Raman Spectroscopy Study Of Cyclobutane Pyrimidine Dimmer

This paper based on the density functional theory (DFT), using the method of B3LYP/6-311G (d,p)(C, H, O atoms) and Lanl2dz (Ag atom) and Gaussian03application program. In this paper, we calculation the normal Raman spectroscopy (NRS) of pyrimidine monomer and DNA light damage product-cyclobutane pyrimidine dimer, and surface-enhanced Raman scattering (SERS)of the complex structure adsorbed on Ag nanoparticles. According to the calculated result, we get:With the vanish of the C5=C6bond in the dimer, It stretching vibration bands got narrower significantly, and the property got weakened, So, the Cyclobutane of tetratomic ring:C5-C5'-C6-C6', the stretching vibration mode and the ring deformation vibration mode had arisen.This can be used as a way of detection for the photodamage of DNA.For the Pyrimidine monomer and Cyclobutane pyrimidine dimers, the most favorable adsorption site of Ag Nanoparticle is O7.The Raman spectral bands, that is, the Ring breathing vibration mode and close to the Silver atoms (N1,N3,C6,C2=O), it will be got stronger in the SERS.From the selective enhancement rule of the SERS we know,The selective of Vertical adsorption also get stronger,And the closer to the adsorption surface, and the stronger. Therefore,we speculated that the Pyrimidine molecule and the dimer can vertical adsorption in the surface of silver nanoparticles through the O7atom.For the complex Th-Ag,the strength of N-H flexural vibrations and stretching vibration had a noticeable enhancement, And the maximum enhancement factor is about12times.For the complex Th2-Ag,correspond to C2=O stretching vibration,the maximum enhancement factor is about18times. For the complex U-Ag,the bending vibration and stretching vibration intensity have also significantly enhanced in-plane of N-H, and the maximum enhancement factor is about40times.For the complex U2-Ag, correspond to C2=O stretching vibration, the maximum enhancement factor is about17times.And on the surface, the Raman scattering enhancement mechanism is due to the static chemical enhancement.That is because,when the pyrimidine monomer and dimer adsorpted to the silver atom, between the molecules and silver atoms were redistributed, and caused the rate of static polarization to change. The rate of the static polarization changed is very important to the Raman scattering enhancement, the greater the rate of change, the more active.The absorption spectra and pre-resonance Raman spectra (SERRS) of Th2-Ag and U2-Ag complexes are calculated by time-dependent TDDFT methods at B3LYP/6-311G (d,p)(C,H,O)/Lanl2dz (Ag) basis set. The SERRS of the two complexes are obtained at316nm and315nm incident light. The results show that the SERRS enhancement factors of the v C=O vibrational model in the two complexes are found to103, the enhancement factors of the β N-H vibrational model in the two complexes are found to103-104, while the SERRS enhancement factors of the v Ag-O vibrational model are about104, mainly caused by the charge-transfer excitation resonance.This paper provided Raman spectroscopy detection of DNA lesions and damage with related parameters, it has very vital significance to the DNA and the RNA pathological change mechanism and the damage examination.