To investigate the detailed mechanism underlying double-stranded DNA (dsDNA) breaks caused by electron or photon impact, a physical model is proposed and ab initio quantum chemical calculation is employed. In our model, we neglect the backbone of DNA and focus on the interaction between a hydroxyl radical and a single-base pair. By Becke's threeparameter hybrid Lee-Yang-Parr (B3LYP) functionals method based on a density functional theory, we calculate the optimized structure of base pair-hydroxyl radical complex by the energy minimization. The results suggest that the hydroxyl radical can stably exist near the hydrogen bond between adenine and thymine, or between guanine and cytosine. Consequently, we have found that the hydroxyl radical weakens the hydrogen bonds and the corresponding bond length of the base pair in dsDNA increases.

ABSTRACT:Hund's spin-multiplicity rule for the ground state of the methylene molecule CH 2 is interpreted by Hartree-Fock (HF) and multi-reference configuration interaction (MRCI) methods. The stabilization of the triplet ground state (X 3 B 1 ) relative to the second singlet excited state (b 1 B 1 ) is ascribed to the greater electron-nucleus attraction energy that is gained at the cost of increasing the electron-electron repulsion energy and with the aid of a reduction in the nucleus-nucleus repulsion energy. The highest spin-multiplicity in the ground state of CH 2 is accompanied by a set of three characteristic features, i.e., elongation of the internuclear distances, reduction in the bond angle, and contraction of the valence electron density distribution around the nuclei involving expansion of the core electron density distribution. The present calculations fulfill the virial theorem to an accuracy of −V/T = 2.000 for both HF and MRCI. Accordingly, the molecular geometries are optimized for each of the two states. The inclusion of correlation by MRCI method reduces the energy splitting between the two states by about 14%. The energy splitting is analyzed by the correlational virial theorem 2T c + V c = 0 to make a clear interpretation of the correlation effect.

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In order to determine the electric quadrupole moment of the short-lived Remitter 41 Sc from the quadrupole coupling constant in Ti0 2 , we measured the field gradient by detecting the Fourier-Transformed-NMR of stable isotope 45 Sc doped in TiO->. Also, in order to study the electronic structure of impurities systematically, EFGs were measured for * 5 Sc, 49 Ti and 93 Nb in a Ti0 2 single crystal.

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