Photodamage to isolated mononucleotides--photodissociation spectra and fragment channels.

UV excitation of isolated singly-charged deprotonated mononucleotide anions in the gas phase can lead to their dissociation. We present mass spectrometry results, photodepletion and photofragment action spectra on the UV-photodissociation of deprotonated 2'-deoxyribonucleobase-5'-monophosphates with adenine, cytosine, guanine and thymine as nucleobases. We observe the same anionic fragments as in earlier experiments on collision-induced dissociation, although their relative intensities are quite different, especially with respect to the abundance of the deprotonated base anions. The fragment channels correspond to loss of genetic information by cleavage of the CN glycosidic bond and to strand breaking by severing the phosphate-sugar link. We compare the photodissociation spectra with UV absorption spectra of aqueous solutions of the same species and discuss the photodissociation behavior in the context of possible mechanisms and ergodic versus non-ergodic fragmentation.