ENDOR study of the 3αH radical in deoxycytidine 5′-phosphate⋅H2O

The dominant radical observed at room temperature in x-irradiated deoxycytidine 5′-phosphate monohydrate (5′dCMP) shows anisotropic hyperfine coupling to three α hydrogens. The principal values of these three couplings, determined by an ENDOR experiment, are α (1):−18.77, −42.96, −71.16 MHz; α (2):−19.15, −44.24, −67.18 MHz; and α (3):−11.69, −25.77, and −34.93 MHz. Detailed SCF MO calculations at the INDO level have been performed to show that the 3αH radical has the general structure of H1Ċ (H2) –CX=C(H3)Y. The relationship of the 3αH radical observed in 5′dCMP, to similar radicals observed in cytidine and 3′CMP, is discussed. A reaction scheme is proposed to show how the 3αH radical could be formed in the C5'–C3' region of the ribose moiety.