Tautomerization, Solvent Effect and Binding Interaction on Vibrational Spectra of Adenine-Ag(+) Complexes on Silver Surfaces: A DFT Study

Abstract

Stable structures and vibrational spectra of adenine and adenine-Ag(+) complexes which might exist on silver surfaces have been investigated by hybrid density functional B3LYP and ab initio MP2 methods. For adenine-Ag(+) complexes, considered as monomeric species, there are two stable structures (i-1H-9H-Ag7 and 7H-Ag3) in the gas phase and four stable structures (9H-Ag1, 9H-Ag3, 9H-Ag7 and 7H-Ag3) in aqueous solution calculated with a solvation model of density (SMD). Analyzing the vibrational spectra of these stable structures in the gas phase and in aqueous solution, we can find that Ag(+) influences the spectra significantly and different tautomers can be distinguished from each other on the basis of characteristic bands of their vibrational spectra. Furthermore, we propose that the dimer of 7H-Ag3 should be the most stable structure in aqueous solution though 7H-Ag3 is not the most stable one in the gas phase. This is supported by the predicted Gibbs free energy of the dimerization process and experimental Raman spectra of the adenine-Ag(+) complex.