Histamine

Histamine

Names
IUPAC name 2-(1H-Imidazol-4-yl)ethanamine
Identifiers
CAS Number	51-45-6 Y
3D model (Jmol)	Interactive image
ChEBI	CHEBI:18295 Y
ChEMBL	ChEMBL90 Y
ChemSpider	753 Y
ECHA InfoCard	100.000.092
IUPHAR/BPS	1204
KEGG	D08040 Y
MeSH	Histamine
PubChem	774
UNII	820484N8I3 Y
InChI InChI=1S/C5H9N3/c6-2-1-5-3-7-4-8-5/h3-4H,1-2,6H2,(H,7,8) Y Key: NTYJJOPFIAHURM-UHFFFAOYSA-N Y InChI=1/C5H9N3/c6-2-1-5-3-7-4-8-5/h3-4H,1-2,6H2,(H,7,8) Key: NTYJJOPFIAHURM-UHFFFAOYAP
SMILES NCCC1=C[N]C=N1
Properties
Chemical formula	C5H9N3
Molar mass	111.15 g·mol−1
Melting point	83.5 °C (182.3 °F; 356.6 K)
Boiling point	209.5 °C (409.1 °F; 482.6 K)
Solubility in water	Easily soluble in cold water, hot water
Solubility in other solvents	Easily soluble in methanol. Very slightly soluble in diethyl ether. Easily soluble in ethanol.
log P	−0.7
Acidity (pKa)	Imidazole: 6.04 Terminal NH2: 9.75
Pharmacology
ATC code	L03AX14 (WHO) V04CG03 (WHO) (phosphate)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y  (what is YN ?)
Infobox references

Histamine is an organic nitrogenous compound involved in local immune responses as well as regulating physiological function in the gut and acting as a neurotransmitter. Histamine is involved in the inflammatory response and has a central role as a mediator of pruritus. As part of an immune response to foreign pathogens, histamine is produced by basophils and by mast cells found in nearby connective tissues. Histamine increases the permeability of the capillaries to white blood cells and some proteins, to allow them to engage pathogens in the infected tissues.

Histamine base, obtained as a mineral oil mull, melts at 83–84 °C. Hydrochloride and phosphorus salts form white hygroscopic crystals and are easily dissolved in water or ethanol, but not in ether. In aqueous solution, histamine exists in two tautomeric forms: N^π-H-histamine and N^τ-H-histamine. The imidazole ring has two nitrogens. The nitrogen farthest away from the side chain is the 'tele' nitrogen and is denoted by a lowercase tau sign. The nitrogen closest to the side chain is the 'pros' nitrogen and is denoted by the pi sign. The position of the nitrogen with the hydrogen on it determines how the tautomer is named. If the nitrogen with the hydrogen is in the tele position, then histamine is in the tele-tautomer form. The tele-tautomer is preferred in solution.

Histamine has two basic centres, namely the aliphatic amino group and whichever nitrogen atom of the imidazole ring does not already have a proton. Under physiological conditions, the aliphatic amino group (having a pK_a around 9.4) will be protonated, whereas the second nitrogen of the imidazole ring (pK_a ≈ 5.8) will not be protonated. Thus, histamine is normally protonated to a singly charged cation.