TMB dihydrochloride 3,3',5,5'-Tetramethylbenzidine dihydrochloride

3,3',5,5'-Tetramethylbenzidine dihydrochloride dihydrate (TMB) is an aromatic amine that undergoes oxidation by the higher oxidation states of heme peroxidases thereby serving as a reducing co-substrate. One electron oxidation of TMB results in a radical cation that creates a charge-transfer complex with the unoxidized compound. This charge transfer complex absorbs at 652 nm (? = 39,000). The completely oxidized form (diimine) absorbs at 450 nm (? = 59,000) and is formed by two sequential one-electron oxidations of TMB. Thus the stoichiometry of oxidation is 0.5 mole charge transfer complex (?max = 652 nm) or 1 mole of diimine (?max = 450 nm) formed (or TMB oxidized) per mole of hydroperoxide reduced by the peroxidase.