Transitions to high tautomeric states can be induced in adenine by interactions with carboxylate and sodium ions: DFT calculation data

Twelve triple complexes of nine adenine tautomers with carboxylate ion of acetic acid CH3COOK and sodium ion NaC of the CH3COOK:Ade:NaC type were studied by the B3LYP/6-311CCG(d,p)//B3LYP/6-31G(d,p) quantum chemical method. It was established that three rare adenine tautomers generate more stable complexes than the ground state one. The B3LYP/6-311CCG(d,p) full optimization was applied to four most stable triple complexes in order to refine on their stability order. To evaluate contributions of each ligands for stabilization of these complexes, calculations of energies and dipole moments of respective binary complexes of the CH3COOK:Ade and Ade:NaC types were performed at the B3LYP/6-31CCG(d,p) level of theory. At the same level, there were computed energies and dipole moments of isolated tautomers. Two of them, first calculated in this work, appeared to be zwitter-ions. Highly cooperative interplay of interactions of both ligands with adenine tautomers was observed in triple complexes. Preferable sites of coordination of NaC with tautomers were ascertained. Biological importance of the results obtained is discussed. q 2004 Published by Elsevier B.V.