Simulational Studies Of Excess Electron Interactions With Amino Acid Aqueous Solutions

Electron transfer, constituting an important material-energy foundation of organism metabolism, is an important as well as common phenomenon in biological processes. Thus, it has been a research highlight in the world to study on biological electron transfer processes. On attachment to protein and DNA structures, electrons can do damage by fragmentation reactions. For instance, electron attachment causes fragmentation of phosphodiester bonds of DNA strand. In peptides electron addition usually causes bond cleavage of the amino group or the peptide bond. In the present work, we employed ab initio molecular dynamics (AIMD) simulations combined with density functional theory (DFT) method calculations on several amino acids aqueous solutions with an injected EE. The primary innovations are as follows.1. Reactivity of Excess Electron with Glycine in Aqueous SolutionStudies on the structure, states, and reactivity of excess electrons (EEs) in biological media are of great significance. Although there is information about EE interactions with dry biological molecules, solution effects are hardly explored. In this work, we present an ab initio molecular dynamics simulation study on the interaction and reactivity of an EE with amino acids in solution. Three representative amino acids are considered:glycine, lysine and aspartic acid. Our simulations reveal two striking results. Firstly, a pre-solvated EE partially localizes on the negatively charged-COO-group of the zwitterionic glycine and the remaining part delocalizes over solvent water molecules, forming an anion-centered quasi-localized structure, due to the relative alignment of the lowest unoccupied molecular orbital energy levels of the potential sites for EE residence in the aqueous solution. Secondly, after a period of anion-centered localization of an EE, the zwitterionic glycine is induced to spontaneously fragment through cleavage of the N-Cα bond, losing ammonia (deamination), and leaving a’CH2-COO-anion radical, in good agreement with experimental observations. Introduction of the lysine and aspartic acid side chains can affect EE localization, with the fragmentation of the backbone part of these amino acids dependent on the properties of the side chain group. These findings provide insights into EE interaction mechanisms with amino acids and low energy EE induced fragmentation of amino acids, peptides, and proteins.2. Excess Electron solvation in Proline Aqueous SolutionSimilarly, we employed ab initio molecular dynamics (AIMD) simulations combined with density functional theory (DFT) method calculations on proline aqueous solutions with an injected EE. Proline was applied with its stable zwitterionic form in aqueous solution. Firstly, the mode of proline binding an EE in the gas phase was confirmed by calculations and the possibility of follow-up N-Ca bond cleavage was discussed. By AIMD simulations of EE added proline aqueous solution we find that initially, the EE exhibits a diffuse distribution over a number of water molecules with a localization trend for a part of the EE towards the-COO-anionic group of proline sometimes, similar to the previous simulations of glycine aqueous solution. Finally, the EE is fully solvated into a stable cavity-shaped form nearby the-COO-group of proline and would not disperse in several picoseconds. Thus, zwitterionic proline enhances the cavity-shaped solvation in aqueous solution, which provides a dynamic insight into the process of EE solvation.