Influence of the sequence dependent ionization potentials of guanines on the luminescence quenching of Ru-labeled oligonucleotides:: A theoretical and experimental study

The luminescence quenching by electron transfer of a nonintercalating [Ru(TAP)(2)DIP](2+) complex, which is covalently linked to different guanine containing oligonucleotide duplexes, is compared to the sequence dependent ionization potentials of guanines as estimated from Hartree-Fock calculations on regular B-DNA by means of Koopmans theorem. From these experimental and theoretical results, it is demonstrated that the ionization potential of the guanines has a major influence on the efficiency of hole injection by the groove binding [Ru(TAP)(2)DIP](2+) complex in a type I photooxidation of DNA. Because the photoelectron transfer between the complex and DNA takes place on a nanosecond time scale, nanosecond molecular dynamics simulations were performed for two of the sequences in order to check for the possible influence of the dynamical fluctuations in the DNA structure on the ionization potential. IP fluctuations up to 0.5 eV were observed on a picosecond time scale along the molecular dynamics trajectories. However, these fluctuations scatter statistically around the value calculated for regular B-DNA and are thus not relevant for the slow photoelectron transfer with a nonintercalating [Ru(TAP)(2)DIP](2+) complex.