Uric acid

Uric acid

Crystals of urate in polarized light
Names
Systematic IUPAC name 7,9-Dihydro-1H-purine-2,6,8(3H)-trione
Other names 2,6,8-Trioxypurine; 2,6,8-Trihydroxypurine; 2,6,8-Trioxopurine; 1H-Purine-2,6,8-triol
Identifiers
CAS Number	69-93-2 Y
3D model (Jmol)	Interactive image Interactive image
3DMet	B00094
Beilstein Reference	156158
ChEBI	CHEBI:27226 N
ChEMBL	ChEMBL792 Y
ChemSpider	1142 Y
DrugBank	DB01696 Y
ECHA InfoCard	100.000.655
EC Number	200-720-7
IUPHAR/BPS	4731
KEGG	C00366 N
MeSH	Uric+Acid
PubChem	1175
UNII	268B43MJ25 Y
InChI InChI=1S/C5H4N4O3/c10-3-1-2(7-4(11)6-1)8-5(12)9-3/h5,12H,(H,9,10)(H,7,8,11) N Key: DZGSAURIFGGOJK-UHFFFAOYSA-N N InChI=1/C5H4N4O3/c10-3-1-2(7-4(11)6-1)8-5(12)9-3/h(H4,6,7,8,9,10,11,12)/f/h6-9H Key: LEHOTFFKMJEONL-UHFFFAOYAN
SMILES OC1Nc2nc(=O)nc2C(=O)N1 OC1NC2=NC(=O)N=C2C(=O)N1
Properties
Chemical formula	C5H4N4O3
Molar mass	168.11 g·mol−1
Appearance	White crystals
Melting point	300 °C (572 °F; 573 K)
Solubility in water	0.6 mg/100 mL (at 20 °C)
log P	−1.107
Acidity (pKa)	5.6
Basicity (pKb)	8.4
Magnetic susceptibility (χ)	-66.2·10−6 cm3/mol
Thermochemistry
Specific heat capacity (C)	166.15 J K−1 mol−1 (at 24.0 °C)
Std molar entropy (So298)	173.2 J K−1 mol−1
Std enthalpy of formation (ΔfHo298)	−619.69 – −617.93 kJ mol−1
Std enthalpy of combustion (ΔcHo298)	−1921.2 – −1919.56 kJ mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YN ?)
Infobox references

Uric acid is a heterocyclic compound of carbon, nitrogen, oxygen, and hydrogen with the formula C₅H₄N₄O₃. It forms ions and salts known as urates and acid urates, such as ammonium acid urate. Uric acid is a product of the metabolic breakdown of purine nucleotides, and it is a normal component of urine. High blood concentrations of uric acid can lead to gout and are associated with other medical conditions including diabetes and the formation of ammonium acid urate kidney stones.

Uric acid is a diprotic acid with pK_a1 = 5.4 and pK_a2 = 10.3. Thus in strong alkali at high pH, it forms the dually-charged full urate ion, but at biological pH or in the presence of bicarbonate ions, it forms the singly-charged hydrogen urate or acid urate ion. As its second ionization is so weak, the full urate salts hydrolyze back to hydrogen urate salts at pH values around neutral. It is aromatic because of conjugated pi bonding in both rings.

As a bicyclic, heterocyclic purine derivative, uric acid does not protonate from an oxygen (−OH) as carboxylic acids do. X-ray diffraction studies on the hydrogen urate ion in crystals of ammonium hydrogen urate, formed in vivo as gouty deposits, reveal that the keto oxygen in the 2 position of the purine structure (on the carbon between two nitrogens in the six-membered ring) exists as an OH group while the two flanking nitrogen atoms at the 1 and 3 positions share the ionic charge in the six-membered pi-resonance-stabilized ring.