SELECTIVE DNA THYMINE DIMERIZATION DURING UVA IRRADIATION IN THE PRESENCE OF A SATURATED PYRIDOPSORALEN

Abstract— It has been recently shown that UVA (320–400 nm) irradiation of DNA in the presence of pyridopsoralens induces the formation of thymine cyclobutane dimers in addition to monoadducts. In this work, we measured the potency of a saturated pyridopsoralen to photosensitize DNA, despite its inability to covalently attach to DNA. First, from spectroscopic fluorescence measurements, we have shown that both analogs, saturated and unsaturated pyridopsoralens, namely 4',5'-dihydro-7-methyl-pyrido[3,4-clpsoralen (DH-MePyPs) and 7-methylpyrido[3,4-c]psoralen, exhibit a similar global affinity for DNA. Secondly, we demonstrated, by footprinting experiments, that exposure of a DNA sequence to 365 nm UV radiation in the presence of DH-MePyPs results in selective cyclobutane thymine dimerization. Thymines located in the immediate proximity of the 5'-TA-3' step are exclusively affected and the frequency of this photoprocess depends on flanking sequences. We thus probe a selective thymine dimer photosensitizer. Results are discussed in terms of drug affinity and physical properties of the helix at the binding site.     

Using a 120-cm cyclotron to study the combined effects of ionizing radiation and hypomagnetic conditions on lettuce seeds

The impact of ionizing radiation and hypomagnetic conditions on seeds of the lettuce Lactuca sativa L. is studied on the 120-cm cyclotron at the Skobeltsyn Institute of Nuclear Physics. The seeds are irradiated with α-particles with energies of around 25.8 MeV and placed to germinate in a hypomagnetic chamber under conditions of an attenuated (up to 2500 times) geomagnetic field. Chromosomal aberrations in the first mitosis of the root meristem are analyzed. Changes in the irradiated samples are observed when compared to control samples. Hypomagnetic conditions greatly magnify the negative impact of ionizing radiation.     

Generation of wave process in the Belousov-Zhabotinsky reaction by a 30-MeV collimated electron beam

The generation of leading centers in the Belousov-Zhabotinsky reaction by a 30-MeV collimated electron beam has been investigated. The center generation threshold is estimated to be 2.0 ± 0.5 kGy.     

Influence of 30-MeV α-particle beams on wave propagation in the Belousov-Zhabotinsky reaction

The generation of leading centers in the Belousov-Zhabotinsky reaction under the action of collimated radiation with a high linear energy transfer has been investigated. To get insight into the mechanism of the effect of radiation on the Belousov-Zhabotinsky reaction, the radicalator model was modified to involve the interaction of the reactants with the ^•OH radical produced by water radiolysis.     

Numerical simulation of energy relaxation processes in a ZnMoO<Subscript>4</Subscript> single crystal

We present the results of our experimental investigation and numerical simulation of excitation-energy relaxation processes in zinc molybdate crystals. We show that our kinetic model of the energy relaxation makes it possible to describe basic features of experimental results. Using this model, we estimate the trap concentration in ZnMoO₄ upon irradiation of the crystal by VUV synchrotron radiation and X-ray radiation. We conclude that prolonged phosphorescence of ZnMoO₄ that is observed after irradiation of the crystal by X-ray radiation can be caused by the occurrence of additional traps with a low activation energy.     

Populations of sublevels 24Mg(2+) nucleus formed in the reaction 24Mg(d,d1γ)24Mg at E d = 15.3 MeV

Angular dependences of density matrix spin tensors and sublevel populations are experimentally reconstructed for the ²⁴Mg(2⁺, 1.369 MeV) nucleus formed in the inelastic scattering of deuterons by ²⁴Mg at E _d = 15.3 MeV and deuteron emission angles from 25° to 165° (lab). The experimental results are compared to those from calculations using different versions of the coupled-channel method.     

Tensor features and dynamical deformation of the 24Mg(2+) nucleus in the reaction 24Mg(d,dγ)24Mg at E d = 15.3 MeV

The results obtained by reconstructing of the experimental angular dependences of polarization tensors, the tensors of orientation of multipole moments, and the dynamical deformation of ²⁴Mg nuclei produced in the 2⁺ state at 1.369 MeV in inelastic deuteron scattering on ²⁴Mg nuclei at E _d = 15.3 MeV for deuteron scattering angles between 25° and 165° in the laboratory frame are presented. The experimental results are compared with the results of calculations based on various versions of the coupled-channel method. The role of spin-orbit and tensor d ²⁴Mg interactions is discussed along with the influence of the reorientation effect. The correlation features of the 2⁺ state of the ²⁴Mg nucleus at 1.369 MeV that were determined in inelastic deuteron and alpha-particle scattering on ²⁴Mg are compared.     

Luminescence of excitons and antisite defects in the phosphors based on garnet compounds

Intrinsic emission (excitons, anti-site defects (AD)) of oxides with garnet structure has been analysed by means of investigation of the time resolved luminescence and decay kinetic spectra under excitation by the synchrotron and X-ray radiation at 10–300 K of the model objects: undoped single crystals and single crystalline films of Y₃Al₅O₁₂ and Lu₃Al₅O₁₂ garnets which are characterised by the significant differences in concentrations of AD Y_Al³⁺ and Lu_Al³⁺-types as analogs of cation isoelectronic impurities.     

Heterogeneous Reaction of Dimethyl Sulfide with Iodine Oxide in a Temperature Range of 291–365 K

Kinetics and Catalysis - A reaction of the iodine oxide (IO) radical with dimethyl sulfide (DMS) in a temperature range of 291–365 K was studied using atomic iodine resonance fluorescence. It...