Radicals Produced in Single Crystals of Thymine Derivatives by UV and X-Rays

Abstract

Abstract Single crystals of anhydrous thymine (T), thymine monohydrate (T · H2O), 5,6-dihydrothymine (TH2), 1-methylthymine (mT) and thymidine (dT) were irradiated with X-rays and UV between 77 K and 300 K. Six types of radicals were analyzed by ESR-spectroscopy at 9.5 GHz and 35 GHz after exposure to X-rays. The anion radical occurred only in T · H2O at 77 K, the 4-yl radical only in TH2 at 77 K and the 1-yl radical only in T between 77 K and 300 K. The 6-yl radical was found in T, TH2 and mT. It was converted into the 5-yl radical irreversibly by heat or white light (λ < 600 nm). The 5-yl radical appeared in all compounds at room temperature. The highest thermal stability was found for the 7-yl radical which was present at room temperature in all compounds except TH2.UV-irradiation (λ = 320 nm) produced radicals only in three crystals (T, TH2, dT). In T the 5-yl radical was found after exposure at 300 K, and two other radicals, 1-yl and 7-yl, at 77 K. Also at 77 K, the 7-yl radical was present in dT and the 5-yl radical in TH2 and dT.