Investigation of the Reactivity of the Cytosine-5-yl Radical Ion using Ion Trap Mass Spectrometry

Nucleobases play a significant biological role in DNA and RNA. Since the discovery that halogenated pyrimidines act as a good sensitizer for radiotherapy, the attention on 5-halouracil has increased, however the photoreactivity of cytosine and its derivatives has not been investigated. This study presents, for the first time, the highly selective generation of the cytosine-5-yl radical ion obtained by photodissociation of halogenated precursors. Using a modified linear ion trap mass spectrometer, gas-phase reactions and product channels are presented and mechanisms of possible pathways of photodissociation are discussed for reactions between the radical ion with molecular oxygen and unsaturated hydrocarbons including, propene, propyne and acetylene. Molecular oxygen reacting with the protonated cytosine-5-yl radical forms products at m/z 126 and 127, showing an efficiency of 𝜙 = 11.4 ± 0.9%. Reactions of propene and propyne present an efficiency of 𝜙 = 52.6 ± 0.8% and 𝜙 = 111 ± 0.1%, showing that unsaturated hydrocarbons reactions are highly efficient and significantly more efficient than molecular oxygen reactions.