Radicals Produced by γ-Irradiation of Hyperquenched Glassy Water Containing 2′-Deoxyguanosine-5′-monophosphate

Abstract

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(*) and HO2(*) radicals generated by water radiolysis, three species are trapped at 77 K:(i) G(C8)H(*) radical, the H-adduct to the double bond at C8; (ii) G(- *) radical anion, the product of electron scavenging by the aromatic ring of the base; and (iii) dR(-H)(*) 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(*) radicals, in a concerted process following ionization of water molecule at L-type defect sites of the H-bonded matrix. The lack of OH(*) reactivity toward the solute suggests that the H-bonded structure in HGW is much more effective in recombining OH(*) radicals than that of aqueous glasses obtained from highly concentrated electrolyte solutions. Furthermore, complementary experiments for the neat matrix have provided evidence that HO2(*) radicals are not the product of H atom reaction with molecular oxygen, possibly generated by ultrasounds used in the process of sample preparation.

Photoinduced formation of peroxyl radicals in aqueous solutions of nucleobase derivatives at 77 K

“…(5) G -• are anion radicals of G; we used a spectrum identical to that of A -• , since the parameters of spectra of A and G anion radicals were identical, according to the data from [23]. This signal virtually coincides with the one calculated in [24].…”

“…(HGW glasses favor this reaction since the number of L-defects is higher in them than in normal ice [24]). We may assume that our systems are also favor reaction (2) for two reasons.…”