Excess Electron Localization in Solvated DNA Bases

We present a first-principles molecular dynamics study of an excess electron in condensed phase models of solvated DNA bases. Calculations on increasingly large microsolvated clusters taken from liquid phase simulations show that adiabatic electron affinities increase systematically upon solvation, as for optimized gas-phase geometries. Dynamical simulations after vertical attachment indicate that the excess electron, which is initially found delocalized, localizes around the nucleobases within a 15 fs time scale. This transition requires small rearrangements in the geometry of the bases.

Figure 1

Upper panel: AEA of the four microsolvated nucleobases guanine (red, short-dashed line), cytosine (blue, dot-dashed line), adenine (green, long-dashed line) and thymine (black, solid line), as a function of the number of water molecules. Lower panel: averaged adiabatic electron affinity of microsolvated thymine. The solid (red) line is an exponential fit of the calculated data points (stars). The inset shows a typical cluster containing 15 water molecules.

Figure 2

Time evolution of the total spin density after vertical electron attachment in solvated thymine, depicted at times: (a) 0, (b) 5 fs, (c) 10 fs and (d) 25 fs. The contour value is always $1\times {10}^{-3}e/{\AA }^3$.

Figure 3

Upper panel: Evolution of the Mulliken charge in the four solvated nucleobases (colors and line types as in Fig. 1). Lower panel: Mulliken charge located in the thymine orbitals during one of the MD simulations after vertical attachment of an electron. The inset shows a magnification of the initial behavior, up to 25 fs. The various curves correspond to five independent runs.