Electron Nuclear Double Resonance (ENDOR) approach for studying radiation damage in DNA

The ultimate ambition of this project was to perform an EMR study of radiation-induced radicals on DNA samples, comparably successful as for sucrose. This would provide the most direct way to determine the precise role of sugar radicals in radiation damage to DNA. Mainly because of the lack of DNA single crystals (DNA fibers are only partially oriented), literature studies have so far been restricted to EPR studies of polycrystalline or frozen solution DNA, with high risk of erroneous conclusions based only on isotropic parameters, as the UGent group could demonstrated e.g. for the carbohydrate trehalose. This could be avoided if information on the anisotropy of g and hyperfine tensors is collected for confrontation with DFT calculations. Therefore we explored the possibilities of powder ENDOR (and/or pulsed EPR), first on DNA-related materials and in the later stages of the project the first attempts on DNA have also been made. It is known, but still remarkable that anisotropic information can be retrieved from powder materials exploiting the orientation selectivity of ENDOR and pulsed EPR. Before tackling DNA, we have started our research on sucrose and alanine.

Sucrose is used as a test case where both single crystal and powder EMR spectra can be directly compared, taking advantage of the detailed and reliable knowledge, and experience gained already in the past few years. Being universally present, sucrose is most promising for dosimetry and nowadays the best understood sugar in this context. Between 2000 and 2020 we could identify four RT stable radicals in sucrose, after characterizing them in great detail via their g and 1H hyperfine tensors obtained by ENDOR-based techniques. This led to the most reliable reproduction to-date of the experimental EPR powder spectrum of irradiated sucrose, using the single crystal spin Hamiltonian parameters of the four aforementioned radicals. In the course of this project, methodology has also been developed to reconstruct powder EPR spectral components related to specific ENDOR transitions by following the powder ENDOR intensity as a function of magnetic field, this is ENDOR-induced-EPR for powder samples.

The results of this project are bundled in the PhD thesis of Jevgenij Kusakovskij . This research line is no longer active at this moment. Radiation effects in solids and radiation detection materials remain a topic of interest, though.

Selected publications:

ENDOR-induced EPR of disordered systems : application to X-irradiated alanine

Jevgenij Kusakovskij (UGent) , Kwinten Maes (UGent) , Freddy Callens (UGent) and Henk Vrielinck (UGent)

(2018) JOURNAL OF PHYSICAL CHEMISTRY A. 122(6). p.1756-1763

On the identity of the last known stable radical in X-irradiated sucrose

Jevgenij Kusakovskij (UGent) , Hendrik De Cooman (UGent) , Einar Sagstuen, Freddy Callens (UGent) and Henk Vrielinck (UGent)

(2017) CHEMICAL PHYSICS LETTERS. 674. p.6-10