Rapta P, Brezová V, Ceppan M, Melnik M, Bustin D, Stasko A
Faculty of Chemistry, Slovak Technical University, Bratislava.
Free Radic Res. 1994 Feb;20(2):71-82. doi: 10.3109/10715769409147505.
Tetrazolium Blue (TBCl2) and Nitrotetrazolium Blue (NTBCl2) cathodically reduced in non aqueous solvents form radicals with the center of unpaired electron on the tetrazolyl ring (TBH., NTBH.) as detected by EPR spectroscopy. After prolonged reduction, formazans (TBH2, NTBH2) are formed and are then further reduced to the nitro-centered anion radical (from NTBH2) and the azogroup-centered anion radical (from TBH2). The first cathodic peak in the cyclovoltammetric study in the region from -0.3 to -0.6 V vs. SCE (saturated calomel electrode) is irreversible and indicates an adsorption and diffusion process on the platinum and mercury electrodes. Formation of TBH+ and NTBH+ is assumed. The second peak, in the region from -0.8 to -1.3 V vs. SCE, is nearly reversible and coupled with the formation of TBH. and NTBH. radicals. UV-VIS spectra measured during the reduction show isosbestic points at the conversions: TB++-->TBH+, NTB++-->NTBH+; further, TBH+-->TBH2 and NTBH+-->NTBH2. The characteristic colours of the solutions observed can be used to characterise the reduction state of tetrazolium salts.
四唑蓝（TBCl2）和硝基四唑蓝（NTBCl2）在非水溶剂中阴极还原时会形成自由基，通过电子顺磁共振光谱检测发现，其未成对电子中心位于四唑环上（TBH·，NTBH·）。长时间还原后，会形成甲臜（TBH2，NTBH2），然后进一步还原为硝基中心阴离子自由基（来自NTBH2）和偶氮基团中心阴离子自由基（来自TBH2）。在循环伏安研究中，相对于饱和甘汞电极（SCE），在-0.3至-0.6V区域的第一个阴极峰是不可逆的，表明在铂电极和汞电极上存在吸附和扩散过程。推测形成了TBH+和NTBH+。第二个峰在相对于SCE为-0.8至-1.3V的区域，几乎是可逆的，且与TBH·和NTBH·自由基的形成相关。在还原过程中测量的紫外可见光谱在以下转化过程中显示等吸收点：TB++-->TBH+，NTB++-->NTBH+；此外，TBH+-->TBH2和NTBH+-->NTBH2。观察到的溶液特征颜色可用于表征四唑盐的还原状态。
