The interaction of ionizing radiation with DNA and its hydration layer
results in the production of free radical species trapped on either the
bases or sugar phosphate backbone of the DNA. The objective of this work
is to identify the radicals generated in hypoxanthine and its derivatives.
Hypoxanthine is a purine and is closely related to DNA subunits that differ
by the arrangement of hydrogens in the molecule. Single crystals of hypoxanthine
derivatives were X-irradiated and investigated using K-band (24 GHz) electron
paramagnetic resonance (EPR), electron-nuclear double resonance (ENDOR),
and field-swept-ENDOR (FSE) techniques at 10 K. Immediately following irradiation
at 10 K at least three different radicals were observed for hypoxanthine·HCl·H2O.
For unique assignment of observed hyperfine couplings, partially deuterated
crystals of hypoxanthine·HCl·H2O where used. Identified radicals
are the N3?protonated anion radical and the N7-deprotonated cation radical.
For inosine, the nucleoside of hypoxanthine base, at least five different
radicals are formed immediately after irradiation at 10 K. Two of these
were identified as the N1-deprotonated anion radical and C5’-H abstraction
radical at the sugar ring. Evidence indicates that the third radical may
be the O6-protonated anion. Analysis of the spectra following warming both
hypoxanthine and sodium inosine crystals to room temperature showed that
C8-H addition radical is the only observable radical.