Gas phase structure and fragmentation of [Cytosine-Guanine]Ag+ complex studied by mass-resolved IRMPD spectroscopy

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.

Automated summary

The silver-mediated cytosine-guanine [CGAg](+) pair was characterized by mass-resolved IRMPD spectroscopy and electronic structure calculations at the DFT level. Two isomers of the [CGAg](+) complex were identified based on the mass-resolved IRMPD spectra recorded on the mass of each fragment. The yields of each fragment are strongly dependent on the isomer of the precursor ion due to the fragmentation energy of the different channels.