Mechanism of the electrochemical reduction of tetrazolium blue in non-ionic micelles

Synthesis, spectroscopic and electrochemical studies on bis-[1,3-substituted (Cl, Br) phenyl-5-phenyl formazanato]nickel(II) complexes

In this study, new 1:2 Ni complexes of 1,3-substituted phenyl-5-phenylformazans were synthesized with -Cl, -Br substituents in the o-, m-, p-positions of the 1-phenyl ring and -NO2 group in the m-position of the 3-phenyl ring. Their structures were elucidated and spectral behaviors were investigated with the use of elemental analysis, GC-Mass, 1H NMR, 13C NMR, FTIR, UV-vis spectra. Furthermore electrochemical properties such as number of electrons transferred (n), diffusion coefficients (D) and possible reaction mechanism of the compounds were determined with the use of cyclic voltammetry, ultramicrodisc electrode and chronoamperometry. The relation between their absorption properties and electrochemical properties was examined. A linear correlation was obtained between Hammett substituent coefficients with lambda(max) values.

Radical intermediates in the redox reactions of tetrazolium salts in aprotic solvents (cyclovoltammetric, EPR and UV-VIS study)

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.