Theoretical Study On The Vibrational Spectroscopy Of Several Ginsenoside Molecules And Chlorophenol Derivatives

Vibrational spectroscopy is an important method to investigate molecular structure, intra- and inter-molecular interaction.The peaks positions,intensity and shape of spectra have close relation with the chemical structure,spatial geometry,molecular force field and distribution of electron cloud and so on.It is well-known that assigning and analyzing vibration spectrum is the basis of studying molecular structure.The different substance possesses different characteristic spectrum,then one can investigate the relation between molecular structure and character of spectrum.Now, the theory of molecular vibration frequency makes a great progress and gets satisfactory results,which can be as effective contrast for the attribution of experimental frequency.Thus we have theoretically studied and simulated the vibration spectrums combining with experiment results to assigne and analyze the infrared spectrum and Raman one.In this thesis,the molecular structure character and spectral information of a series of Chinese medicine molecules and several substituted chloro-phenols ones have been investigated.Then on the basis,we have studied the growth mechanism and spatial orientation of substituted chloro-phenols in the silver colloidal solution.The following are the main research contents and conclusions:1.We have firstly studied the structure and spectral character a series of ginsenoside molecules combining theoretical calculation and experiment work.On the basis of the equilibrium geometry structures of four kinds of diol-type ginsenosides (Rh2,Rb3,Rd,Rg3) and three kinds of triol-type ginsenosides(Re,Rh1,Rg2) obtained with the B3LYP/6-311G level,the frequencies have been calculated and compared with the experimental ones.It can be seen that there is a good agreement between the calculated results with the experimental ones in the low wave number range.The elementary consistency of spectral signal can be due to their same aglycones in the ginsenoside.Simultaneously,the difference of spectrum can be owing to the different substituted positions for saccharide ring in diol-type and triol-type ginsenosides,the different number and kind of saccharide ring in the same group.The calculated results indicate that the structure is relatively stabile for there is five chiral carbon in the rigid ring of aglycones.So,the spectral signal is basically no large difference in this part for the two isomers.However,in the C20 position,the different spatial orientation of the four substituted groupslead to large change of bond length,bond angle correlative with C20,resulting in large impact on spectrums.Thus, the peaks pertinent to the vibration near the C20 can be as the characteristic spectrum peak.There is obvious difference for the infrared and Raman spectrums of diol-type ginsenosides group and triol-type ginsenosides one,respectively.Obviously,spectral technology is an effective method to distinguish ginsenoside,especially for different group of ginsenoside.2.The 6-311+G(d,p)and 6-311++G(df,pd) basis sets on the MP2,HF,B3LYP and BLYP levels in the Gaussian program,the equilibrium geometry structures and frequencies have been calculated for the 4-CP(4-Chlorophenol),2,6-DCP (2,6-dichlorophenol),2,4,6-TCP(2,4,6-Trichlorophenol),respectively.Then,with the triple-ξpolarized Slater type(TZP) basis set on the Becke-Perdew(BP86) XC-potential level in the ADF,the equilibrium geometry structures and frequencies have been calculated for the three molecules above-mentioned.The effect of the different positions and numbers of substituted groups on spectral signal has been analyzed.It can be confirmed that there exists induction effect among atoms in the phenol-ring and substituent,which its value depends the intensity of electronegativity of substituent.In addition,the reason for the large difference of the geometry structure and vibration frequency for 2,6-DCP and 2,4,6-TCP is the forming of the intramolecular hydrogen bond between substituent -Cl and O-H bond,which can induce the change of charge density distribution on atoms near the substituent.Due to the larger electron-accepted ability owing to the larger electronegativity of substituent -Cl relative to substituent -Br,there is large change of the charge density distribution on the phenol-ring of chlorophenol relative to that of phenol-ring of bromophenol, which can be the reason for the difference of the structures and spectrums of chlorophenol and bromophenol.3.With the 6-31+G^**(for C,H,Cl,O)/Lanl2dz(for Ag) basis set on B3LYP level,the structure and vibration frequency of molecules coming from the action 4-CP,2,6-DCP,2,4,6-TCP with Ag atom have been investigated.There is a good agreement between the calculated spectrums and experimental ones.The calculated results indicate that the chlorophenol molecule in Ag colloidal solution adsorbs on the surface of Ag atom by the tilting of O atom through some degree.There is longer bond length of O-Ag in the 2,6-DCP than that of 4-CP,which can be due to the substitution of Cl atom for H on the hydroxy ortho-position,increasing the steric hindrance of interaction of O atom and Ag one.However,there is no large change of the bond length of O-Ag from the 2,4,6-TCP to 2,6-DCP,which shows that the impact of the substituent -Cl on the para-position on the bond length of O-Ag is small.In addition,owing to the action of chlorophenol with Ag,the intensity of some peaks have been increased.Moreover,the intensity and position of these peaks exhibit some regularity.The intensity of some peaks obviously decrease with the subdued action of O atom with Ag one due to the increasing number of-Cl.