Theoretical calculations on the tautomerism of uric acid in gas phase and aqueous solution

Computational calculations at B3LYP/6-31++G(d,p) level were employed in the study of the predominant tautomeric forms or uric acid (UA) in gas phase and aqueous solution. The triketo form of UA was identified as the most stable tautomer in both cases, whereas monohydroxy species appear to be of minor importance. Deprotonation studies performed over the most stable tautomeric forms of UA in aqueous solution revealed that the proton loss must occur on a monohydroxy tautomer in order to account for the experimental pK_a1 of UA and lead to the most stable monoanionic tautomer in solution.