UV-photodissociation of non-cyclic and cyclic mononucleotides

Irradiation of nucleotides in the gas phase with ultraviolet light can lead to their fragmentation. We present a comparison of UV photofragmentation data on ribo-, deoxyribo- and cyclic nucleotides with guanine and adenine as nucleobases. The envelope of the UV photofragment spectra does not depend significantly on the detailed structure of the sugar–phosphate backbone. The fragment channels observed in the photofragmentation of ribonucleotides are very similar to those of deoxyribonucleotides with small differences in the relative abundances of the product ions. In fragmentation of cyclic nucleotides, the deprotonated base anions are the most abundant fragments, in contrast to the non-cyclic nucleotides, where this channel is significantly weaker. We discuss the abundances in the context of possible fragmentation mechanisms and structural differences of the parent molecules.

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► Photodissociation of cyclic mononucleotides after UV excitation occurs predominantly by loss of anionic base.
► Decay of RNA and DNA mononucleotides is dominated by loss of neutral base and loss of phosphate-based anions.
► Differences between cyclic and non-cyclic fragmentation pathways can be attributed to different tethering of the phosphate group.
► The presence of different functional groups on the phosphate–sugar “backbone” of cyclic and non-cyclic nucleotides does not affect the envelope of the electronic spectra of adenosine and guanosine-based nucleotides.