Conformations Of Disulfide Bonds Studied By Rotational Spectroscopy And Quantum Chemical Calculation

Disulfide bonds refer to the bonds in the half-fatine residues in peptides and protein molecules.The structures and conformations of disulfide bonds are of great significance for understanding the multi-level structure of proteins.But there are few basic studies.In this thesis,dialkyl disulfide compounds are used as model systems to study the structures and conformations of disulfide bonds.Fourier transform microwave spectroscopy was used to study the rotational spectrum of diethyl disulfide and diisopropyl disulfide.Spectral constants were obtained through spectral analysis.The accurate conformations and molecular structures were obtained through spectral constants combined with quantum chemical theory calculations.The conformational characteristics and structures of dialkyl disulfide were analyzed in detail with the help of quantum chemical theory calculations.The complex of diethyl disulfide and argon was studied in order to get detailed information about the intermolecular Van der Waals interaction.The results were reported below:The first chapter was an introduction.The application of disulfide bonds molecules were briefly introduced firstly.Then related theory of rotational spectroscopy,as well as the spectroscopy research of some small molecules with disulfide bonds were introduced.Finally,the basic content of quantum chemistry theoretical calculations and corresponding theoretical calculations of small molecules with disulfide bonds were introduced.The second chapter was mainly about the conformations and structures of diethyl disulfide.Six stable conformers of GGG,GGG',TGG,G'GT,TGT,G'GG'were obtained by theoretical calculations of diethyl disulfide using the MP2/6-311++G(d,p)method in structural optimization and frequency analysis.Two stable conformers GGG and GGG'were investigated by pulsed jet Fourier transform microwave spectroscopy in the rotational spectrum of diethyl disulfide.The relative population ratio of the two conformers were N_GGG/N_GGG??4:1.The two ¹³C and one ³⁴S isotopes of the GGG conformer and the two ³⁴S isotopes of the GGG'conformer spectrum were measured under natural abundance that leaded to accurate spectral constant data.Finally,according to the experimental rotation constants,the structural information such as bond length,bond angle and dihedral angle of diethyl disulfide molecular skeleton were calculated,and the conformational characteristics of diethyl disulfide were systematically analyzed.In the third chapter,diisopropyl disulfide conformations and structures were studied.We also got six stable conformers G'GG',G'GT,GGG',TGT,GGT,GGG of diisopropyl disulfide through MP2/6-311++G(d,p)method.Three conformers,G'GG',G'GT and GGG'were detected in the pulsed jet Fourier transform microwave spectroscopy in the rotational spectrum of diisopropyll disulfide..Their relative population ratio were close to N_G'GG'/N_G'GT/N_GGG'?5:3:2.The rotational spectrum for¹³C and ³⁴S of G'GG'conformer and two ³⁴S of G'GT conformer spectrum were studied in natural abundance that leaded to accurate spectral constant data.Finally,according to the experimental rotation constants,the structural information such as bond length,bond angle and dihedral angle of diisopropyll disulfide molecular skeleton were calculated,and the conformational characteristics of diisopropyl disulfide were systematically analyzed.The fourth chapter through the quantum chemistry theory calculation system to analyze the conformations and structures characteristics of some small disulfide bonds molecules.MP2/6-311++G(d,p)and B3LYP-D3BJ/6-311++G(d,p)results showed that the most stable conformations of disulfide bonds molecules were gauche conformations.When the two sides of the S-S bond were gradually substituted by methyl,ethyl and isopropyl,the S-S bond length and C-S-S-C dihedral angle would decrease while the S-S-C bond angle would increase.The conformation behavior and structures of disulfide bond molecules of olefin groups and aromatics also have similar characteristics.At the same time,experimental structural parameters showed that when the two sides of the S-S bond were gradually displaced from hydrogen atoms to propylene groups,the S-S bond length decreased and S-S-C bond angle increased,while the C-S-S-C dihedral angle had no obvious regularity.In the fifth chapter,diethyl disulfide-argon complex conformations and structures were also studied in detail.Through using the Fourier transform microwave spectrometer,we measured the rotational spectrum of the most stable diethyl disulfide-argon complex.By using different kinds of theoretical calculation methods to study the conformational behavior of the complex,the results have showen that B2PLYP-D3BJ/6-311++G(d,p)rotational constants were in best agreement with the experimental rotational constants.The distances between Ar and the center of mass of diethyl disulfide,sulfur have been determined to be 4.075(16)and 4.007(16)(?),respectively.Ar and diethyl disulfide constituted Van der Waals force interactions at four positions respectively.The total interaction energy of the titled complex was-7.5k J·mol^-1.Energy decomposition analysis of the total interaction energy have shown that dispersion interaction played a dominant role in the total interaction.The sixth chapter was the conclusion and perspective.