TMB Hydrochloride

TMB, also known as 3,3',5,5'-Tetramethylbenzidine dihydrochloride dihydrate, is an aromatic amine that plays a crucial role in the oxidation process of heme peroxidases. Its interaction with the higher oxidation states of compounds I and II leads to its conversion into a radical cation, forming a charge-transfer complex when combined with the unoxidized compound. This complex exhibits an absorption peak at 652 nm with a molar absorptivity (ε) of 39,000.
Interestingly, TMB can further undergo oxidation to its completely oxidized form, known as diimine. This conversion occurs through two sequential one-electron oxidations of TMB. The diimine species, characterized by its absorption peak at 450 nm and ε value of 59,000, is formed when one mole of TMB is oxidized.
It is worth noting that the stoichiometry of this oxidation process involves either the formation of 0.5 moles of the charge transfer complex (with a maximum absorbance at 652 nm) or the production of 1 mole of diimine (with a maximum absorbance at 450 nm) per mole of hydroperoxide reduced by the peroxidase enzyme.
In summary, TMB acts as a reducing co-substrate, undergoing one-electron oxidation to form a radical cation and subsequently forming a charge-transfer complex or diimine, depending on the extent of oxidation. These transformations are achieved through the interaction with heme peroxidases and play a vital role in the enzymatic reduction of hydroperoxide.