Trapping Of Excess Electrons At The Microhydrated Protonated Amino Groups In Proteins

The charge transfer between cofactors in proteins are widespread, such as respiration, metabolism, photosynthesis, nitrogen fixation, gene replication and signal transduction of biology and so on. The investigation of electron transfer attracts many subject’s attention, such as Physics, Chemistry, Biology, and Medicine. It plays a critical role for the electron transfer to solve many biological problems. In long range electron transfer process, the electron temporarily resides on a relay station for a short time during its passage from one redox site to another. Protonated amino group acting as a hydrophilic group may associate with water molecules together to reside the excess electron. We perform a series of work and obtain many valuable results on these issues. The primary information are as follows:1. The Simulation investigation:Trapping of excess electrons at the microhydrated protonated amino groupsIn this work, we present a combined quantum chemical calculation and ab initio molecular dynamics simulation study of an excess electron in condensed phase of a microhydrated protonated side-chain amino group of lysine residue in proteins. The protonated side-chain amino group,-NH3+, is modeled by a CH3NH3+and an amount of water molecules are included to form various microhydrated CH3NH3+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 bond cleavage phenomena followed by escape of H atom are also observed for some hydrated clusters in which the-NH3+group exposes on the surface of the cluster and directly participate in binding the EE. The state-to-state conversion is controlled by thermal motion of molecules in the clusters and the cleavages of the N-H and the H-escape are determined by the binding modes of the excess electron. The H-escape nature could be attributed to the cleavage of the N-H bonds induced by excess electron transferring to their antibonding σ*orbital. This work provides a picture of the EE trapping at a micro-hydrated hydrophilic group in proteins, long-range electron migration, and the H-evolving mechanisms.2. Stable ability investigation:Trapping of excess electrons at the microhydrated protonated amino groupsIn this work, we choose different solvated protonated methylamine clusters to study. On the one hand, we study the excess electron state in different clusters; on the other hand, we study the bond ability variation of the N-H/O-H bond, when the excess electron is captured by the dangling H of the-NH3+terminal and the water molecules. We find that when the EE is captured by a little cluster, the EE bound motifs can be distinguished:(1) Rydberg state (2) surface state (3) cavity state. The Rydberg state EE is not stable. It is easy for the EE to transfer to the N-H σ*antibonding orbital giving rise to the N-H bond cleavage and the H radical formation. The surface state EE is usually found by us in little clusters. It is also easy for the EE to localize in the N-H a*antibonding orbital giving rise to the N-H bond cleavage. But for the cavity state EE, it is stable enough to localize in the cavity formed by the dangling H of-NH3+terminal and water molecules, which is difficult in localizing in the N-H a*antibonding orbital. Thus, the cavity state electron is not easy to give rise to N-H bond cleavage. When the protonated methylamine cluster may provide the EE with the lower O-H bond energy orbital, and the EE is mainly captured by the dangling H of water molecules, which give rise to the O-H bond cleavage. The O-H bond cleavage can be explained by a nonsynergistic double proton transfer mechanism. The EE occupies the antibonding σ*orbital of O-H, causing the O-H bond to rupture. Then, the proton of the-NH3+-terminal attacks the O atom, causing the new water molecule formation.