Incorporation of a bromine atom into DNA-related molecules changes their electronic properties.

To understand the mechanism underlying the high radio-sensitisation of living cells possessing brominated genomic DNA, X-ray photoelectron spectroscopy (XPS) using synchrotron X-rays with energies of 2000 or 2500 eV was used to study brominated and nonbrominated nucleobases, nucleosides and nucleotides. The bromine atom significantly reduced the energy gap between the valence and conduction states, although the core level states were not greatly affected. This finding was supported by quantum chemical calculation for the nucleobases and nucleosides. Our findings strongly indicate that the energy gaps between the valence and conduction levels of the molecules are significantly reduced by bromination. Furthermore, the brominated molecules are more likely to produce inelastic scattering low energy electrons upon exposure to 2000 or 3000 eV X-rays. This modification of electronic properties around the brominated group may both facilitate electron transfer to the brominated site in DNA and increase the probability of reaction with low energy electrons. These processes can induce DNA damage, presumably resulting in debromination of the uracil moiety and a subsequent cytotoxic effect.

Electronic properties of DNA-related molecules containing a bromine atom.

PURPOSE: To clarify the radiosensitization mechanism masking the Auger effect of the cells possessing brominated DNA, the electronic properties of DNA-related molecules containing Br were investigated by X-ray spectroscopy and specific heat measurement. MATERIALS AND METHODS: X-ray absorption near-edge structure (XANES) and X-ray photoemission spectroscopy (XPS) were used to measure the electronic properties of the nucleotides with and without Br. We determined the specific heat of 5-bromouracil crystals with thymine as a reference molecule at low temperatures of 3-48 K to calculate the microscopic state numbers. RESULTS: Obtained XANES and XPS spectra indicated that both the lowest unoccupied molecular orbital (LUMO) and the core-levels were not affected by the Br incorporation. The state numbers of 5-bromouracil calculated from the specific heats obtained around 25 K was about 1.5 times larger than that for thymine below 20 K, although the numbers were almost the same below 5 K. DISCUSSION: Our results suggest that the Br atom may not contribute substantially to the LUMO and core-level electronic states of the molecule, but rather to the microscopic states related to the excitation of lattice vibrations, which may be involved in valence electronic states.

Evaluation of the Foveal Avascular Zone in Familial Exudative Vitreoretinopathy Using Optical Coherence Tomography Angiography.

PURPOSE: To evaluate the foveal avascular zone (FAZ) and retinal structure in familial exudative vitreoretinopathy (FEVR). PATIENTS AND METHODS: Eighteen eyes with stage 1 or 2 FEVR and 20 control eyes were evaluated. The central retinal thickness (CRT), foveal inner retinal thickness (IRT), surface retinal vessel density (SRVD), and deep retinal vessel density (DRVD) were measured using optical coherence tomography. The FAZ area was calculated using ImageJ software. The equivalent spherical value (SE) and axial length (AL) were measured. RESULTS: The CRT (232.5±3.086 vs 211±12.6325 µm; p=0.003) and foveal IRT (15.83±13.95 vs 0.9±4.02 µm; p=0.002) were thicker in the FEVR group than in the control group. The surface FAZ area (0.265±0.08 vs 0.364±0.09 mm2; p=0.004) and the deep FAZ area (0.364±0.1 vs 0.484±0.11 mm2; p=0.03) were smaller in the FEVR group than in the control group. The SRVD values did not differ among the sectors, but the DRVD was higher in the FEVR group except for the inferior sector (superior, p=0.027; inferior, p=0.88; temporal, p=0.035; nasal, p=0.027). The SE and AL did not differ between the two groups. There were no correlations between the surface and deep layer FAZ area and age, CRT, SE, and AL. The surface, deep FAZ area, and foveal IRT were correlated negatively (surface, r = -0.47, p=0.033; deep layer FAZ area, r = -0.46, p=0.037). CONCLUSION: Eyes with FEVR have a smaller FAZ because the vascular structure in the inner retina remained in the fovea.