Dithiothreitol (DTT) is the common name for a small-molecule redox reagent known as Cleland's reagent. DTT's oxidized form is a disulfide-bonded 6-membered ring. Its name derives from the four-carbon sugar, threose. DTT has an epimeric ('sister') compound, dithioerythritol (DTE).
DTT is an unusually strong reducing agent, owing to its high conformational propensity to form a six-membered ring with an internal disulfide bond. It has a redox potential of -0.33 V at pH 7. The reduction of a typical disulfide bond proceeds by two sequential thiol-disulfide exchange reactions and is illustrated below. The intermediate mixed-disulfide state is unstable (i.e., poorly populated) because the second thiol of DTT has a high propensity to close the ring, forming oxidized DTT and leaving behind a reduced disulfide bond. The reducing power of DTT is limited to pH values above ~7, since only the negatively charged thiolate form -S