OH Radical‐Induced Oxidation in Nucleosides and Nucleotides Unraveled by Tandem Mass Spectrometry and Infrared Multiple Photon Dissociation Spectroscopy

OH⋅‐induced oxidation products of DNA nucleosides and nucleotides have been structurally characterized by collision‐induced dissociation tandem mass spectrometry (CID‐MS2) and Infrared Multiple Photon Dissociation (IRMPD) spectroscopy. CID‐MS2 results have shown that the addition of one oxygen atom occurs on the nucleobase moiety. The gas‐phase geometries of +16 mass increment products of 2’‐deoxyadenosine (dA(O)H+), 2’‐deoxyadenosine 5’‐monophosphate (dAMP(O)H+), 2’‐deoxycytidine (dC(O)H+), and 2’‐deoxycytidine 5’‐monophosphate (dCMP(O)H+) are extensively investigated by IRMPD spectroscopy and quantum‐chemical calculations. We show that a carbonyl group is formed at the C8 position after oxidation of 2’‐deoxyadenosine and its monophosphate derivative. For 2’‐deoxycytidine and its monophosphate derivative, the oxygen atom is added to the C5 position to form a C−OH group. IRMPD spectroscopy has been employed for the first time to provide direct structural information on oxidative lesions in DNA model systems. Oxidative lesions in DNA model systems, induced by OH⋅, have been structurally characterized by infrared multiple photon dissociation spectroscopy and density functional theory calculations. The addition of one oxygen atom occurs on the nucleobase moiety.