Study On The Structure And Property Of As-nucleobases Compounds

The studies about the interaction between arsenic atom and nucleobases are helpful to investigate the physiology process of arsenic atom and the micro-mechanism of biological function of nucleic acids. In this thesis, the ground state structures, harmonic vibrational frequencies, charge distribution, electron affinities, and formation energies for the compounds formed between arsenic atom and five nucleobases (adenine, guanine, cytosine, thymine, and uracil) have been investigated systematically with B3LYP method and DZP++ basis set. The result reveals that R-As-H form (R= nucleobases radical) is characteristic geometry of As-nucleobaeses and their anions. For neutrals, a strong association between arsenic atom and nucleobases is found and the ground state structures are R-As-H (R=nucleobases radical) complexes. For anions, the most stable structures are also R-As-H forms, but the association sites of arsenic atom with the exception of As-adenine are different from corresponding neutrals because intramolecular As-transfer is occurrence when the ground state structures of As-nucleobases change from neutral to anion. Natural population analysis (NPA) calculations indicate that more than 80% of extra electron is localized on the arsenic atom. Three types of electron affinity presented in this thesis are the adiabatic electron affinity (EAad), the vertical electron affinity (EAvert), and the vertical detachment energy (VDE). The calculated EAad values without ZPVE correction for the As-adenine, the As-guanine, the As-cytosine, the As-thymine, and the As-uracil are 2.07 eV, 2.12 eV, 2.38 eV, 2.55 eV, and 2.52 eV, respectively (ZPVE corrected values are 2.07 eV, 2.15 eV, 2.39 eV, 2.56 eV, and 2.55 eV, respectively). The EAvert values are from 1.62 eV to 1.98 eV, and the VDEs range from 2.15 eV to 2.74 eV. The formation energies of these complexes are estimated in order to examine relative stabilities. The calculated formation energies range from ?27.0 kcal/mol to ?23.1 kcal/mol. It indicates that the interation between arsenic atom and nucleobases is strong. The stability order is As-guanine > As-adenine > As-uracil > As-cytosine > As-thymine.