Azaguanine: A theoretical study of its tautomerism and protonation in the gas phase and aqueous solution

Citation
Jg. Contreras et St. Madariaga, Azaguanine: A theoretical study of its tautomerism and protonation in the gas phase and aqueous solution, BIOORG CHEM, 26(6), 1998, pp. 345-355
Citations number
31
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Chemistry & Analysis","Organic Chemistry/Polymer Science
Journal title
BIOORGANIC CHEMISTRY
ISSN journal
0045-2068 → ACNP
Volume
26
Issue
6
Year of publication
1998
Pages
345 - 355
Database
ISI
SICI code
0045-2068(199812)26:6<345:AATSOI>2.0.ZU;2-A
Abstract
The tautomerism and protonation of 8-azaguanine (azaG) have been studied by means of ab initio methods, both in the gas phase and in aqueous solution. An elimination procedure to choose the most stable tautomeric forms, based on AM1 and HF/6-31G* energies, has been applied. Tautomers azaG(1,9), azaG (1,7) and azaG(9,15) have been selected and their energies calculated at MP 2/6-311++G**//HF/6-31G* level. Self-consistent reaction field IPCM, based o n polarizable continuum model (PCM), has been applied to study the solvent effects. The stability order in the gas phase is azaG(1,7) = azag(1,9) > az aG(9,15), whereas in solution the order becomes azaG(1;7) > azaG(1,9) > aza G(9,15), the latter being just 0.76 kcaI/mol over azaG(1,7). The calculatio ns of proton affinities allowed to unambiguously determine the preferred si tes of protonation of these species. (C) 1998 Academic Press.