Gas phase structure and fragmentation of [Cytosine-Guanine]$$\hbox {Ag}^{+}$$ complex studied by mass-resolved IRMPD spectroscopy

Abstract

The silver-mediated cytosine-guanine [CGAg] $$^{+}$$ pair was characterized by mass-resolved IRMPD spectroscopy and electronic structure calculations at the DFT level. Three fragments were observed: [GAg] $$^{+}$$ , [CAg] $$^{+}$$ and [CH] $$^{+}$$ . From the mass-resolved IRMPD spectra recorded on the mass of each fragment, two isomers of the [CGAg] $$^{+}$$ complex were identified. The most populated isomer is a Hoogsteen structure [HooAg] $$^{+}$$ between canonical cytosine (CKA(1)) and canonical guanine (GKA(9)), while the second isomer is an altered-Hoogsteen-like pair [*HooAg] $$^{+}$$ in which guanine is in a non-canonical form (GKA(7)). The determined yields of each fragment are strongly dependent of the isomer of the precursor ion because of the fragmentation energy of the different channels. Finally, the [CH] $$^{+}$$ is suggested to be produced by a metal-assisted proton transfer from guanine to cytosine preceded by an isomerization of the [HooAg] $$^{+}$$ isomer.