<unk>  was first isolated from kidney stones in 1776 by Swedish chemist Carl Wilhelm Scheele. In 1882, the Ukrainian chemist Ivan Horbaczewski first synthesized<unk>  by melting urea with glycine.<unk>  displays lactam–lactim tautomerism (also often described as keto–enol tautomerism). Although the lactim form is expected to possess some degree of aromaticity,<unk>  crystallizes in the lactam form, with computational chemistry also indicating that tautomer to be the most stable.<unk>  is a diprotic acid with pKa1 = 5.4 and pKa2 = 10.3, thus at physiological pH, it predominately exists as the monoionic urate ion. + Tautomers of<unk>  and urate 130px 25px 150px pKa125px 150px Lactam form Lactim form Urate ion Water solubility In general, the water solubility of<unk>  and its alkali metal and alkaline earth salts is rather low. All these salts exhibit greater solubility in hot water than cold, allowing for easy recrystallization. This low solubility is significant for the etiology of gout. The solubility of the acid and its salts in ethanol is very low or negligible. In ethanol/water mixtures, the solubilities are somewhere between the end values for pure ethanol and pure water. : + Solubility of urate salts (grams of water per gram of compound) Compound Cold water Boiling water<unk>  15,000 2,000 Ammonium hydrogen urate — 1,600 Lithium hydrogen urate 370 39 Sodium hydrogen urate 1,175 124 Potassium hydrogen urate 790 75 Magnesium dihydrogen diurate 3,750 160 Calcium dihydrogen diurate 603 276 Disodium urate 77 — Dipotassium urate 44 35 Calcium urate 1,500 1,440 Strontium urate 4,300 1,790 Barium urate 7,900 2,700 The figures given indicate what mass of water is required to dissolve a unit mass of compound indicated. The lower the number the more soluble the substance in the said solvent.
Uric acid
Bile acid
Lumirubin
Bilirubin
Blood protein
Calcium
Lipoprotein
Steatocrit