Radicals produced by gamma-irradiation of hyperquenched glassy water containing 2 '-deoxyguanosine-5 ' monophosphate

Hyperquenched glassy water (HGW) has been suggested as the best model for liquid water, to be used in low-temperature studies of indirect radiation effects on dissolved biomolecules (Bednarek et al. J. Am. Chem. Soc. 1996, 118, 9387). In the present work, these effects are examined by X-band electron spin resonance spectroscopy (ESR) in gamma-irradiated HGW matrix containing 2'-deoxyguanosine-5'-monophosphate. Analysis of the complex ESR spectra indicates that, in addition to OH center dot and HO2 center dot radicals generated by water radiolysis, three species are trapped at 77 K: (i) G(C8)H-center dot radical, the H-adduct to the double bond at C8; (ii) G(-center dot) radical anion, the product of electron scavenging by the aromatic ring of the base; and (iii) dR(-H)(center dot) radicals formed by H abstraction from the sugar moiety, predominantly at the C'5 position. We discuss the yields of the radicals, their thermal stability and transformations, as well as the effect of photobleaching. This study confirms our earlier suggestion that in HGW the H atom addition/abstraction products are created at 77 K in competition with HO2 center dot radicals, in a concerted process following ionization of water molecule at L-type defect sites of the H-bonded matrix. The lack of OH center dot reactivity toward the solute suggests that the H-bonded structure in HGW is much more effective in recombining OH center dot radicals than that of aqueous glasses obtained from highly concentrated electrolyte solutions. Furthermore, complementary experiments for the neat matrix have provided evidence that HO2 center dot radicals are not the product of H atom reaction with molecular oxygen, possibly generated by ultrasounds used in the process of sample preparation.