The structure of mirror 14 C and 14 O nuclei has been studied in the framework of the fiveparticle model (three α-particles and two nucleons). Interaction potentials are proposed, which allowed the energy and radius of 14 C nucleus, as well as the energy of 14 O one, to agree with experimental data. On the basis of the variational approach with the use of Gaussian bases, the energies and wave functions for five-particle systems under consideration are calculated. The charge radius of 14 O nucleus, as well as the charge density distributions and the form factors for both nuclei, are predicted. K e y w o r d s: root-mean-square radius, density distribution, charge form factor, 14 C nucleus, 14 O nucleus.

Changes in the medium of biological cell nucleus under ion beam action is considered as a possible cause of cell functioning disruption in the living body. As the most long-lived molecular product appeared in the cell after the passage of high energy ions, the hydrogen peroxide molecule is picked out. The possibility of the formation of stable complexes of hydrogen peroxide molecules with active sites of DNA nonspecific recognition (phosphate groups of the double helix backbone) is studied, and the formation of stable DNA-peroxide complexes is considered. Due to the negative charge on the oxygen atoms of DNA phosphate group in solution the counterions that under natural conditions neutralize the double helix have been also taken into consideration. The complexes consisting of oxygen atoms of DNA phosphate group, H 2 O 2 and H 2 O molecules, and Na + counterion have been considered. Energy of the complexes have been determined based on the electrostatic and van der Waals interactions within the approach of atom-atom potential functions. The stability of various configurations of molecular complexes has been estimated. It has been found that hydrogen peroxide molecules can form the stable complexes with phosphate groups of DNA and counterions which are no less stable than the complexes with water molecules. It is shown that the formation of stable complexes of H 2 O 2 -Na + -PO − 4 can be detected experimentally by the observation of specific DNA vibrations in the low-frequency Raman spectra. The interaction of H 2 O 2 molecule with phosphate group of the double helix backbone can block the processes of DNA biological functioning and induce the deactivation of the genetic apparatus of the cell. Thus, the new channel of high-energy ions action on living cell has been proposed.

After irradiation of cancer cells in the ion beam therapy method the concentration of hydrogen peroxide in the cell medium grows significantly. But the role of hydrogen peroxide molecules in cancer treatment has not been determined yet. We assume that interaction of peroxide molecules with DNA atomic groups can block the genetic information of the cancer cell and lead to its neutralization. To understand the possibility of DNA deactivation in the cell, in the present study the formation of complexes of hydrogen peroxide molecules with DNA specific recognition sites (nucleic bases) is considered. Using atom-atom potential functions method and quantum-chemical approach, based on density functional theory, the spatial configurations and energy minima for the complexes of peroxide and water molecules with nucleic bases are studied. The most probable positions of hydrogen peroxide molecules interacting with nucleic bases are determined, and the possibility of blocking of genetic information transfer processes is shown. The obtained data allows us to formulate a new mechanism of the ion irradiation action on living cells, that can be useful for cancer treatment.

Background: Molecules of hydrogen peroxide (H 2 O 2) can be formed during radiolysis process in water medium after irradiation. A hypothesis about the possible role of hydrogen peroxide in blocking of processes of nonspecific DNA recognition by proteins is proposed in [1]. As one of the most long-living products, H 2 O 2 molecules can diffuse considerable distances in the intracellular medium and reach DNA in the cell nucleus and form complexes with macromolecule phosphate groups. To confirm this hypothesis, the quantum chemical calculations of complexes structure of hydrogen peroxide molecule with atomic groups of the DNA backbone are performed. Objectives: To determine the optimal geometries and formation energies of stable complexes of hydrogen peroxide with DNA phosphate group. To perform a comparative analysis of hydrogen peroxide and water molecules binding to phosphate group based on quantum chemical calculations. Materials and Methods: The complexes which consist of phosphate group, hydrogen peroxide, water molecules, and sodium counterion are analyzed. The optimization of complex geometry and energy calculations is performed using the methods of quantum chemistry within Gaussian 03 software: HF/6-31+G(d,p), MP2/6-31+G(d,p), B3LYP/6-31+G(d,p). Results: This research shows that the hydrogen peroxide molecule as well as water molecule can form stable complexes with phosphate group, especially with the presence of sodium counterion Na +. The results of complex formation calculations with atom-atom potential functions method are confirmed. It is shown that the presence of sodium counterion significantly influences the geometry of the hydrogen peroxide complex with the phosphate group. The performed calculations indicate the possibility of hydrogen peroxide geometry change in the processes of complex formation. Conclusions: The obtained results confirm the possibility of stable complexes forming for hydrogen peroxide and phosphate group. Prolonged situation of H 2 O 2 molecule near the DNA backbone may block the nucleic-protein recognition processes as well as damage the macromolecule via decay into OHradicals in close proximity to double helix.