Gas-Phase Conformations and N-Glycosidic Bond Stabilities of Sodium Cationized 2′-Deoxyguanosine and Guanosine: Sodium Cations Preferentially Bind to the Guanine Residue

2'-Deoxyguanodne (dGuo) and guanosine (Quo) are fundamental building blocks of DNA and RNA nucleic acids. In order to understand the effects of sodium cationization on the gas-phase conformations and stabilities of dGuo and Guo, infrared multiple photon dissociation (IRMPD) action spectroscopy experiments and complementary electronic structure calculations are performed. The measured IRMPD spectra of [dGuoi-Na](+) and [Guo+Na](+) are compared to calculated IR spectra predicted for the stable low-energy structures computed for these species to determine the most favorable sodium cation binding sites, identify the structures populated in the experiments, and elucidate the influence of the 2'-hydroxyl substituent on the structures and IRMPD spectral features. These results are compared with those from a previous IRMPD study of the protonated guanine nucleosides to elucidate the differences between sodium cationization and protonation on structure. Energy-resolved collision-induced dissociation (ER-CID) experiments and survival yield analyses of protonated and sodium cationized dGuo and Guo are performed to compare the effects of these cations toward activating the N-glycosidic bonds of these nucleosides. For both [dGuo+Na](+) and [Guo-FiNa](+) the gas-phase structures populated in the experiments are found to involve bidentate binding of the sodium cation to the O6 and N7 atoms of guanine, forming a 5-membered chelation ring, with guanine found in both anti and syn orientations and C2'-endo (T-2(3) or T-3(2)) puckering of the sugar. The ER-CID results, IRMPD yields and the computed Cl' N9 bond lengths indicate that sodium cationization activates the N-glycosidic bond less effectively than protonation for both dGuo and Guo. The 2'-hydroxyl substituent of Guo is found to impact the preferred structures very little except that it enables a 2'OH-3'OH hydrogen bond to be formed; and stabilizes the N-glycosidic bond relative to that of dGuo in both the sodium eaticinized and protonated complexes.