Electronic properties of DNA-related molecules containing a bromine atom

Abstract

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.

Keywords:

• Brominated DNA
• X-ray absorption fine structure
• X-ray photoelectron spectroscopy
• specific heat capacity

Acknowledgements

The spectroscopy experiments were performed with the approval of the Photon Factory Program Advisory Committees (proposal numbers 2017G681), and Hiroshima Synchrotron Radiation Center of Hiroshima University (proposal numbers: 18AG008, 18BG019, 19AG033, 19BG021).

Disclosure statement

The authors report no declaration of interest. The authors alone are responsible for the content and writing of the paper.

Additional information

Funding

This work was supported by QST President's Strategic Grant (QST Advanced Study Laboratory).

Notes on contributors

Misaki Hirato

Misaki Hirato, is pursuing an MSc in the partner graduate school program of Ibaraki University with National Institutes of Quantum and Radiological Sciences and Technology, and studies the electronic properties of DNA-related molecules using synchrotron spectroscopy techniques.

Misato Onizawa

Misato Onizawa, holds an MSc from the partner graduate school program of Ibaraki University with National Institutes of Quantum and Radiological Sciences and Technology, and was investigating biophysical nature of DNA-related molecules.

Yuji Baba

Yuji Baba, is a Visiting Scientist of QST and JAEA, and does research on surface chemistry using synchrotron-based spectroscopies such as X-ray photoelectron spectroscopy and X-ray absorption spectroscopy.

Yoshinori Haga

Yoshinori Haga, is a Principal Researcher in Advanced Science Research Center, Japan Atomic Energy Agency, and investigate electronic properties of strongly correlated actinide materials.

Kentaro Fujii

Kentaro Fujii, is a Senior Principal Researcher in Institute for Quantum Life Science, National Institutes of Quantum and Radiological Sciences and Technology, and does spectroscopic research of biomolecules using synchrotron soft X-rays.

Shin-ichi Wada

Shin-ichi Wada, is an Associate Professor of Graduate School of Advanced Science and Engineering in Hiroshima University, and supervises outstanding projects in atomic and molecular photo-dynamics using advanced highly brilliant soft X-ray sources.

Akinari Yokoya

Akinari Yokoya, is a Senior Principal Researcher in Institute for Quantum Life Science, National Institutes of Quantum and Radiological Sciences and Technology, and a Visiting Professor at the partner graduate school program of Ibaraki University, and supervises various projects in radiation biology and radiation-biophysics.