Electron attachment to Cytosine: The Role of Water

TL;DR

This study uses advanced quantum mechanical/molecular mechanical methods to investigate how water influences electron attachment to cytosine, revealing a doorway mechanism and the importance of bulk water in stabilizing anionic states.

Contribution

It demonstrates the necessity of including bulk water effects in simulations and uncovers the ultrafast electron transfer mechanism in solvated cytosine.

Findings

Bulk water stabilizes cytosine anion via hydrogen bonding.

Electron transfer occurs through a doorway mechanism involving water.

Predicted electron affinity matches experimental data.

Abstract

We present an EOM-CCSD based QM/MM study on the electron attachment process to cytosine, solvated in water. The microhydration studies cannot capture the effect of bulk water environment on the electron attachment process and one need to include large number of water molecules in the calculation to get converged results. The electron attachment in the bulk solvated cytosine happened through a doorway mechanism, where the initial electron is localized on water. The electron subsequently gets transferred to cytosine by mixing of electronic and nuclear degrees of freedom which happens at an ultrafast time scale. The bulk water environment stabilizes the cytosine bound anion by an extensive hydrogen-bonding network and enhances the electron transfer rate by manifold from that observed in the gas phase. The predicted adiabatic electron affinity and electron transfer rate obtained from our QM/MM calculations are consistent with the available experimental results.