Gas‐Phase Interactions between Lead(II) Ions and Cytosine: Tandem Mass Spectrometry and Infrared Multiple‐Photon Dissociation Spectroscopy Study

Abstract

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.

Structure of protonated thymidine characterized by infrared multiple photon dissociation and quantum calculations

“…During the last decade, InfraRed Multiple Photon Dissociation (IRMPD) spectroscopy has been established as a powerful approach for probing the structure of gaseous ions . In this context, this technique has been notably widely applied to study the structure of either bare or metal‐cationized DNA building blocks . Many studies were motivated by the probable relationship between the presence of rare enol tautomers of nucleobases within nucleic acid building blocks and point mutation developing during nucleic acid replication .…”

“…[1][2][3][4][5] In this context, this technique has been notably widely applied to study the structure of either bare [6][7][8][9][10][11][12][13][14][15][16][17][18][19] or metal-cationized DNA building blocks. [20][21][22][23][24][25][26][27][28][29][30][31][32][33] Many studies were motivated by the probable relationship between the presence of rare enol tautomers of nucleobases within nucleic acid building blocks and point mutation developing during nucleic acid replication. [34][35][36][37][38][39] The evaluation of the tautomeric behaviour of nucleobases is therefore of fundamental importance.…”

Interactions of Dimethyltin(IV) with Uracil As Studied in the Gas Phase

“…Protonated uracil (m/z 113) is observed in significant abundance but does not dominate the spectrum, as it has been observed for instance for the Pb 2+ /cytosine system. 21 This is not unexpected because uracil is much less basic than cytosine in the gas phase. 22 Tin-containing ions can be easily identified because of the specific isotopic distribution of this metal, resulting in characteristic isotopic profiles.…”

Protonation of methyluracils in the gas phase: The particular case of 3-methyluracil

“…Among those, Infrared Multiple Photon Dissociation spectroscopy (IRMPD) of mass-selected ions, is now established as a very powerful approach to probe the structure of gaseous ions of moderate size, [7][8][9][10], and different groups have used IRMPD spectroscopy to study the structure and tautomerization of protonated DNA and RNA building blocks generated by electrospray [11][12][13][14][15][16][17][18][19][20][21][22][23][24]. In our continuing effort to study the structure and unimolecular reactivity of gaseous nucleobases, either protonated [11][12][13]25,26] or complexed to metals [27][28][29][30][31][32], the present paper reports the IRMPD study in the fingerprint region between 1000 and 2000 cm -1 of three protonated methyluracils, namely 1-Me, 3-Me and 6-Me-uracil (Scheme 1), generated by electrospray ionization and trapped in a quadrupole ion trap. The study is complemented by DFT and ab-initio electronic structure calculations that provide information regarding the relative stability of the different conformers and their vibrational modes.…”