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Uric acid

Uric acid
Harnsäure Ketoform.svg
Uric acid3D.png
Fluorescent uric acid.JPG
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
69-93-2 YesY
3D model (Jmol) Interactive image
Interactive image
3DMet B00094
156158
ChEBI CHEBI:27226 N
ChEMBL ChEMBL792 YesY
ChemSpider 1142 YesY
DrugBank DB01696 YesY
ECHA InfoCard 100.000.655
EC Number 200-720-7
4731
KEGG C00366 N
MeSH Uric+Acid
PubChem 1175
UNII 268B43MJ25 YesY
Properties
C5H4N4O3
Molar mass 168.11 g·mol−1
Appearance White crystals
Melting point 300 °C (572 °F; 573 K)
0.6 mg/100 mL (at 20 °C)
log P −1.107
Acidity (pKa) 5.6
Basicity (pKb) 8.4
-66.2·10−6 cm3/mol
Thermochemistry
166.15 J K−1 mol−1 (at 24.0 °C)
173.2 J K−1 mol−1
−619.69 – −617.93 kJ mol−1
−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 YesYN ?)
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 pKa1 = 5.4 and pKa2 = 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.


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