The gas phase proton affinity of uracil: measuring multiple basic sites and implications for the enzyme mechanism of orotidine 5'-monophosphate decarboxylase.

We have shown for the first time experimentally that the O2 and O4 sites of uracil have different proton affinities, and as implied in previous computational studies, the O4 is more basic and would be energetically preferred in an orotate ribose 5'-monophosphate decarboxylase catalysis mechanism involving proton transfer to oxygen.

The acidity of uracil and uracil analogs in the gas phase: four surprisingly acidic sites and biological implications.

The gas phase acidities of a series of uracil derivatives (1-methyluracil, 3-methyluracil, 6-methyluracil, 5,6-dimethyluracil, and 1,3-dimethyluracil) have been bracketed to provide an understanding of the intrinsic reactivity of uracil. The experiments indicate that in the gas phase, uracil has four sites more acidic than water. Among the uracil analogs, the N1-H sites have deltaH(acid) values of 331-333 kcal mol(-1); the acidity of the N3 sites fall between 347-352 kcal mol(-1).