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Internet Electronic Journal of Molecular Design - IEJMD, ISSN 1538-6414, CODEN IEJMAT
ABSTRACT - Internet Electron. J. Mol. Des. July 2006, Volume 5, Number 7, 416-430

Theoretical Study of Direct and Solvent-Assisted Proton Transfer and Tautomerism in the Ground State of 8-Hydroxyadenine
Mama Nsangou, Zoubeida Dhaouadi, Nejm-Eddine Jaïdane, and Zohra Ben Lakhdar
Internet Electron. J. Mol. Des. 2006, 5, 416-430

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Abstract:
Due to the potential misreading of unusual nucleoside the presence of the modified adenine may be the reason for errors occurring during the replication and transcription processes. So that 8-hydroxyadenine is an interesting subject for theoretical studies. DFT method with the hybrid functional denoted B3LYP have been used throughout this work. In order to take into account the bulk of the solvent we have used the self-consistent isodensity polarized continuum model (SCI-PCM). The energy barrier for proton transfer process is quite high in both electronic states (183.3 kJ/mol), but decreases significantly to 50.2 kJ/mol when one water molecule is used as solvent or 39.6 kJ/mol for two water molecules. The same trend is observed in going from gas phase to aqueous phase. Furthermore, in going from gas phase to aqueous phase, the dipole moments of the enolic, keto and TS complexes increase. Their values go respectively from 2.83 D, 2.35 D and 2.60 D to 3.87 D, 3.11 D and 3.47 D, showing that both water-complexed tautomers become more polar. Consequently, it is clear that the effect of solvent bulk is to favor more polarized structures so that charge separation and the dipole moment are clearly higher. The energy barrier for proton transfer process decreases significantly in addition of one and two water molecules in gas phase, and this behavior is more pronounced in aqueous phase.

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