Infrared Characterization of the Guanine Radical Cation: Finger Printing DNA Damage

Oxidation of DNA represents a major pathway of genetic mutation. We have applied infrared spectroscopy in 77 K glass with supporting density functional theory (DFT) calculations (EDFI/6-31+G*) to provide an IR signature Of the guanine radical cation G(+center dot), formed as a result of 193 nm photoionization of DNA. Deprotonation of this species to produce the neutral radical G(-H)(center dot) does not occur in 77 K glass. DFT calculations indicate that the formation of G(+center dot) within the double helix does not significantly Perturb the geometry of the G/C pair, even though there is a significant movement of the N-1 proton away from G toward C. However, this is in stark contrast to drastic changes that are expected if Full deprotonation of G/C Occurs, producing the G(-H)(center dot)/C pair. These results are discussed in light Of solution-phase time-resolved IR spectroscopic studies and demonstrate the power of IR to follow dynamics of DNA damage ill natural environments.