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Crystals of urate in polarized light
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Names | |||
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Systematic IUPAC name
7,9-Dihydro-1H-purine-2,6,8(3H)-trione
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Other names
2,6,8-Trioxypurine; 2,6,8-Trihydroxypurine; 2,6,8-Trioxopurine; 1H-Purine-2,6,8-triol
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Identifiers | |||
69-93-2 | |||
3D model (Jmol) |
Interactive image Interactive image |
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3DMet | B00094 | ||
156158 | |||
ChEBI | CHEBI:27226 | ||
ChEMBL | ChEMBL792 | ||
ChemSpider | 1142 | ||
DrugBank | DB01696 | ||
ECHA InfoCard | 100.000.655 | ||
EC Number | 200-720-7 | ||
4731 | |||
KEGG | C00366 | ||
MeSH | Uric+Acid | ||
PubChem | 1175 | ||
UNII | 268B43MJ25 | ||
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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) | |||
Std molar
entropy (S |
173.2 J K−1 mol−1 | ||
Std enthalpy of
formation (ΔfH |
−619.69 – −617.93 kJ mol−1 | ||
Std enthalpy of
combustion (ΔcH |
−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).
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what is ?) | (|||
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.