Theoretical studies on the single proton transfer process in adenine base

The effect of metal ions (Mⁿ⁺ = Na⁺, K⁺, Mg²⁺, Ca²⁺, Zn²⁺ and hydrated Mg²⁺ ions) and water molecules on the tautomerism of adenine induced by single intramolecular proton transfer (SPT) have been investigated theoretically. Calculated results show that the single proton transfer process in adenine base is favored and even becomes thermodynamically spontaneous because of the presence of Mⁿ⁺ interacting at the N₃ position of adenine. On the contrary, if Mⁿ⁺ coordinated to N₇ site, the single proton transfer process will become unfavorable than that in the neutral system. The effects of metal ions on the SPT of adenine base are more pronounced if Lewis acidity of metal ion is increased. Water plays a more important role than metal ions during the SPT process. It is found that water can act not only as a solvent but also as a mediator which gives and accepts protons to promote SPT, playing a bridge role. As a result, inclusion of a water molecule drastically reduces the energy barrier for the SPT. Moreover, two water molecules can yield larger assisting effect on the SPTs compared with one water molecule. We can conclude that the tautomerism of DNA adenine base can be modulated by the metal ions and water molecules. Copyright © 2015 John Wiley & Sons, Ltd.