2-Mercaptoethanol

2-Mercaptoethanol (also β-mercaptoethanol, BME, 2BME, 2-ME or β-met) is the chemical compound with the formula HOCH2CH2SH. ME or βME, as it is commonly abbreviated, is used to reduce disulfide bonds and can act as a biological antioxidant by scavenging hydroxyl radicals (amongst others). 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.

2-Mercaptoethanol
Names
Preferred IUPAC name
2-Sulfanylethan-1-ol[1]
Other names
2-Mercaptoethan-1-ol
2-Hydroxy-1-ethanethiol
β-Mercaptoethanol
Thioglycol
Beta-merc
Identifiers
CAS Number
3D model (JSmol)
3DMet
Beilstein Reference
 773648
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard 100.000.422
EC Number
  • 200-464-6
Gmelin Reference
 1368
KEGG
MeSH Mercaptoethanol
PubChem CID
RTECS number
  • KL5600000
UNII
UN number 2966
InChI
  • InChI=1S/C2H6OS/c3-1-2-4/h3-4H,1-2H2 Y
    Key: DGVVWUTYPXICAM-UHFFFAOYSA-N Y
SMILES
  • OCCS
Properties
Chemical formula
 C2H6OS
Molar mass 78.13 g·mol−1
Odor Disagreeable, distinctive
Density 1.114 g/cm3
Melting point −100 °C (−148 °F; 173 K)
Boiling point 157 °C; 314 °F; 430 K
log P −0.23
Vapor pressure 0.76 hPa (at 20 °C);
4.67 hPa (at 40 °C)
Acidity (pKa) 9.643
Basicity (pKb) 4.354
Refractive index (nD)
 1.4996
Hazards
GHS labelling:
Pictograms
Signal word
 Danger
Hazard statements
 H301, H310, H315, H317, H318, H330, H410
Precautionary statements
 P260, P273, P280, P284, P301+P310, P302+P350
Flash point 68 °C (154 °F; 341 K)
Explosive limits 18%
Lethal dose or concentration (LD, LC):
244 mg/kg (oral, rat)[2]
150 mg/kg (skin, rabbit)[2]
Related compounds
Related compounds
 Ethylene glycol
1,2-Ethanedithiol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Production

2-Mercaptoethanol is manufactured industrially by the reaction of ethylene oxide with hydrogen sulfide. Thiodiglycol and various zeolites catalyze the reaction.[3]

Reactions

2-Mercaptoethanol reacts with aldehydes and ketones to give the corresponding oxathiolanes.[4] This makes 2-mercaptoethanol useful as a protecting group, giving a derivative whose stability is between that of a dioxolane and a dithiolane.[5]

Applications

Reducing proteins

Some proteins can be denatured by 2-mercaptoethanol, which cleaves the disulfide bonds that may form between thiol groups of cysteine residues. In the case of excess 2-mercaptoethanol, the following equilibrium is shifted to the right:

RS–SR + 2 HOCH2CH2SH ⇌ 2 RSH + HOCH2CH2S–SCH2CH2OH

By breaking the S-S bonds, both the tertiary structure and the quaternary structure of some proteins can be disrupted.[6] 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 (DTT) is generally more used especially in SDS-PAGE. DTT is also a more powerful reducing agent with a redox potential (at pH 7) of −0.33 V, compared to −0.26 V for 2-mercaptoethanol.[7]

2-Mercaptoethanol is often used interchangeably with dithiothreitol (DTT) or the odorless tris(2-carboxyethyl)phosphine (TCEP) 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.[8][9]

Preventing protein oxidation

2-Mercaptoethanol and related reducing agents (e.g., DTT) 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.[10]

Denaturing ribonucleases

2-Mercaptoethanol is used in some RNA isolation procedures to eliminate ribonuclease released during cell lysis. Numerous disulfide bonds make ribonucleases very stable enzymes, so 2-mercaptoethanol is used to reduce these disulfide bonds and irreversibly denature the proteins. This prevents them from digesting the RNA during its extraction procedure.[11]

Deprotecting carbamates

Some carbamate protecting groups such as carboxybenzyl (Cbz) or allyloxycarbonyl (alloc) can be deprotected using 2-mercaptoethanol in the presence of potassium phosphate in dimethylacetamide.[12]

Safety

2-Mercaptoethanol is considered toxic, causing irritation to the nasal passageways and respiratory tract upon inhalation, irritation to the skin, vomiting and stomach pain through ingestion, and potentially death if severe exposure occurs.[13]

See also

References
  1. Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. p. 697. doi:10.1039/9781849733069-FP001. ISBN 978-0-85404-182-4. The prefixes ‘mercapto’ (–SH), and ‘hydroseleno’ or selenyl (–SeH), etc. are no longer recommended.
  2. 2-Mercaptoethanol
  3. Roy, Kathrin-Maria (2005). "Thiols and Organic sulphides". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a26_767.
  4. "1,3-Dithiolanes, 1,3-Dithianes". Organic Chemistry Portal. Archived from the original on 17 May 2008. Retrieved 27 May 2008.
  5. Sartori, Giovanni; Ballini, Roberto; Bigi, Franca; Bosica, Giovanna; Maggi, Raimondo; Righi, Paolo (2004). "Protection (and Deprotection) of Functional Groups in Organic Synthesis by Heterogeneous Catalysis". Chem. Rev. 104 (1): 199–250. doi:10.1021/cr0200769. PMID 14719975.
  6. "2-Mercaptoethanol". Chemicalland21.com. Archived from the original on 2006-10-05. Retrieved 8 October 2006.
  7. Aitken CE; Marshall RA, Puglisi JD (2008). "An oxygen scavenging system for improvement of dye stability in single-molecule fluorescence experiments". Biophys J. 94 (5): 1826–35. Bibcode:2008BpJ....94.1826A. doi:10.1529/biophysj.107.117689. PMC 2242739. PMID 17921203.
  8. Yeh, J. I. (2009) "Additives and microcalorimetric approaches for optimization of crystallization" in Protein Crystallization, 2nd Edition (Ed: T. Bergfors), International University Line, La Jolla, CA. ISBN 978-0-9720774-4-6.
  9. Stevens R.; Stevens L.; Price N.C. (1983). "The Stabilities of Various Thiol Compounds used in Protein Purifications". Biochemical Education. 11 (2): 70. doi:10.1016/0307-4412(83)90048-1.
  10. Verduyn, C; Van Kleef, R; Frank, J; Schreuder, H; Van Dijken, J. P.; Scheffers, W. A. (1985). "Properties of the NAD(P)H-dependent xylose reductase from the xylose-fermenting yeast Pichia stipitis". The Biochemical Journal. 226 (3): 669–77. doi:10.1042/bj2260669. PMC 1144764. PMID 3921014.
  11. Nelson, David R.; Lehninger, Albert L; Cox, Michael (2005). Lehninger principles of biochemistry. New York: W.H. Freeman. pp. 148. ISBN 0-7167-4339-6.
  12. Scattolin, Thomas; Gharbaoui, Tawfik; Chen, Cheng-yi (2022). "A Nucleophilic Deprotection of Carbamate Mediated by 2-Mercaptoethanol". Organic Letters. 24 (20): 3736–3740. doi:10.1021/acs.orglett.2c01410. PMID 35559611. S2CID 248776636.
  13. "Material Safety Data Sheet". JT Baker. Retrieved 31 July 2011.
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