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

Organic & Biomolecular Chemistry Pub Date: 2010-11-10 DOI: 10.1039/C0OB00292E

Abstract

The structures and relative stabilities of the complexes formed by uracil and its thio- and seleno-derivatives with the Sr2+ cation, in the gas phase, have been analyzed by means of G96LYP density functional theory (DFT) calculations. The attachment of the Sr2+ 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 Sr2+ complexes are the most stable. The enhanced stability of these tautomers is two-fold, on the one hand Sr2+ interacts with two basic sites simultaneously, and on the other hand an aromatization of the six-membered ring takes place upon Sr2+ association. Sr2+ 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 Sr2+ 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 Sr2+, all tautomers are energetically accessible and should all be observed in the gas phase.

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