Interactions of Solvated Electrons with Nucleobases: The Effect of Base Pairing

Abstract

We have investigated the effect of base pairing on the electron attachment to nucleobases in bulk water, taking the guanineÀ cytosine (GC) base pair as a test case. The presence of the complementary base reinforces the stabilization effect provided by water and preferentially stabilizes the anion by hydrogen bonding. The electron attachment in bulk-solvated GC happens through a doorway mechanism, where the initial electron attached state is water bound, and it subsequently gets converted to a GC bound state. The additional electron in the final GC bound state is localized on the cytosine, similar to that in the gas phase. The transfer of the electron from the initial water-bound state to the final GC bound state happens due to the mixing of electronic and nuclear degrees of freedom and takes place at a picosecond time scale.[a] Dr.

Electron Attachment to Cytosine: The Role of Water

“…The calculated rate is 5-fold larger from that observed for microsolvated states which highlight the crucial role played by the bulk water in electron attachment process. The rate of electron transfer from the initial water localized state to the final nucleobase localized state in bulk solvated cytosine is almost half of that observed for cytosine in bulk solvated GC base pair 57 . This indicates the cooperativity effect of base-pairing with the solvation in the electron attachment process.…”

“…The rates are much slower than those observed for microhydrated uracil 57 or microhydrated GC base pair. 58 However, microsolvation leads to at least a four-fold increase in the rate of transition from the gas-phase value of 1.6 × 10 5 s −1 . It shows that the presence of even one water molecule can increase the stability of the valence-bound state and consequently increases the rate of transfer of an electron from the dipole-bound to the valence-bound state, which is consistent with previously reported results.…”

Doorway Mechanism for Electron Attachment Induced DNA Strand Breaks

“…Earlier work of Sommerfeld and our previous works ,− have shown the dipole-bound states as an efficient doorway for the capture of electrons in DNA bases. The picture becomes more complex in the presence of an aqueous solvent.…”

“…We have recently shown that the doorway mechanism is a generalized path to the formation of stable nucleobase anion, 34 and this even exists in the condensed phase, where solvent-bound states act as a doorway state. [35][36][37] This raises the possibility of a doorway mechanism for LEE-induced DEA process in genetic materials. Previous studies have shown that purine nucleobases have the highest VEA among the nucleobases.…”

“…The formation of valence π*-type anion reduces the possibility of electron transfer to the dissociative C–O/C–N σ* state. Moreover, the stability of the valence π*-type anion has been known to increase drastically in the aqueous phase, , which will enhance the rate of formation of stable π*-type valence-bound anionic state in the solvent phase. Our initial studies with monohydrated cytosine nucleotide have shown (see Supporting Information) that even the presence of one water molecule can increase the rate of valence π*-type anion formation and decrease the rate of formation of dissociative valence C–O σ* state.…”