N,N,N',N'-Tetramethyl-p-phenylenediamine dihydrochloride

N,N,N',N'-Tetramethyl-p-phenylenediamine dihydrochloride (TMPD) is a redox-active aromatic amine compound, widely used in biochemical and analytical applications, particularly as a chromogenic redox indicator. TMPD is commonly used in redox titrations and biochemical assays. It is colorless in its reduced form and turns blue or purple (called Wurster's Blue) upon oxidation, indicating electron transfer activity. This makes it valuable for detecting the presence or activity of oxidases or cytochromes. TMPD serves as an artificial electron donor, particularly to cytochrome c oxidase (complex IV) in the mitochondrial electron transport chain. It's often used in combination with ascorbate to assess respiratory chain function. TMPD is used in colorimetric assays for peroxidase activity or other oxidoreductases, where a color change signals enzyme action.