of Electrochemically Generated Hydroxyl Radicals: Issues Associated with Electrochemical Oxidation of the Spin Trap.
Electron Paramagnetic Resonance for the Detection of Electrochemically Generated Hydroxyl Radicals: Issues Associated with Electrochemical Oxidation of the Spin Trap.
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DOI：
10.1021/acsmeasuresciau.2c00049
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发表时间：
2023-02-15
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影响因子：
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通讯作者：
Macpherson, Julie V
中科院分区：
文献类型：
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作者：
Braxton, Emily;Fox, David J;Breeze, Ben G;Tully, Joshua J;Levey, Katherine J;Newton, Mark E;Macpherson, Julie V
为了检测硼掺杂金刚石 (BDD) 电极上水氧化产生的电化学羟基自由基 (HO·)，电子顺磁共振波谱 (EPR) 与自旋陷阱标记相结合是一种流行的技术。在这里，我们表明通过自旋陷阱电化学 (EC)-EPR 对水氧化产生的 H2O· 浓度进行定量是有问题的。这主要是由于自旋陷阱在比水弱的正电势下氧化，导致与OH·与自旋陷阱的溶液反应形成相同的自旋陷阱-OH·加合物。我们通过考虑 5,5-二甲基-1-吡咯啉 N-氧化物 (DMPO) 作为 OH·的自旋陷阱来说明这一点。酸性水溶液中 BDD 电极上的 DMPO 氧化发生在峰值电流电位为 +1.90 V（相对于 SCE）；水氧化电流在约 1 时开始迅速上升。 +2.3V 与 SCE 相比。 EC-EPR 光谱显示了由于自旋陷阱加合物 (DMPO-OH·) 的电势低于热力学预测值（对于水/H2O·）以及 DMPO 氧化区域的特征。令人惊奇的是，增加进入水氧化区域的电势显示出比电势处于DMPO氧化区域时更低的DMPO-OH·浓度。这种行为归因于 DMPO-OH· 的进一步氧化、电极表面污垢产物的产生以及气泡的形成。自由基清除剂（乙醇）和其他自旋陷阱，这里是 N-叔丁基-α-苯基硝酮、α-(4-吡啶基 N-氧化物)-N-叔丁基硝酮和 2-甲基-2-亚硝基丙烷二聚体，在 BDD 电极上也表现出不如水的电化学氧化信号。这种行为也使它们在预期应用中的使用变得复杂。
For the detection of electrochemically produced hydroxyl radicals (HO·) from the oxidation of water on a boron-doped diamond (BDD) electrode, electron paramagnetic resonance spectroscopy (EPR) in combination with spin trap labels is a popular technique. Here, we show that quantification of the concentration of HO· from water oxidation via spin trap electrochemical (EC)-EPR is problematic. This is primarily due to the spin trap oxidizing at potentials less positive than water, resulting in the same spin trap-OH· adduct as formed from the solution reaction of OH· with the spin trap. We illustrate this through consideration of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin trap for OH·. DMPO oxidation on a BDD electrode in an acidic aqueous solution occurs at a peak current potential of +1.90 V vs SCE; the current for water oxidation starts to rise rapidly at ca. +2.3 V vs SCE. EC-EPR spectra show signatures due to the spin trap adduct (DMPO-OH·) at potentials lower than that predicted thermodynamically (for water/HO·) and in the region for DMPO oxidation. Increasing the potential into the water oxidation region, surprisingly, shows a lower DMPO-OH· concentration than when the potential is in the DMPO oxidation region. This behavior is attributed to further oxidation of DMPO-OH·, production of fouling products on the electrode surface, and bubble formation. Radical scavengers (ethanol) and other spin traps, here N-tert-butyl-α-phenylnitrone, α-(4-pyridyl N-oxide)-N-tert-butylnitrone, and 2-methyl-2-nitrosopropane dimer, also show electrochemical oxidation signals less positive than that of water on a BDD electrode. Such behavior also complicates their use for the intended application.