Production and Structure Study of Free Radicals of Bases and Nucleosides in Gas Phase

Nucleoside free radicals have important functions in organisms and play a crucial role in DNA damage. Accurately understanding the structure of nucleoside free radicals is crucial for studying their properties, reaction mechanisms, and interactions with other biomolecules. The high vacuum in the mass spectrometer provides an inert environment for free radicals. Further tandem mass spectrometry combined with theoretical calculation is crucial for achieving their structural informations. This article reviewed gas phase studies of base and nucleoside radicals based on mass spectrometry in the past two decades, and provided a detailed introduction and comparison of their production methods, structural research methods and progress. Different methods were developed for the generation of the free radical ions, including collision induced dissociation of precursor ions of ternary transition metal complexes or those introducing free radical initiators, electron transfer dissociation of precursor ions charge-tagged, and UV photodissociation of precursor ions including C-I bonds. Besides, the methods for studying the structure of free radical ions in gas phase have gradually enriched, including commonly used tandem mass spectrometry, UV-visible and IR photodissociation spectroscopy. Based on the above methods, many different base and nucleoside free radical ions were generated and structurally determined in gas phase. On the other hand, the research of the highly active free radical intermediates and the selective generation of free radical isomers still pose challenges, and there is an urgent need to develop new experimental method.