This study involves the intramolecular proton transfer (PT) process on a thymine nucleobase between N3 and O2 atoms. We explore a mechanism for the PT assisted by hexacoordinated divalent metals cations, namely Mg2+ , Zn2+ , and Hg2+ . Our results point out that this reaction corresponds to a two-stage process. The first involves the PT from one of the aqua ligands toward O2. The implications of this stage are the formation of a hydroxo anion bound to the metal center and a positively charged thymine. To proceed to the second stage, a structural change is needed to allow the negatively charged hydroxo ligand to abstract the N3 proton, which represents the final product of the PT reaction. In the presence of the selected hexaaqua cations, the activation barrier is at most 8 kcal/mol. © 2017 Wiley Periodicals, Inc.

Department of Chemical Physics and Optics Faculty of Mathematics and Physics Charles University Ke Karlovu 3 Prague 112 16 Czech Republic

Department of Chemistry University of New Orleans New Orleans Louisiana 70148

Department of Theoretical Chemistry Faculty of Chemistry Jagiellonian University R Ingardena 3 Cracow 30 060 Poland

Laboratorio de Química Teórica Computacional Facultad de Química Pontificia Universidad Católica de Chile Vicuña Mackenna 4860 Casilla 306 Correo 22 Santiago Chile

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