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Issue 19, 2007
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A theoretical study of hydration effects on the prototropic tautomerism of selenouracils

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Abstract

The prototropic tautomerism of 2-, 4-selenouracil and 2,4-diselenouracil has been studied using density functional theory (DFT) methods, at the B3LYP/6–311 + G(3df,2p)//B3LYP/6–31G(d,p) level. The relative stability order of selenouracil tautomers does not resemble that of uracil tautomers, but it is similar to that of thiouracils, even though the energy gaps between the different tautomers of selenouracils are smaller than for thiouracils. The tautomerism activation barriers are high enough as to conclude that only the oxo-selenone or the diselenone structures should be found in the gas phase. The specific interaction with one water molecule reduces these barriers by a half, but still the oxo-selenone form is always the most stable tautomer. The addition of a second water molecule has a relatively small effect, as well as bulk effects, evaluated by means of a continuum-polarized model. For isolated 2- and 4-selenouracils, the more favorable tautomerization process corresponds to a hydrogen transfer towards the selenium atom, the activation barriers for transfer towards the oxygen atom being much higher. This situation changes when specific and bulk effects are included, and the latter process becomes the more favorable one. For 2,4-diselenouracil the more favorable tautomerization, in the gas phase, corresponds to the H shift from N1 to the Se atom at C2, while solvation effects favor the transfer from N3 to the Se atom at C4.

Graphical abstract: A theoretical study of hydration effects on the prototropic tautomerism of selenouracils

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Publication details

The article was received on 29 May 2007, accepted on 12 Jul 2007 and first published on 15 Aug 2007


Article type: Paper
DOI: 10.1039/B708045J
Citation: Org. Biomol. Chem., 2007,5, 3092-3099
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    A theoretical study of hydration effects on the prototropic tautomerism of selenouracils

    C. Trujillo, O. Mó and M. Yáñez, Org. Biomol. Chem., 2007, 5, 3092
    DOI: 10.1039/B708045J

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