Excited-state hydrogen atom abstraction initiates the photochemistry of β-2′-deoxycytidine† †Electronic supplementary information (ESI) available: Including relevant preliminary results as well as illustrations and geometrical parameters of selected structures. See DOI: 10.1039/c4sc03761h Click here for additional data file.

Understanding the effects of ultraviolet radiation on nucleotides in solution is an important step towards a comprehensive description of the photochemistry of nucleic acids and their constituents. Apart from having implications for mutagenesis and DNA photoprotection mechanisms, the photochemistry of cytidines is a central element in UV-assisted syntheses of pyrimidine nucleotides under prebiotically plausible conditions. In this contribution, we present UV-irradiation experiments of β-2'-deoxycytidine in aqueous solution involving H-D exchange followed by NMR spectroscopic analysis of the photoproducts. We further elucidate the outcome of these experiments by means of high-level quantum chemical calculations. In particular, we show that prolonged UV-irradiation of cytidine may lead to H-C1' hydrogen atom abstraction by the carbonyl oxygen atom of cytosine. This process may enable photoanomerisation and nucleobase loss, two previously unexplained photoreactions observed in pyrimidine nucleotides.