THEORETICAL-STUDY ON THE DEOXYRIBOSE RADICALS FORMED BY HYDROGEN ABSTRACTION

The structures of C1, C2, C3, and C4 centered deoxyribose radicals are optimized at the UHF/6-31G level. For each radical two puckered confo rmations are observed, which are significantly different from those of deoxyribose. In C1 and C2 radicals the pseudorotation angle, P, is sh ifted toward higher values compared to that of deoxyribose. In C3 and C4 radicals the shift of P is in the opposite direction. In addition, the puckering amplitude tau(m) is significantly decreased in the radic als, indicating a flattening of the five-membered ring. The C2 centere d radical has the sp2-type electronic structure, while C1, C3, and C4 centered radicals are pyramidal. The enthalpies for H-atom abstraction from deoxyribose are calculated at the MP2/6-31G level including ZPE and a scaling of correlation energy. The abstractions from C1, C3, an d C4 positions require similar energies, whereas the abstraction from the C2 carbon of deoxyribose is less favorable by 3-4 kcal/mol. The su sceptibility of different deoxyribose hydrogens for abstraction is est imated on the basis of their bond strength and their accessibility in nucleotides and in DNA.