Studies On Electron Relay Stations Of Long-range Electron Transfer In Proteins

Electron transfer(ET) in proteins plays a vital role in many biochemical processes. To understand the exact pathway of ET in proteins for these biological processes, extensive investigations in experiment and theory have been carried out in recent decades. Nowadays, there are two mechanisms to explain the ET in proteins: one-step superexchange mechanism and multistep hopping mechanism. In the superexchange mechanism, electron directly transfers form the donor to the close accepter at one step. In the hopping mechanism, there are one or more relay stations which can transiently carry electron or hole, the charge will transfer between donor and accepter via several steps.The long-range ET reactions in proteins are common in many biological activities, which mechanism are of much interests. Meanwhile, the relay stations between donor and accepter play an important role in the long-range ET processes in proteins. Three types of relay stations for ET in proteins are examined in this thesis. These findings may provide a further understanding of ET pathway in proteins.(1)S:?\S???S\?:S three-body five-electron relay station. A type of relay station for electron transfer in proteins, three-piece five-electron bonding, is introduced in this part, which is also first proposed here. The ab inito calculations predict the formation of S:?\S???S\?:S resonance binding with an aromatic ring located in the middle of two sulfur-containing groups, which may participate in electron-hole transport in proteins. These special structures can lower the local ionization energies to capture electron holes efficiently and may be easily formed and broken because of their proper binding energies. In addition, the UV-vis spectra provide evidence of the formations of the three-piece five-electron binding. The cooperation of three adjacent pieces may be advantage to promote electron transfer a longer distance.(2)?:S\?????\S:? and ?:?\S????\?:S three-body five-electron relay stations. The cooperative interactions among two aromatic rings with a S-containing group are described, which may participate in electron hole transport in proteins. Ab inito calculations reveal the possibility for the formations of the ?:S\?????\S:? and ?:?\S????\?:S five-electron bindings in the corresponding microsurrounding structures in proteins, both facilitating electron hole transport as efficient relay stations. The relay functionality of these two special structures comes from their low local ionization energies and proper binding energies, which varies with the different aromatic amino acids, S-containing residues, and the arrangements of the same aromatic rings according to the local micro surroundings in proteins.(3)?:?\?????\?:? three-body five-electron relay station. Aromatic amino acid plays important role in many ET processes in proteins, according to previous research, single aromatic amino acid and two aromatic amino acids structure can act as electron relay station in long-range ET in proteins. The possibility of tri- or more aromatic-ring system acting as relay station is discussed in this part. The calculations predict the formation of ?:?\?????\?:? binding interaction when three side chains of aromatic amino acid located in the proper location. When the three-body system captures an electron hole, the MOs of three aromatic rings generate three HOMOs which can form the five-electron interaction. The formation of this three-? five-electron binding can lower the local IEv and the BEs are proper to support the formations and separations of the special bondings.