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Issue 20, 2008
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Interaction of Ca2+ with uracil and its thio derivatives in the gas phase

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The structures and relative stabilities of the complexes formed by uracil and its sulfur derivatives, namely, 2-thio-, 4-thio, and 2,4-dithio-uracil when interacting with Ca2+ in the gas phase have been analyzed by means of density functional theory (DFT) calculations carried out at the B3LYP/6-311++G(3df,2p)//B3LYP/6-31+G(d,p) level. For uracil and 2,4-dithiouracil, where the two basic sites are the same, Ca2+ attachment to the heteroatom at position 4 is preferred. However, for the systems where both types of basic centers, a carbonyl or a thiocarbonyl group, are present, Ca2+–oxygen association is favored. The most stable complexes correspond to structures with Ca2+ bridging between the heteroatom at position 2 of the 4-enol (or the 4-enethiol) tautomer and the dehydrogenated ring nitrogen, N3. The enhanced stability of these enolic forms is two-fold, on the one hand Ca2+ interacts with two basic sites and on the other triggers a significant aromatization of the ring. Besides, Ca2+ association has a clear catalytic effect on the tautomerization processes which connect the oxo–thione forms with the enol–enethiol tautomers. Hence, although the enol–enethiol tautomers of uracil and its thio derivatives should not be observed in the gas phase, the corresponding Ca2+ complexes are the most stable species and should be accessible, because the tautomerization barriers are smaller than the Ca2+ binding energies.

Graphical abstract: Interaction of Ca2+ with uracil and its thio derivatives in the gas phase

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Publication details

The article was received on 19 Jun 2008, accepted on 11 Jul 2008 and first published on 08 Aug 2008

Article type: Paper
DOI: 10.1039/B810418B
Citation: Org. Biomol. Chem., 2008,6, 3695-3702
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    Interaction of Ca2+ with uracil and its thio derivatives in the gas phase

    C. Trujillo, A. M. Lamsabhi, O. Mó, M. Yáñez and J. Salpin, Org. Biomol. Chem., 2008, 6, 3695
    DOI: 10.1039/B810418B

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