ENDOR and ESR studies of irradiated cytidine

Single crystals of cytidine have been x-irradiated and studied by electron nuclear double double resonance, electron nuclear double resonance, and electron spin resonance techniques at room temperature. One radical species was studied in detail and the results show anisotropic couplings of an unpaired electron to three hydrogen nuclei with the following principal values: a1, −66.3 MHz, −43.5 MHz, −20.7 MHz; a2, −68.9 MHz, −43.4 MHz, −20.3 MHz; a3, −37.2 MHz, −27.0 MHz, −13.6 MHz. The g tensor principal values are 2.0031, 2.0025, and 2,0021. These data indicate a radical formed in the ribose sugar group with spin density localized on C4′ and C5′.