Arginine is the amino acid with the formula (H₂N)(HN)CN(H)(CH₂)₃CH(NH₂)CO₂H. The molecule features a guanidino group appended to a standard amino acid framework. At physiological pH, the carboxylic acid is deprotonated (−CO₂⁻) and both the amino and guanidino groups are protonated, resulting in a cation. Only the l-arginine (symbol Arg or R) enantiomer is found naturally. Arg residues are common components of proteins. It is encoded by the codons CGU, CGC, CGA, CGG, AGA, and AGG. The guanidine group in arginine is the precursor for the biosynthesis of nitric oxide. Like all amino acids, it is a white, water-soluble solid.

Arginine

Skeletal formula of arginine
Ball-and-stick model Space-filling model
Names
IUPAC names Arginine
Other names 2-Amino-5-guanidinopentanoic acid
Identifiers
CAS Number	L: 74-79-3 Y D/L: 7200-25-1 Y D: 157-06-2 Y L HCl: 1119-34-2 Y
3D model (JSmol)	L: Interactive image D: Interactive image L HCl: Interactive image L Zwitterion: Interactive image
3DMet	L: B01331
Beilstein Reference	1725411, 1725412 D, 1725413 L
ChEBI	L: CHEBI:29016 Y
ChEMBL	L: ChEMBL1485 Y D: ChEMBL212301 Y
ChemSpider	L: 6082 Y D/L: 227 Y D: 64224 Y
DrugBank	L: DB00125 Y
ECHA InfoCard	100.000.738
EC Number	L: 230-571-3
Gmelin Reference	364938 D
IUPHAR/BPS	L: 721
KEGG	L: C02385 Y
MeSH	Arginine
PubChem CID	L: 6322 D/L: 232 D: 71070
RTECS number	L: CF1934200 L
UNII	L: 94ZLA3W45F Y D/L: FL26NTK3EP Y D: R54Z304Z7C Y L HCl: F7LTH1E20Y Y
CompTox Dashboard (EPA)	L: DTXSID6041056
InChI InChI=1S/C6H14N4O2/c7-4(5(11)12)2-1-3-10-6(8)9/h4H,1-3,7H2,(H,11,12)(H4,8,9,10)/t4-/m0/s1 Y Key: ODKSFYDXXFIFQN-BYPYZUCNSA-N Y D/L: Key: ODKSFYDXXFIFQN-UHFFFAOYSA-N D: Key: ODKSFYDXXFIFQN-SCSAIBSYSA-N
SMILES L: C(C[C@@H](C(=O)O)N)CNC(=N)N D/L: C(CC(C(=O)O)N)CNC(=N)N D: C(C[C@H](C(=O)O)N)CNC(=N)N L HCl: [Cl-].NC(CCCNC(N)=[NH2+])C([O-])=O L Zwitterion: NC(CCCNC(N)=[NH2+])C([O-])=O
Properties
Chemical formula	C6H14N4O2
Molar mass	174.204 g·mol−1
Appearance	White crystals
Odor	Odourless
Melting point	260 °C; 500 °F; 533 K
Boiling point	368 °C (694 °F; 641 K)
Solubility in water	14.87 g/100 mL (20 °C)
Solubility	slightly soluble in ethanol insoluble in ethyl ether
log P	−1.652
Acidity (pKa)	2.18 (carboxyl), 9.09 (amino), 13.8 (guanidino)
Thermochemistry
Heat capacity (C)	232.8 J K−1 mol−1 (at 23.7 °C)
Std molar entropy (S⦵298)	250.6 J K−1 mol−1
Std enthalpy of formation (ΔfH⦵298)	−624.9–−622.3 kJ mol−1
Std enthalpy of combustion (ΔcH⦵298)	−3.7396–−3.7370 MJ mol−1
Pharmacology
ATC code	B05XB01 (WHO) S
Hazards
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H319
Precautionary statements	P305+P351+P338
Lethal dose or concentration (LD, LC):
LD50 (median dose)	5110 mg/kg (rat, oral)
Safety data sheet (SDS)	L-Arginine
Related compounds
Related alkanoic acids	N-Methyl-D-aspartic acid beta-Methylamino-L-alanine Guanidinopropionic acid Theanine Pantothenic acid
Related compounds	Panthenol
Supplementary data page
Arginine (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references