|
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
|
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.
|