Excess electron reactivity in amino acid aqueous solution revealed by ab initio molecular dynamics simulation: anion-centered localization and anion-relayed electron transfer dissociation

Abstract

Studies on the structure, states, and reactivity of excess electrons (EEs) in biological media are of great significance. Although there is information about EE interaction with desolvated 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 glycine in solution. 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 relative alignment of the lowest unoccupied molecular orbital energy levels of 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 the 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 same groups (-COO(-) or -NH3(+)) in the side chain (taking lysine and aspartic acid as examples) can affect EE localization, with the fragmentation of the backbone part of these amino acids dependent on the properties of the side chain groups. These findings provide insights into EE interaction mechanisms with the backbone parts of amino acids and low energy EE induced fragmentation of amino acids and even peptides and proteins.

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“…Unfortunately, our approach does not allow determining the reaction barrier. However, a first-principles molecular dynamics (FPMD) study revealed this mode of action as well [ 80 ]. Initially, the electron binds to the carboxyl group of glycine.…”

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“…Several studies involve dynamic cluster models rather than the condensed-phase ones. − Interesting per se , reaction mechanisms in clusters can be different from those in the bulk. In some articles, substrates after electron attachments are simulated both in clusters ,, and in the condensed phase, concentrating on relaxation kinetics but omitting the diffusion and electron transfer. Finally, simple generalized gradient approximation (GGA) DFT , is applied for condensed-phase MD, despite the delocalization error.…”

Solvated electrons in the complex media: a review

“…Figure 18 The representative dielectron clathrate hydrate bi-cavity structure, spin density distribution and the spin coupling pathway of two electrons (a) and the electric field regulated changes of spin denisty and spin coupling contants (b) [76,77] (color online). [63] (网络版彩图) [78] (网络版彩图)…”

“…Figure 20 The simulation of the solvated-electron-induced N−C α bond cleavage process of glycine in the aqueous glycine solution [78] (color online).…”