Abstract
To understand the molecular mechanism of base damages by Auger effect on oxygen and nitrogen atom in DNA molecule, guanine radicals have been studied using a newly developed an EPR spectrometer installed in a soft X-ray beamline in SPring-8. This system enables us to irradiate monochromatic ultrasoft X-rays to a sample and observe radicals induced simultaneously. The unique character of this apparatus revealed the induction of unstable short-lived radicals in guanine pellet sample irradiated in a vacuum at 77 K. The EPR spectrum was clearly distinguished from that of stable one which still exists after exposing to ultrasoft X-rays. Thus, we conclude that 1) short-lived species are mainly induced by as a result of the final state of the resonant Auger process on solely existing oxygen atom in carbonyl group in guanine, 2) Auger events at the other atoms in guanine, namely carbon and nitrogen, do not induce this radical process significantly, even though the abundant of these atoms is dominant in guanine molecule. [J Radiat Res 44:421-422 (2003)]
