title: E.s.r. and spin-trapping studies of dihydropyrimidines. gamma-Radiolysis in the polycrystalline state and U.V. photolysis in aqueous solution.
abstract: gamma-Radiolysis in the polycrystalline state and U.V. photolysis in aqueous solution at 220 nm of several dihydropyrimidines and their derivatives have been investigated by spin-trapping and electron spin resonance. 2-Methyl-2-nitrosopropane was used as the spin-trap. The spin-adducts of the 6-yl radicals obtained fall into two categories. Those from dihydro-1-methyluracil, dihydro-6-methyluracil, dihydro-1-ethyluracil and dihydro-1-methylcytosine exhibit a beta-nitrogen hyperfine coupling constant (alpha beta N) equal to or less than 2.0 G while the ones fom dihydro-orotic acid, dihydrouracil and dihydrothymine showed much larger alpha beta N values (greater than 3.3 G). Dihydrouridine gives radicals characteristic of both the dihydropyrimidine ring and the sugar moiety. The same radicals were obtained by gamma-radiolysis or U.V. photolysis. For all the 5-yl radicals obtained by U.V. photolysis, a direct photoexcitation mechanism is proposed.
mesh_terms: D003460:Crystallization; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D005720:Gamma Rays; D010782:Photolysis; D011743:Pyrimidines / Q000528:radiation effects; D012996:Solutions; D014466:Ultraviolet Rays
chemical_list: D005609:Free Radicals; D011743:Pyrimidines; D012996:Solutions