Trapping of excess electrons at the microhydrated protonated amino groups in proteins

We present a combined first-principles calculation and molecular dynamics simulation study of an excess electron (EE) in condensed phase of a microhydrated protonated amino group in proteins in this work. The protonated amino group, -NH(3)(+), is modeled by a CH(3)NH(3)(+) and an amount of water molecules are included to form various microhydrated CH(3)NH(3)(+) clusters, and the states and the dynamics of the trapped EE are analyzed. In addition to the localized and delocalized states observed, the N-H/O-H bond cleavage phenomena followed by escape of a H atom are also observed for some hydrated clusters in which the -NH(3)(+) group exposes on the surface of the cluster and directly participates in binding an EE. The state-to-state conversion is controlled by thermal motion of molecules in the clusters, and the cleavage of the N-H or the O-H bond and the H escape are determined by the binding modes of the EE. The H-escape nature could be attributed to the dissociation of the N-H or O-H bond induced by the trapped EE which transfers to their antibonding orbitals. This work provides a microscopical picture of the EE trapping at a microhydrated hydrophilic group in proteins, long-range electron migration, and the H-evolving mechanisms relevant for the lesions or damages of proteins or DNA. This is the first step in considering increasingly larger peptide fragments for further investigation of the detailed lesion/damage or charge migration mechanisms. Further work about this topic is underway.