Cysteine
Athanor · official
C3H7NO2S · 121.16 g/mol
IUPAC name: (2R)-2-amino-3-sulfanylpropanoic acid
Also called L-cysteine, half-cystine
WarningHarmful if swallowed · Causes skin irritation · Causes serious eye irritation · May cause respiratory irritationNames and identifiers
- IUPAC name
- (2R)-2-amino-3-sulfanylpropanoic acid
- Synonyms
- L-cysteine, half-cystine, Cystein
+ 36 more
(R)-2-Amino-3-mercaptopropanoic acid, Thioserine, Half-cystine, L-(+)-Cysteine, L-Cystein, beta-Mercaptoalanine, (2R)-2-amino-3-sulfanylpropanoic acid, Cysteinum, L-Cys, cisteina, Half cystine, 2-Amino-3-mercaptopropionic acid, L-Alanine, 3-mercapto-, FREE CYSTEINE, Cisteinum, FEMA No. 3263, Cisteinum [Latin], NSC-8746, alpha-Amino-beta-thiolpropionic acid, L-2-Amino-3-mercaptopropionic acid, beta-Mercaptoalanine, L-, (2R)-2-amino-3-mercaptopropanoic acid, L Cysteine, alpha-Amino-beta-thiolpropionic acid, L-, AI3-26559, alpha-Amino-beta-mercaptopropanoic acid, L-, Propanoic acid, 2-amino-3-mercapto-, (R)-, CHEBI:17561, 2-Amino-3-mercaptopropanoic acid, (R)-, E 920, K848JZ4886, 2-amino-3-mercaptopropanoate, E920, DTXSID8022876, Cisteinum (Latin), (2R)-2-amino-3-mercaptopropanoate
- Molecular formula
- C3H7NO2S
- Empirical formula
- C3H7NO2S
- Molecular weight
- 121.16 g/mol
- Exact mass
- 121.01975
- CAS number
- 52-90-4
- PubChem CID
- 5862
- Canonical SMILES
- C(C(C(=O)O)N)S
- Isomeric SMILES
- C([C@@H](C(=O)O)N)S
- InChI
- InChI=1S/C3H7NO2S/c4-2(1-7)3(5)6/h2,7H,1,4H2,(H,5,6)/t2-/m0/s1
- InChIKey
- XUJNEKJLAYXESH-REOHCLBHSA-N
- Molfile
Names, InChI and the identifiers from PubChem, retrieved 2026-10-14.
Physical properties
- Appearance
- White crystals[1]
2 values
From Hazardous Substances Data Bank (HSDB), the most authoritative source here.
Value As written Source – Colorless crystals [1] Hazardous Substances Data Bank (HSDB)cites Lewis, R.J., Sr (Ed.). Hawley's Condensed Chemical Dictionary. 13th ed. New York, NY: John Wiley & Sons, Inc. 1997., p. 329 –shown White crystals [1] Hazardous Substances Data Bank (HSDB)cites Ashford, R.D. Ashford's Dictionary of Industrial Chemicals. London, England: Wavelength Publications Ltd., 1994., p. 255 - Solubility in water
- Water solubility (per g/100 g H2O): 28 g/100 mL of solution at 25 °C; 16 g/100 mL of solution at 20 °C[1]
- log P
- log Kow = -2.49[1]
Each value as its source reports it, with the source's number after it (listed under References). Where several sources report a property, the row shows the value most of them agree on, the rule the app uses; open the values to see every one.
Calculated
- Heavy atoms
- 7
- Rings
- 0
- Aromatic rings
- 0
- Fraction sp³ carbons (Fsp3)
- 0.67
- H-bond donors
- 3
- H-bond acceptors
- 3 computed here · PubChem 4
- Rotatable bonds
- 2
- TPSA (Ų)
- 63.3 computed here · PubChem 64.3
- Formal charge
- 0
- XLogP3
- -2.5 PubChem
- Complexity
- 75 PubChem
- Stereocenters
- 1 definedCIP: C3: R
- Double-bond geometry
- None specified
- Point group
- C1 of one 3D conformer with its hydrogens, by Athanor’s engine (as in the app)
Elemental analysis
- C29.74%
- H5.82%
- N11.56%
- O26.41%
- S26.47%
Isotope pattern
Each peak is a nominal mass with its abundance-weighted exact mass, as a percentage of the tallest, from IUPAC natural isotope abundances.
Computed from the structure with RDKit 2026.09 when this page was built, beside PubChem's own computed values from its record; where the two differ, both are shown.
Predicted
- log P
- -0.67 Crippen (Wildman and Crippen 1999)
- log S (water solubility)
- -0.04 ESOL (Delaney 2004), log mol/L
- Synthetic accessibility
- 2.98 SA score, 1 easy to 10 hard (Ertl and Schuffenhauer 2009)
Drug-likeness: Lipinski’s rule of five
- Molecular weight ≤ 500: 121.16
- log P ≤ 5 (Crippen): -0.67
- H-bond donors ≤ 5: 3
- H-bond acceptors ≤ 10: 3
Passes all four rules.
¹³C NMR shifts, predicted
Predictions, not measurements; each names its method. A measured log P, where a source reports one, is under Physical properties.
Safety
Warning
Most widely reported: 529 company reports to ECHA. Source [2].
