Solvent reorganization energies in A-DNA, B-DNA, and rhodamine 6G-DNA complexes from molecular dynamics simulations with a polarizable force field

We estimate solvent reorganization energies γ_s of electron transfer (ET) in DNA stacks between positively charged guanine (acceptor) and neutral guanine (donor), as well as in rhodamine 6G (R6G)-DNA complexes between R6G (acceptor) and neutral guanine (donor) from molecular dynamics simulations that used a polarizable force field in combination with a polarizable water model. We compare results from the polarizable scheme with those from a common nonpolarizable analogue. We also discuss the influence of charge sets, separate contributions of solute and solvent electronic polarizations, and partial contributions of different molecular groups to changes of γ_s due to electronic polarization. Independent of donor-acceptor distances, solvent reorganization energies of ET processes in DNA duplexes from a polarizable force field are about 30% smaller than the corresponding results from a nonpolarizable force field. The effective optical dielectric constant ẽ_∞ ) 1.5, extracted from pertinent scaling factors, is also independent of the donor-acceptor separation over a wide range of distances, from 3.4 to 50.0 Å. Reorganization energies calculated with the polarizable force field agree satisfactorily with experimental data for DNA duplexes. Comparison of results for A-DNA and B-DNA forms as well as for the conformational alignment of the dye relative to the duplex in R6G-DNA complexes demonstrates that the conformation of a duplex hardly affects γ_s. Among these DNA-related systems, the effective parameter ẽ_∞ is remarkably constant over a broad range of donor-acceptor distances.