γ-Radiolysis of Poly(A) in Aqueous Solution: Efficiency of Strand Break Formation by Primary Water Radicals

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Abstract
γ-Radiation-induced single-strand break formation (ssb) in polyadenylic acid (poly(A)) has been determined in Ar and N2O-saturated aqueous solution in the presence of different concentrations of t-butanol. Strand breaks were monitored by a low-angle laser light-scattering technique. The efficiencies for strand breakage caused by solvated electrons, hydrogen atoms and OH radicals have been found to be 0·25, 0·20 and 7·8 per cent, respectively. The efficiency of OH radicals depends only slightly on pH (pH 5·0, 7·5 and 9·0) and is independent of the presence of salt (0·01 mol dm−3 NaClO4) and of the irradiation temperature (20°C and 70°C). The efficiency of OH for ssb formation obtained in this work with poly(A) is much smaller than that of poly(dA). This is explained by the different molecular conformations of the sugar moiety of poly(A) (3′-endo) and poly(dA) (2′-endo). With increasing t-butanol concentration more strand breaks are formed than expected from simple homogeneous competition kinetics of poly(A) and t-butanol for OH radicals. This result is considered to be due to nonhomogeneous reaction kinetics in the above-mentioned competition. The rate constants for the reaction of OH and H with poly(A) have been determined.