Theoretical Study Of The Related Properties And Applied Electric Field Modulation Of Peptide Electron Transfers

Electron transfer in proteins or peptides not only plays an important role in life activities such as respiration and photosynthesis,but also is of great significance in the design of bioelectronic devices,such as diodes and sensors based on biological molecules.A large number of theoretical and experimental studies have been on the factors,mechanisms,processes and applications of electron transfer in proteins or peptides,and some achievements have been made.However,how to regulate electron transfer has been continuously explored.In this paper,modulation of excess electron in ?-turn,linear and a-helical oligopeptides from molecular nature and external factors were studied by density functional theory.The main achievements and innovations are as follows:(1)Dynamic modulation of molecular vibration on electron transfer relay properties of ?-turn oligopeptides:The relay stations play a significant role in long-range charge hopping transfer in proteins.In this work,we report a dynamic character of a relay with tunable relaying properties using the density functional theory calculations.Our main finding is that a ?-turn peptide can serve as an effective electron relay in facilitating long-range electron migration and its relay properties such as the lowest occupied molecular orbital(LUMO)energy,vertical electron affinity(VEA)and electron-binding mode of the ?-turn oligopeptide and the singly occupied molecular orbital(SOMO)energy of the corresponding electron adduct are vibration-tunable.Different vibration modes lead to different structural distortions and thus have different effects on the relaying properties and ability of the ?-tum peptide.Besides,such relaying properties also vary in the vibration evolution process,and the electron-binding modes may be tunable.As an important addition to the known static charge relaying properties occurring in various protein structural motifs,this work reports the dynamic electron-relaying characteristics governed by molecular vibrations and provides new insights into the dynamics of long-range charge transfers in proteins.(2)Modulation of applied electric field on excess electron transfers along linear oligopeptides:The applied electric field can effectively tune the electron structure and electron transfer properties of the low-dimensional system,however,modulation of excess electron transfer in peptides controlled by the external electric field(Eex)is not clear at present.In this work,density functional theory was used to study electron transfer behavior controlled by Eex in linear oligopeptides and we found that the Eex has modulation on the structure,electronic properties and transfer behavior of electrons in linear oligopeptides.On the one hand,electron-binding ability and dipole moment of linear oligopeptides are sensitive to Eex and can be largely modulated by Ee,due to the competition of Eex and the inner electric field and electron transfer caused by Eex.In the case of low Eex,two structural properties decrease slightly,while for high Eex,the electron-binding ability continually increases strongly,with dipole moments firstly increasing significantly and then increasing more slowly at higher Eex.Additionally,the longer peptide chain length is,the more sensitive modulation of Ee,is.On the other hand,electronic properties represented by electron spin densities and singly occupied molecular orbital distributions vary with Ee,intensities,leading to an unusual electron migration behavior.As Ee.increases,an excess electron transfers from N-terminus to C-terminus,and jumps over a neighboring dipole unit of two termini to other units,respectively,instead of transferring by means of a one-by-one dipole unit hopping mechanism.These findings not only promote a deeper understanding of the connection between Eex and structural and electronic properties of electron transfer behavior in peptides,but also provide a new insight into the modulation of electron migration dynamic along the oligopeptides.(3)Modulation of applied electric field on excess electrons along a-helices oligopeptides:Although many experimental and theoretical studies have reported electron transfer in a-helical peptides,further research is needed on how to tune electron transfer in peptides.In this work,taking a-helical oligopeptides as models,the variations of structure and electron properties of peptides,excess electron distribution and transfer behavior governed by the Ee,which is against the inner dipole electric field were investigated by density functional theory.It was found that the Eex of different intensities can modulate the electron binding abilities,dipole moments,electron distributions and electron transfer behavior of ?-helical oligopeptides.In low Eex,the binding electron abilities of ?-helical oligopeptides decrease,and the dipole moments change slightly.In high Eex,the electron binding abilities increase greatly,and the dipole moments increase significantly and then increase gentlely in higher Eex.As Eex increases,an excess electron jumps from the N-terminus of the peptides to the C-terminus.In addition,?-helical oligopeptides with different chain lengths have different sensitivity to Eex.The longer the chain length is,the more obvious the effects of the Eex on the binding electron ability and dipole moment of the peptides are,the larger the modulation range is,the lower the Eex required by the ?-helical oligopeptides to complete the electron transfer is,and the faster the electron transfer is.This work further enriches the information about the electron transfer of ?-helical peptides and provides an idea on how to modulate the charge transfer of peptides.