Molecular Modeling Studies On The Transport Mechanism Of SWEET Protein And The Photoelectric Properties Of Defect Molybdenum Diselenide

Molecular modeing uses computer to simulate molecular structure and behavior at atomic level,and then obtains various physical and chemical properties of molecular system.Molecular modeing can not only simulate many experiments which are difficult or impossible to accomplish in reality,but also is more efficient,economical and safe than ordinary experimental methods.Quantum mechanics simulation and classical mechanics simulation are its two main research directions.In the first part of this paper,the transport mechanism of SWEET protein was studied by classical mechanics simulation method,and a three-state transport model of SWEET protein was proposed.In the second part,the reason of Physicochemical properties change on molybdenum diselenide repaired by halogen was studied by using quantum mechanics simulation method.The reason of photoluminescence enhancement of molybdenum diselenide repaired by halogen was well explained.In the first part,according to the crystal structure of the SWEET protein in rice,we simulated the Inward-open conformation model of the SWEET protein encoded by human gene Q9BRV3 by homology modeling method.This model is helpful for us to have a clear understanding of the human SWEET transporter family.It has reference value for the crystal structure analysis,physiological function understanding,drug targets search and protein structure design of human SWEET protein.Secondly,the OsSWEET2b protein(5CTG)of eukaryote and SemiSWEET proteins(4X5M,4X5N and 4QNC)of prokaryotic were studied by conventional molecular dynamics simulation.C55,N77,F181 and N197 were the key amino acids of 5CTG,and T15,W50 and N66 were the key amino acids of SemiSWEET protein.In addition,only one of the three transport channels in SWEET protein was changed its conformation to transport substrates at the same time,and the other two were in the ready state.After a steered molecular dynamics simulation,we found that N77-N197 and W70-W189 together to maintain the shape of the transport channel N77-N197 can form hydrogen bonds with the substrate molecule to keep the molecule moving forward.W70-W189 forms a gated channel,which controls the entry of the substrate like a door.During the transport process,the upper end of TM1 rotates about 30 degrees,which providing momentum for conformational change.Finally,we propose that SWEET protein transport substrate molecules through a three-state transport model mechanism.In the second part,using first-principles calculations,we have investigated the electronic and optical properties of MoSe2 with Se vacancies(SVse,a-DVse,and ?-DVse)and further repaired by halogen atoms(F,Cl,Br and I).For the MoSe2 with Se vacancies,Cl,Br and I atoms can occupy the original Se vacancies and form three bonds with the neighboring Mo atoms,but F atom only can form two F-Mo bonds with the lowest adsorption energies due to its smaller atomic radius.Halogen atoms possess one more electron than Se atom,which results in a local magnetic moment of 1 ?B for single vacancy and 2 ?B for double vacancies.The Se vacancies induce some defective energy levels in the band structures and make the band gap smaller.After repaired by halogen atoms,the electrons transferring from halogen atoms induce a n-doping in MoSe2,and finally shift the defective energy levels into valance band.Compared to the defective MoSe2,absorption enhancement is observed in the halogen-repaired MoSe2 structures.Our results provide new insights in structure repairing of the transition metal dichalcogenides and promote their remarkable properties for applications in optoelectronics.