Sankei Co. Ltd., Shiromi, Chuou-Ku, Osaka, Japan.
Department of Life Science and Technology, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo, Japan.
PLoS One. 2021 May 26;16(5):e0252079. doi: 10.1371/journal.pone.0252079. eCollection 2021.
The present study identified the active radical species in acidic sodium chlorite and investigated the feasibility of quantifying these species with the diethylphenylenediamine (DPD) method. Electron spin resonance (ESR) spectroscopy was used to identify the active species generated in solutions containing sodium chlorite (NaClO2). The ESR signal was directly observed in an acidified sodium chlorite (ASC) aqueous solution at room temperature. This ESR signal was very long-lived, indicating that the radical was thermodynamically stable. The ESR parameters of this signal did not coincide with previously reported values of the chlorine radical (Cl●) or chlorine dioxide radical (O = Cl●-O and O = Cl-O●). We refer to this signal as being from the chloroperoxyl radical (Cl-O-O●). Quantum chemical calculations revealed that the optimal structure of the chloroperoxyl radical is much more thermodynamically stable than that of the chlorine dioxide radical. The UV-visible spectrum of the chloroperoxyl radical showed maximum absorbance at 354 nm. This absorbance had a linear relationship with the chloroperoxyl radical ESR signal intensity. Quantifying the free chlorine concentration by the DPD method also revealed a linear relationship with the maximum absorbance at 354 nm, which in turn showed a linear relationship with the chloroperoxyl radical ESR signal intensity. These linear relationships suggest that the DPD method can quantify chloroperoxyl radicals, which this study considers to be the active species in ASC aqueous solution.
本研究鉴定了酸性亚氯酸钠中的活性自由基种类，并探讨了用二乙基对苯二胺（DPD）法定量这些种类的可行性。电子自旋共振（ESR）光谱用于鉴定含有亚氯酸钠（NaClO2）的溶液中产生的活性物质。在室温下，可直接在酸化的亚氯酸钠（ASC）水溶液中观察到 ESR 信号。该 ESR 信号具有很长的寿命，表明自由基在热力学上是稳定的。该信号的 ESR 参数与先前报道的氯自由基（Cl●）或二氧化氯自由基（O = Cl●-O 和 O = Cl-O●）的值不相符。我们将此信号称为过氯酰基自由基（Cl-O-O●）。量子化学计算表明，过氯酰基自由基的最佳结构比二氧化氯自由基在热力学上稳定得多。过氯酰基自由基的紫外-可见光谱在 354nm 处显示最大吸收。该吸光度与过氯酰基自由基 ESR 信号强度呈线性关系。通过 DPD 法定量游离氯浓度也显示出与 354nm 处最大吸收的线性关系，而 354nm 处最大吸收又与过氯酰基自由基 ESR 信号强度呈线性关系。这些线性关系表明，DPD 法可以定量过氯酰基自由基，本研究认为过氯酰基自由基是 ASC 水溶液中的活性物质。
