L

L-Cysteine

IUPAC: (2R)-2-amino-3-sulfanylpropanoic acid

C3H7NO2S Organic Compounds CAS 52-90-4
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Quick Reference
Formula / NotationC3H7NO2S
CAS Number52-90-4
Molecular Weight121.16
Melting Point240 dec °C
Solubility277000 mg/L (at 25 °C)
AppearanceColorless or white solid; [HSDB] Colorless crystalline solid; [Sigma-Aldrich MSDS]
Also Known As(2R)-2-amino-3-sulfanylpropanoic acid; cysteine; 52-90-4; Cystein; Thioserine; Half-cystine; (R)-2-Amino-3-mercaptopropanoic acid; L-(+)-Cysteine; beta-Mercaptoalanine; L-Cystein
CategoryOrganic Compounds

What is L-Cysteine?

L-cysteine is an optically active form of cysteine having L-configuration. It has a role as a flour treatment agent, an EC 4.3.1.3 (histidine ammonia-lyase) inhibitor and a human metabolite. It is a cysteine, a L-alpha-amino acid, a serine family amino acid and a proteinogenic amino acid. It is a conjugate base of a L-cysteinium. It is a conjugate acid of a L-cysteinate(1-). It is an enantiomer of a D-cysteine. It is a tautomer of a L-cysteine zwitterion.

Formula & Notation

C3H7NO2S

IUPAC Name: (2R)-2-amino-3-sulfanylpropanoic acid

Other Names / Synonyms: (2R)-2-amino-3-sulfanylpropanoic acid; cysteine; 52-90-4; Cystein; Thioserine; Half-cystine; (R)-2-Amino-3-mercaptopropanoic acid; L-(+)-Cysteine; beta-Mercaptoalanine; L-Cystein

Properties & Characteristics

Appearance: Colorless or white solid; [HSDB] Colorless crystalline solid; [Sigma-Aldrich MSDS]. Molecular formula: C3H7NO2S. Molecular weight: 121.16 g/mol. Melting point: 240 dec °C. Solubility: 277000 mg/L (at 25 °C). Vapor pressure: 0.00000207 [mmHg]. LogP: -2.5.

Physical Data

PropertyValue
Melting Point240 dec °C
Molecular Weight121.16
Solubility277000 mg/L (at 25 °C)
AppearanceColorless or white solid; [HSDB] Colorless crystalline solid; [Sigma-Aldrich MSDS]

Uses & Applications

Used as an industrial feedstock, solvent, pharmaceutical intermediate, flavoring agent, or chemical building block.

Safety Information

Flammable or irritant. Many organic compounds are flammable liquids or vapours. Keep away from ignition sources. Consult SDS for specific hazard data.

Always consult the SDS/MSDS before handling any chemical. This information is for educational purposes only.

Key Facts

Term L-Cysteine
Formula C3H7NO2S
CAS Number 52-90-4
Molecular Weight 121.16
Synonyms (2R)-2-amino-3-sulfanylpropanoic acid; cysteine; 52-90-4; Cystein; Thioserine; Half-cystine; (R)-2-Amino-3-mercaptopropanoic acid; L-(+)-Cysteine; beta-Mercaptoalanine; L-Cystein

Frequently Asked Questions

L-cysteine is an optically active form of cysteine having L-configuration. It has a role as a flour treatment agent, an EC 4.3.1.3 (histidine ammonia-lyase) inhibitor and a human metabolite. It is a cysteine, a L-alpha-amino acid, a serine family amino acid and a proteinogenic amino acid. It is a conjugate base of a L-cysteinium. It is a conjugate acid of a L-cysteinate(1-). It is an enantiomer of a D-cysteine. It is a tautomer of a L-cysteine zwitterion.

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Editorial standards: Chemical data is sourced from peer-reviewed literature, CAS Registry, NIST WebBook, and PubChem. Safety information reflects guidance from OSHA, ECHA, and IAEA. For educational purposes only — always consult official SDS documentation and qualified professionals before handling chemicals.