Neutron-induced free radicals in oriented DNA

Area of Science:

• Molecular Biophysics
• Radiation Chemistry
• DNA Damage Mechanisms

Background:

• Understanding DNA's response to radiation is crucial for radiobiology and radiation protection.
• The structure and orientation of DNA can influence its susceptibility to radiation-induced damage.
• Electron spin resonance (e.s.r.) spectroscopy is a powerful tool for detecting and characterizing free radicals formed in biological molecules.

Purpose of the Study:

• To investigate the influence of neutron irradiation direction on radical formation in oriented DNA.
• To identify specific DNA radicals (thymine, guanine) and their formation pathways under different irradiation conditions.
• To elucidate the role of protonation in the formation of thymine radicals.

Main Methods:

• Irradiation of oriented DNA samples (30% water content) with neutrons at cryogenic temperatures (77 K).
• Analysis of electron spin resonance (e.s.r.) spectra to identify and quantify radical species.
• Comparison of e.s.r. spectra obtained from neutron irradiation parallel versus perpendicular to the DNA helix.

Main Results:

• Neutron irradiation of oriented DNA at 77 K yields distinct e.s.r. spectra based on neutron incidence angle.
• Perpendicular neutron incidence primarily results in thymine anion (T-.) and guanine cation (G+.) radicals.
• Parallel neutron incidence additionally produces a thymine hydrogen addition radical (TH.), suggesting protonation of T-.

Conclusions:

• The orientation of DNA relative to incident neutrons significantly affects the types and distribution of radiation-induced radicals.
• The formation of the TH. radical is dependent on neutron direction and likely involves a protonation mechanism.
• These findings provide insights into the anisotropic nature of DNA radiation damage at a molecular level.