One-electron oxidation of 2'-deoxyadenosine-5'-phosphate: comparisons of theoretical calculations with experimental values.

A recent paper by Hou et al. (Hou, R.; Gu, J.; Xie, Y.; Yi, X.; Schaefer, H. F. J. Phys. Chem. B 2005, 109, 22053) on 2'-deoxyadenosine-5'-phosphate (5'-dAMP) reports calculations on one-electron oxidation of the 5'-dAMP anion. The paper presents a very interesting observation that, for the radical produced by electron removal, the unpaired spin density resides on both the phosphate and the adenine base moieties. There are also indications that this radical has a weakened C5'-O5' bond, and it is said that this may be the origin of a single-strand break in DNA. New calculations have been performed to show that the spin density on the phosphate is dependent on the charge on the phosphate. The use of the B3LYP method with the 6-31G(d) basis set yields results very similar to those obtained with the much larger B3LYP/DZP++ basis set in computing the structures of one electron oxidized 5'-dAMP. New calculations on the isotropic hyperfine couplings in 5'-dAMP are presented to show under just what conditions one might expect to see small amounts of unpaired spin density on the phosphates. Results show that this may occur in gas-phase studies of nucleotides but, most likely, not in DNA.