| Thymine is part of the A-T base pair(adenine-thymine)in DNA,They are paired with each other,forming two hydrogen bonds,making the DNA double helix structure more stable.It is an important component of genetic material,also the synthesis of many anti disease drugs key synthetic ingredients,It is important that whether in biological genetics or in medicine.So the structure characteristics of thymine,has important significance.In this paper,the ground state structure and infrared spectra of the thymine water clusters,and on the surface of the surface of the thymine clusters surface-enhanced Raman spectra are calculated by density functional theory in Quantum Chemistry.The paper is divided into five parts:The first part describes the nature and purpose of thymine,the role of hydrogen bonds and the principle of infrared spectrum,the surface enhanced Raman spectrum mechanism.In the second part,the quantum chemistry calculation method,the Gauss software,density functional theory and AIM software are introduced.And the calculation of Raman scattering intensity is explained.In the third part,the ground state structure and infrared spectra of the C5H6N2O2·(H2O)n(n=1~4)clusters are calculated by density functional theory(DFT)at the B3 LYP complex function in Gaussian09 W.The stable structures of C5H6N2O2·(H2O)n(n=1~4)clusters can be obtained by optimizing its structure.AIM program analysis shows that the format ion of hydrogen bonds between clusters,and the intensity of electron density also reflects the siz e of the red-shifted and blue-shifted.The vibrational infrared spectrum of C5H6N2O2.(H2O)n(n=1~4)clusters is analyzed by using the Veda4 and also compared the vibration frequency.The infra red spectra of the four most stable clusters molecules shows the formation of O–H…O or N–H…O H-bond makes the vibration frequency between O–H or N–H decrease and lead the vibration f requency red-shifted,while O–H...N H-bond makes the vibration frequency between O–H increa se and lead the vibration frequency blue-shifted.In the fourth part,The structures,surface-enhanced Raman scattering(SERS)and pre-resonance Raman spectra(SERRS)of C5H6N2O2-Agn(n=1~6)complexes were calculated using density functional theory(DFT)with the 6-311++G(d,p)(C,H,O)/Lan L2DZ(Ag)basis set.The results showed that the surface-enhanced Raman spectra has enhanced,SERS is still due to the chemical changes induced polarization enhancement.The SERRS spectra of the three complexes were obtained by excitation at 385,417 and 388 nm,which were close to the electronic excitation energy of absorption spectra as determined by time-dependent densityfunctional theory(TDDFT).The SERRS enhancement factors caused by the electrons in the Ag cluster to the thymine molecule π* bond orbital transition.And the charge-transfer excitation resonance were about 104,which corresponds to the Ag–O stretching.In the fifth part,summarize the full text. |
