Decomposition of purine nucleobases by very low energy electrons

Abstract

We show that low energy electrons effectively decompose the gas phase purine nucleobases adenine (A) and guanine (G) via dissociative electron attachment (DEA) involving low lying (<3 eV) shape resonances, but also via core excited resonances (located near 6 eV). In adenine the low energy resonances exclusively lead to dehydrogenation, i.e. ejection of a neutral hydrogen radical with the excess electron remaining on the molecule. This reaction by far dominates DEA in the entire energy range 0–15 eV, similar to the situation recently observed in the pyrimidine bases thymine (T), cytosine (C) and uracil (U). In striking contrast to that, guanine behaves very different in that dehydrogenation is comparatively weak while various further decomposition reactions are observed from the low energy π* precursor ions. These reactions lead to fragment ions of the form (G–O/NH2)-, O-/NH2-, (G–HOCN)-, OCN-, CN- indicative of single bond cleavages but also more complex unimolecular decompositions associated with the excision of cyano units from the cyclic structure. Since electrons are the predominant secondary species in the interaction of high energy quanta with biological material, electron driven reactions represent initial steps in the molecular description of radiation damage.