Hydrogen-bonded proton transfer in the hydrated adenine-thymine anion

The proton transfer processes of microhydrated adenine-thymine anions are studied using density functional theory with the B3LYP method and DZP++ basis set. The microhydration effects on the geometrical structures, adsorption site, and the proton transfer reaction of the adenine-thymine anion are investigated. The site N-10 atom of the adenine moiety has a larger proton affinity than the site O-24 atom of thymine, which facilitates the proton H-26 transfers from the N-25 site of thymine to the N-10 site of adenine. Therefore, the first single-proton transfer pathway (SPT1) is found for the all of the monohydrated adeninethymine anions (AN(4)T)(-)center dot H2O, (AN(13)T)(-)center dot H2O, (AT(O24))(-)center dot H2O, and (ATO(28))(-)center dot H2O and tetrahydrated adenine-thymine anions (AT)(-)center dot 4H(2)O. The proton H-9 at the N-7 site of adenine is also found to transfer to the O-24 site of thymine for (AN(4)T)(-)center dot H2O and (AN(13)T)(-)center dot H2(O) in the gas phase. The double-proton transferred pathway is found when one water molecule interacts with the O-28 atom of thymine. The reactant structures before the proton transfer are more stable than the product structures, and the structural changes mainly occur in thymine. The reaction energies of the microhydrated adenine-thymine anion in the gas phase and in the aqueous environment predict that the proton transfer process of the microhydrated adenine-thymine anion are more favorable in the gas phase than in aqueous solution.