Unexpectedly Small Effect of the DNA Environment on Vertical Ionization Energies of Aqueous Nucleobases

By a combination of ab initio calculations and photoelectron spectroscopy, we demonstrate that the DNA surrounding has only a negligible effect on ionization energies of nucleobases in the native aqueous environment. The aqueous solution thus effectively screens the sugar–phosphate backbone and the neighboring nucleobases. Consequently, vertical ionization potentials of nucleobases in aqueous DNA can be reliably derived from the corresponding values for its building blocks in water, that is, aqueous nucleobases, nucleosides, or nucleotides.