2-Mercaptoethanol
2-Mercaptoethanol is the organosulfur compound with the formula HOCH2CH2SH. ME or βME, as it is commonly abbreviated, is used to reduce disulfide bonds. It is widely used because the hydroxyl group confers solubility in water and lowers the volatility. Due to its diminished vapor pressure, its odor, while unpleasant, is less objectionable than related thiols.
Production
2-Mercaptoethanol is manufactured industrially by the reaction of ethylene oxide with hydrogen sulfide. Thiodiglycol and various zeolites catalyze the reaction.Reactions
2-Mercaptoethanol cleaves disulfide bonds.2-Mercaptoethanol reacts with aldehydes and ketones to give the corresponding oxathiolanes. This makes 2-mercaptoethanol useful as a protecting group, giving a derivative whose stability is between that of a dioxolane and a dithiolane.
Like most alkylthiols, it adds to Michael acceptors such as acrylonitrile.
Applications
Reducing proteins
Some proteins are denatured by 2-mercaptoethanol. In the case of excess 2-mercaptoethanol, the following equilibrium is shifted to the right:By breaking the S-S bonds, both the tertiary structure and the quaternary structure of some proteins can be disrupted. Because of its ability to disrupt the structure of proteins, it was used in the analysis of proteins, for instance, to ensure that a protein solution contains monomeric protein molecules, instead of disulfide linked dimers or higher order oligomers. However, since 2-mercaptoethanol forms adducts with free cysteines and is somewhat more toxic, dithiothreitol is generally more used especially in SDS-PAGE. DTT is also a more powerful reducing agent with a redox potential of −0.33 V, compared to −0.26 V for 2-mercaptoethanol.
2-Mercaptoethanol is often used interchangeably with dithiothreitol or the odorless trisphosphine in biological applications.
Although 2-mercaptoethanol has a higher volatility than DTT, it is more stable: 2-mercaptoethanol's half-life is more than 100 hours at pH 6.5 and 4 hours at pH 8.5; DTT's half-life is 40 hours at pH 6.5 and 1.5 hours at pH 8.5.
2-Mercaptoethanol and related reducing agents are often included in enzymatic reactions to inhibit the oxidation of free sulfhydryl residues, and hence maintain protein activity. It is often used in enzyme assays as a standard buffer component.