- Harmful or irritant
- H302Harmful if swallowed (55.6% of reports)
- H315Causes skin irritation (11.9% of reports)
- H319Causes serious eye irritation (11.9% of reports)
- H335May cause respiratory irritation (11.9% of reports)
Precautionary statements: P261, P264, P264+P265, P270, P271, P280, P301+P317, P302+P352, P304+P340, P305+P351+P338, P319, P321, P330, P332+P317, P337+P317, P362+P364, P403+P233, P405, P501
View all classifications (2)
- [2] European Chemicals Agency (ECHA)This chemical does not meet GHS hazard criteria for 33.8% (179 of 529) of reports.
- [2] European Chemicals Agency (ECHA) · 529 reports · WarningH302, H315, H319, H335
Storage
- Keep container tightly closed in a dry and well-ventilated place. Store under inert gas. Air sensitive. Storage class (TRGS 510): Non Combustible Solids.[1]
Incompatibilities
- Incompatible materials: Strong oxidizing agents.[1]
Safety data sheets on the supplier’s page: Achemtek, Biosynth, PharmaBlock.
Always read the supplier’s safety data sheet before working with it.
Spectra
- NMRHazardous Substances Data Bank (HSDB) · NMRShiftDB
- 1H NMRHuman Metabolome Database (HMDB) (Varian · 500 MHz · Water) · Human Metabolome Database (HMDB) (Bruker · D2O) · SpectraBase
- 13C NMRHuman Metabolome Database (HMDB) (Bruker · 125 MHz · Water) · Human Metabolome Database (HMDB) (400 MHz · H2O) · SpectraBase
- 1H-1H NMRHuman Metabolome Database (HMDB)
- 1H-13C NMRHuman Metabolome Database (HMDB) (Bruker · 600 MHz · Water)
- GC-MSHuman Metabolome Database (HMDB) (EI-B · positive) · Human Metabolome Database (HMDB) (GC-EI-TOF · positive) · Human Metabolome Database (HMDB) (GC-EI-TOF · positive) · Human Metabolome Database (HMDB) (GC-EI-TOF · positive) · Human Metabolome Database (HMDB) (GC-EI-TOF · positive) · Human Metabolome Database (HMDB) (GC-EI-QQ · positive)
- MS-MSHuman Metabolome Database (HMDB) (QqQ · negative) · Human Metabolome Database (HMDB) (Positive) · Human Metabolome Database (HMDB) (Positive) · Human Metabolome Database (HMDB) (Positive) · Human Metabolome Database (HMDB) (Positive) · Human Metabolome Database (HMDB) (Positive)
- LC-MSMassBank Europe (maXis plus UHR-ToF-MS, Bruker Daltonics · LC-ESI-QTOF · POSITIVE) · MassBank Europe (maXis plus UHR-ToF-MS, Bruker Daltonics · LC-ESI-QTOF · POSITIVE) · MassBank Europe (maXis plus UHR-ToF-MS, Bruker Daltonics · LC-ESI-QTOF · POSITIVE) · MassBank Europe (Agilent 6530 Q-TOF LC/MS · LC-ESI-QTOF · NEGATIVE) · MassBank Europe (LTQ Orbitrap XL, Thermo Scientfic · LC-ESI-ITFT · POSITIVE) · MassBank Europe (LTQ Orbitrap XL, Thermo Scientfic · LC-ESI-ITFT · POSITIVE)
- Other MSHazardous Substances Data Bank (HSDB) · MassBank Europe (GCMS-2010 Plus, Shimadzu · EI-B · POSITIVE) · MassBank Europe (CE-system connected to 6210 Time-of-Flight MS, Agilent · CE-ESI-TOF · POSITIVE) · MassBank of North America (MoNA) (CE-system connected to 6210 Time-of-Flight MS, Agilent · CE-ESI-TOF · ESI) · MassBank of North America (MoNA) (Agilent 6550 iFunnel · Q-TOF · ESI) · MassBank of North America (MoNA) (Agilent 6550 iFunnel · Q-TOF · ESI)
- UVHazardous Substances Data Bank (HSDB)
- IRHazardous Substances Data Bank (HSDB)
- FTIRSpectraBase (KBr WAFER)
- ATR-IRSpectraBase (Bio-Rad FTS · ATR-Neat (DuraSamplIR II))
- RamanSpectraBase (Bruker MultiRAM Stand Alone FT-Raman Spectrometer)
Experimental spectra held by these sources; each link opens the source's own record.
Literature
Reading PubChem, OpenAlex and GSRS…
Bioactivity
Reading ChEMBL…
References
- [1]Hazardous Substances Data Bank (HSDB) · Public domain (US NLM) · via PubChem · retrieved 2026-10-14
- [2]European Chemicals Agency (ECHA) · ECHA legal notice: reuse with acknowledgement · via PubChem · retrieved 2026-10-14
- [3]NMRShiftDB · Linked only · via PubChem · retrieved 2026-10-14
- [4]Human Metabolome Database (HMDB) · Linked only · via PubChem · retrieved 2026-10-14
- [5]SpectraBase · Linked only · via PubChem · retrieved 2026-10-14
- [6]MassBank Europe · Linked only · via PubChem · retrieved 2026-10-14
- [7]MassBank of North America (MoNA) · CC BY 4.0 · via PubChem · retrieved 2026-10-14
- [8]NIST Mass Spectrometry Data Center · Linked only · via PubChem · retrieved 2026-10-14
- ·Calculated values: computed by Athanor with RDKit 2026.09 from the structure.
- ·Literature on PubChem
Data last updated 2026-10-14.