Direct Evidence for Tautomerization of the Uracil Moiety within the Pb²⁺/Uridine-5′-monophosphate Complex: A Combined Tandem Mass Spectrometry and IRMPD study

Jean-Yves Salpin (1) , Sébastien Guillaumont (1) , Daniel Ortiz (1) , Jeanine Tortajada (1) , Philippe Maître (2)

1 LAMBE - Laboratoire Analyse et Modélisation pour la Biologie et l'Environnement
2 LCPO - Laboratoire de Chimie Physique D'Orsay

The structure of the [Pb(UMP)-H]+ (UMP = uridine-5′-monophosphate) complex was studied in the gas phase by combining electrospray ionization (ESI), tandem mass spectrometry, and mid-infrared multiple photon dissociation (IRMPD) spectroscopy. The results obtained show that Pb2+ ions interact not only with the deprotonated phosphate group but also with a carbonyl group of the nucleobase moiety by folding of the mononucleotide, resulting in macrochelates that are not likely to be present in solution. Comparison between the IRMPD and DFT-computed spectra suggests that the ESI-generated complex likely corresponds to a mixture of several structures, and establishes the enolic tautomers as the most abundant species for the [Pb(UMP)-H]+ ion, while the very weak IRMPD signal observed at ∼1763 cm–1 points to a minor population of oxo forms. Our data also suggest that losing the nucleobase residue under CID conditions does not necessarily mean a lack of interaction between the metal and the nucleobase moiety, as commonly reported in the literature for large oligonucleotides.

Mots clés: Carbonyls; Phosphates; Nucleobases; Metals; Ions

Domaines: Chimie-Physique [physics.chem-ph]

Jean-Yves Salpin, Sébastien Guillaumont, Daniel Ortiz, Jeanine Tortajada, Philippe Maître. Direct Evidence for Tautomerization of the Uracil Moiety within the Pb²⁺/Uridine-5′-monophosphate Complex: A Combined Tandem Mass Spectrometry and IRMPD study. Inorganic Chemistry, 2011, 50 (16), pp.7769-7778. ⟨10.1021/ic200918q⟩. ⟨hal-00619190⟩