Radiation-Chemical Studies of the Reaction of ${\rm S}\dot{{\rm O}}_{4}{}^{-}$ with Uracil and Its Derivatives

Several radiation-chemical methods have been used to study the reaction of ${\rm S}\dot{{\rm O}}_{4}{}^{-}$ with uracil, isoorotic acid, and thymine. Pulse radiolysis with spectrophotometric detection has shown that the products in neutral solution absorb well beyond 500 nm and in each case are different from those produced by OH reaction. The spectrum of the radical from uracil has peaks at 410 and 560 nm with calculated extinction coefficients of 1000 and $750\ M^{-1}\ {\rm cm}^{-1}$ respectively. The spectrum obtained with thymine is similar while that obtained with isoorotic acid shows a single peak at 470 nm with an extinction coefficient of $2200\ M^{-1}\ {\rm cm}^{-1}$. Conductometric experiments show that release of a proton accompanies radical formation. The ESR spectra obtained in steady-state radiolysis experiments with uracil and isoorotic acid are characterized by g factors of about 2.0044. These radicals represent the acidic forms of radicals previously observed to be formed by OH in basic s...