Gas-phase interactions between lead(II) ions and cytosine: tandem mass spectrometry and infrared multiple-photon...

Gas-phase interactions between Pb(2+) ions and cytosine (C) were studied by combining tandem mass spectrometry, infrared multiple photon dissociation spectroscopy, and density functional theory (DFT) calculations. Both singly and doubly charged complexes were generated by electrospray. The [Pb(C)-H](+) complex was extensively studied, and this study shows that two structures, involving the interaction of the metal with the deprotonated canonical keto-amino tautomer of cytosine, are generated in the gas phase; the prominent structure is the bidentate form involving both the N1 and O2 electronegative centers. The DFT study also points out a significant charge transfer from the nucleobase to the low-lying p orbitals of the metal and a strong polarization of the base upon complexation. The various potential energy surfaces explored to account for the fragmentation observed are consistent with the high abundance of the [PbNH2](+) fragment ion.