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Org Biomol Chem. 2011 Jan 21;9(2):423-31. doi: 10.1039/c0ob00292e. Epub 2010 Nov 10.

Effect of Sr2+ association on the tautomerization processes of uracil and its dithio- and diseleno-derivatives.

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Departamento de Química, Módulo 13, Universidad Autónoma de Madrid, Cantoblanco, Campus de Excelencia UAM-CSIC, 28049-Madrid, Spain.


The structures and relative stabilities of the complexes formed by uracil and its thio- and seleno-derivatives with the Sr(2+) cation, in the gas phase, have been analyzed by means of G96LYP density functional theory (DFT) calculations. The attachment of the Sr(2+) cation to the heteroatom at position 4 is preferred systematically. Although the enolic forms of uracil and its derivatives should not be observed in the gas phase, the corresponding Sr(2+) complexes are the most stable. The enhanced stability of these tautomers is two-fold, on the one hand Sr(2+) interacts with two basic sites simultaneously, and on the other hand an aromatization of the six-membered ring takes place upon Sr(2+) association. Sr(2+) attachment also has a clear catalytic effect in the tautomerization processes involving uracil and its derivatives. This catalytic effect increases when oxygen is replaced by sulfur or selenium. The Sr(2+) binding energy with uracil and its derivatives is bigger than the tautomerization barriers connecting the dioxo forms with the corresponding enolic tautomers. Consequently, when associated with Sr(2+), all tautomers are energetically accessible and should all be observed in the gas phase.

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