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Gas-Phase reactivity of Pb2+ ions towards adenine, thymine and uracil
Jean-Yves Salpin, Sébastien Guillaumont, Jeanine Tortajada
To cite this version:
Jean-Yves Salpin, Sébastien Guillaumont, Jeanine Tortajada. Gas-Phase reactivity of Pb2+ ions towards adenine, thymine and uracil. Modelling chemical reactivity: from gas-phase to solution and enzymes. An international conference in honor of Professor Jean-Louis Rivail, 2003, Nancy, France. 2003. �hal-00069111�
Methodology
Introduction
Gas-phase reactivity of Pb
2+
ions with adenine, thymine and uracil
Laboratoire Analyse et Environnement
Results
Bâtiment des Sciences - Université d’Evry Val d’Essonne - Boulevard François Mitterrrand - 91025 Evry Cedex - France
• Geometry optimization and vibrational analysis at B3LYP/6-31G(d,p) and G96LYP /6-31G(d,p) levels.
• NBO analysis.
• Many studies have shown that in physiological media, Pb(II) ions are determinant in the activity of some RNA-cleaving ribozymes . Moreover, it recently appeared that some ribozymes require the presence of two metal cations.(1,2) It was thus observed that in solution, Pb2+ cations do not exhibit any
particular reactivity with the DNA, whereas they induce the cleavage of the RNA in the presence of Mg2+. On the other hand, few is known about the
intimate mechanisms associated with these interactions. In this context, we began a study in order to have a better understanding of these mechanisms, by considering in a first step the gas-phase reactivity between Pb2+ ions and three nucleobases: thymine (T, R=CH
3), uracil (U R=H), and
adenine (A).
•
Electrospray/Triple quadrupole tandem mass spectrometer.•
Pb(NO3)2/nucleobase solutions (5.10-5 mol.L-1/10-4 mol.L-1) in water or in awather/methanol (50/50) mixture.
Mass Spectrometry•
Flow rate: 5l/min•
Temperature : 373 KJean-Yves Salpin, Sébastien Guillaumont, Jeanine Tortajada
DFT calculations• Use of the Stuttgart quasi-relativistic pseudo-potential to describe the lead atom.
HN N H O O R 4 6 1 2 3 5 N N N N H NH2 1 2 3 5 4 6 7 8 9 10
•
MS/MS experiments : collision gas N2 (P 2 10-5 Torr )• Formation of [Pb(B)n – H]+ ions (n=1-3), the most intense ion corresponding to the complexation of a single nucleobase.
• Characterization of ions [Pb(B) - H]+ : MS/MS experiments and theoretical calculations.
• Results obtained for thymine and uracile are totally comparable.
Pyrimidic bases : thymine and uracil• MS/MS spectrum of the ion [Pb(T)-H]+ (m/z 333)
100 150 200 250 300 m/z, amu 0% 20% 40% 60% 80% 100% Re l. In t. ( % ) 250 333 263 208 290 225 82 thymine HN N H O O CH3 100 150 200 250 300 m/z, amu 0% 20% 40% 60% 80% 100% Re l. In t. ( % ) 251 334 263 208 290 225 82 2-13C-thymine HN N H O O CH3 * m/z 225 [PbOH]+ [Pb(T)-H]+ [Pb(NCO)]+ -NCO. - Pb m/z 333 m/z 290 m/z 263 m/z 82 m/z 250 m/z 208 m/z 209 PbH+ (m/z 225) (m/z 334) (m/z 290) (m/z 263) (m/z 82) (m/z 251) Pb+ (m/z 208) (m/z 209) -C5H4N2O -HNCO -C4H5NO -HCN -C4H3NO
The elimination of HNCO specifically induces
the carbon C(2).
The ion [PbNCO]+ specifically induces the
carbon N°2.
Puric base : adenine• DFT calculations : preferential deprotonation of the least acidic site (N3)
• Mechanisms of dissociation
0 +14.6
+16.9 +25.1+24.4 +28.8+30.5
• MS/MS spectrum of the ion [Pb(A)-H]+ (m/z 342)
100 150 200 250 300 350 m/z, amu 0% 20% 40% 60% 80% 100% Re l. In t. ( % ) 342 208 315 134 288
The fragmentations leading to the reduction of lead are particularly favorable (m/z 134 and
208). N N N N H H2N N N N N H H2N * 100 150 200 250 300 350 m/z, amu 0% 20% 40% 60% 80% 100% Re l. In t. ( % ) 343 208 315 135 288 316 [C5H4N5]+ m/z 342 (m/z 343) m/z 288 m/z 134 (m/z 135) m/z 208 [Pb(A)-H]+ m/z 315-316 Pb+ - HCN (85%)
*
- HCN (15%)*
-Pb -C5H4N5• DFT calculations : preferential deprotonation of the least acidic site (N10)
• Mechanisms of dissociation adenine 2-13C-adénine N N N N N H H H H Pb N C N N N N H H H H Pb N N N N H H H Pb N C H + m/z 342 * * m/z 315 N N N N N H H H H * - Pb m/z 134 *
(1) T. Pan, O. C. Uhlenbeck,
Nature
358, 560 (1992).(2) M. H. Kim, M. Katahira, T. Sugiyama, S. Uesugi
J. Biochem.
122,1062 (1997).
References
0 +12.1
+12.8 +24.9+25.5 +69.5+66.7
• Relative energies refined with an extended 6-311+G(3df,2p) like basis set (given in kJ.mol-1 ).
[Pb(T)-H]+ ions correspond to a mixture of
several structures. N3 C2 N1 H C6 C5 C O O CH3 H Pb N3 C2 N1 H C6 C5 C4 O O CH3 H Pb N3 C2 Pb O + m/z 333 m/z 250 + + + N1 C6 C5 C4 O CH3 H H N3 C2 N1 C6 C5 C4 O O CH3 H H Pb + N3 C2 N1 C6 C5 C4 O O CH3 H H Pb + + m/z 333 m/z 290
